RECALLS page 16-34 Flashcards
(348 cards)
1
Q
A blood sample is 7 days old and stored at 4°C. Which test can you perform?
A
Hemoglobin (Hgb)
2
Q
If you see granules but no blasts on the smear, what should you do?
A
Consider it normal; verify the results.
3
Q
What is an advantage of the buffy coat smear over a wedge-shaped smear?
A
Abnormal nucleated cells are more easily found; easier differentiation of WBCs.
4
Q
If there is an nRBC flag, which parameters can still be reported?
A
Platelets and RBCs (or platelets and WBCs depending on context/flag resolution).
5
Q
Which condition is an acquired hemolytic anemia?
A
Fanconi anemia.
6
Q
CBC results change significantly after 4 hours. What is the next step?
A
Repeat the test.
7
Q
Hemoglobin result was 140 g/L and becomes 180 g/L. What is the likely cause?
A
Dehydration.
8
Q
In megaloblastic anemia, how does the scatter plot shift?
A
RBC to the right, platelets to the left; WBC scatter remains normal.
9
Q
What are typical findings in polycythemia vera?
A
High platelet count, high LAP score, low WBC count.
10
Q
In hereditary spherocytosis, which parameter is changed?
A
MCHC (increased).
11
Q
What does it mean if PT/APTT is prolonged but corrects after mixing studies?
A
Factor deficiency.
12
Q
What does it mean if PT/APTT is prolonged and does not correct after mixing studies?
A
Presence of a non-specific inhibitor (e.g., lupus anticoagulant, excessive anticoagulant use).
13
Q
What is the use of ISI (International Sensitivity Index), and what is done when a new PT reagent lot has a different ISI?
A
ISI standardizes PT to calculate INR; update the ISI value in the system when reagent lot changes.
14
Q
What is the most common problem encountered in fluorometry?
A
Quenching.
15
Q
Which hematology parameters are affected in a lipemic sample?
A
MCH, MCHC, and Hemoglobin (Hgb).
16
Q
What parameters increase falsely when a cold antibody sample is kept refrigerated and tested the next day?
A
False-positive results; usually affects MCV and WBC.
17
Q
When should fractionated vs. unfractionated heparin be used?
A
• Unfractionated heparin: monitored by aPTT
• Fractionated (low-molecular-weight) heparin: monitored by Factor Xa assay.
18
Q
What is used to monitor Factor X activity and aPTT in patients on heparin therapy?
A
Factor X assay for low-molecular-weight heparin; aPTT for unfractionated heparin.
19
Q
Which anemia matches the following results: RBC = 3.30 x10¹²/L, Hgb = 110 g/L, Hct = 0.298 L/L?
A
Aplastic anemia.
20
Q
Which lab result must be immediately reported to a physician?
A
Hemoglobin = 55 g/L.
21
Q
Where should Glacial Acetic Acid be stored?
A
Close to the floor / close to gravity.
22
Q
What is the color of Pneumocystis carinii in a GMS stain?
A
Black.
23
Q
Which stain is used for P. carinii?
A
Silver stain.
24
Q
What should be done if fungus is overstained with silver?
A
Recut and stain again.
25
In dehydration, what can be used as a replacement?
Isopropyl alcohol.
26
What is the result of hematoxylin being too acidic?
The stain appears red.
27
Which part of the cell is stained by the acidic dye in H&E staining?
Cytoplasm.
28
Which part of the cell is stained by the basic dye in H&E staining?
Nuclei.
29
What is the action of an acid decalcifying fluid?
Removes calcium (Ca++).
30
What is the decolorizer used in H&E staining?
Acid alcohol.
31
What is the function of alum in H&E staining?
It acts as a mordant.
32
What causes amorphous yellow dusts in H&E stained slides?
Bile pigments.
33
What causes a pink artifact (eosinophilic background staining) in H&E staining?
Adhesive contamination.
34
What should be done if blue color does not appear in H&E stain?
Return the slide to the blueing agent.
35
On an H&E stained slide, eosin appears pale. What is the likely cause?
Blueing agent was not rinsed well.
36
What molecule has both positive and negative charges?
Ampholytes.
37
What is the black pigment in the mediastinal node on an H&E stained slide?
Carbon.
38
What special stain is used for amyloid bodies?
Congo Red.
39
What is the most specific method for detecting amyloid?
Green birefringence with polarized light.
40
What is required for tissue sectioning when staining for amyloid?
Thicker sections.
41
What does a Trichrome stain help identify?
Fibrosis.
42
Which stain is used for demonstrating high collagen content in liver tissue?
Masson’s Trichrome.
43
What does green cytoplasm in MTS indicate?
Incomplete time in phosphomolybdic acid (PMA).
44
What is used to destain Giemsa stain?
Methanol.
45
How do you destain H&E stained tissue?
Acid alcohol.
46
What is the chelating agent commonly used for decalcification?
EDTA.
47
Which fixative cannot be used in lysochrome (fat stain) procedures?
Alcohol-based fixatives.
48
During which step of tissue processing does glycogen streaming occur?
Fixation.
49
Which specimen requires critical orientation during embedding?
Colon.
50
Non-specific aldehyde staining on a slide is most likely due to what issue?
Improper fixation (e.g., glutaraldehyde use).
51
What fixative artifact has an affinity with heme pigments?
Formalin (can be treated with picric acid).
52
What is the purpose of post-fixation with picric acid?
Acts as a mordant for subsequent staining.
53
In reticulin staining, what removes unreduced silver?
Sodium thiosulfate.
54
What is the reducer used in the Gordon and Sweets reticulin stain?
10% formalin.
55
How can silver oxidation be prevented in reticulin staining?
Use of sodium thiosulfate.
56
What is the reducer in the Von Kossa staining method?
Sunlight or UV light.
57
Why might a Von Kossa control test be negative?
Insufficient exposure to light.
58
Why is the target tissue unstained in a Von Kossa stain?
Underexposure to sunlight.
59
Which fixative is contraindicated for AFB (Acid-Fast Bacilli) staining?
Carnoy’s fluid.
60
What causes section detachment during reticulin staining?
Alkalinity of the solution.
61
What does it mean if there is no band in both the control and test in an immunochromatography test?
The test is invalid.
62
In immunocytochemistry, which step is used to remove background staining?
Heat.
63
Pale eosin staining is due to what?
High pH.
64
Two-week fixation is typically required for which tissue?
Brain.
65
How should silver solutions be disposed of?
Neutralize with chloride (e.g., 0.85% NaCl or 1.0% HCl), then dispose down the drain with lots of water.
66
If the cryostat wheel is stuck, what is the likely issue?
Frozen mechanism due to improper disinfectant (e.g., water instead of glutaraldehyde).
67
What tissue must be opened, washed, and pinned during preparation?
Large intestine.
68
Which biopsy requires critical orientation?
Duodenal biopsy.
69
What causes microchatter or chattering artifacts in sectioning?
Overdehydration or block too cold.
70
What causes ice crystal artifacts in frozen sections?
Slow freezing.
71
What causes cryostat ribbons to crumble?
Block too cold or presence of ice crystals; should use flash freezing.
72
What causes a milky appearance on slides?
Improper dehydration.
73
What happens if sections are cut too fast during trimming?
Sections will curl.
74
What causes a soft uterus block with white powder residue?
Insufficient dehydration using unordered alcohol concentrations.
75
What is the result of misalignment of the anti-roll device in cryostat sectioning?
Tissue will not fall properly.
76
What does shiny and moist tissue during sectioning indicate?
Improper fixation.
77
What causes soft and wet tissue blocks?
Incomplete dehydration or incomplete processing.
78
What causes a brownish color of nuclei on an H&E slide?
Change or oxidation of hematoxylin.
79
If H&E slides still show red-brown nuclei after hematoxylin is changed, what should be adjusted?
Increase the pH of the lithium carbonate bluing step.
80
What causes patchy staining in H&E slides?
Improper fixation.
81
What causes non-stained patches in an H&E section?
Incomplete removal of paraffin.
82
What causes thick and thin sections during microtomy?
Loose knife/screw or tilt of the knife.
83
While cutting a block you notice a line on the section. What could be the reason?
Calcium deposits.
84
What substance is added to paraffin to improve sectioning quality?
Plasticizer.
85
New paraffin typically contains what additive?
Resins.
86
What is the use of picric acid in histology?
Enhances staining.
87
What processing error causes precipitate on sections?
Placing tissue directly in 95% ROH or using unfiltered hematoxylin.
88
PAS and PAS-D stains are used to demonstrate what substance?
Glycogen.
89
At what temperature should Schiff reagent be stored?
4°C.
90
Schiff reagent did not produce enough aldehyde groups and lost sensitivity. What should be done?
Replace the Schiff reagent.
91
How is mercury pigment removed from tissues?
Alcohol, iodine, and sodium thiosulfate.
92
How is formalin pigment removed from tissues?
Picric acid.
93
What is the reducer used in Verhoeff-Van Gieson (VVG) staining?
Ferric chloride (FeCl₃).
94
How should picric acid be properly stored?
In an amber bottle and kept under water.
95
What test identifies dark brown pigments in H&E stained slides?
Perl’s Prussian Blue stain.
96
Homogeneous material seen in H&E sections is identified by which stain?
Congo Red.
97
If tissue falls off the slide during Congo Red staining, what is the likely cause?
Alkalinity of the solution.
98
In a series of six serial sections, tissue appears on slide 6 but not on slides 1–5. What is the most likely reason?
Floater on the water bath.
99
How do you enhance the visualization of the basement membrane in a 2-micron section?
Prolong the staining.
100
What is important when using automatic tissue processors?
Always flush the lines.
101
What type of chemical reaction is not seen in histopathology?
Covalent bonding.
102
In microtomy, why is coarse trimming performed?
To expose the tissue.
103
When cutting a tissue, you notice a white line on one side of the section. What is the likely cause?
Calcium deposits.
104
What is the recommended temperature for the water bath in the histology lab?
10°C below the melting point (MP) of paraffin.
105
While reviewing an H&E-stained slide, you notice pink, homogeneous sections in the tissue. What stain is best to identify the material?
Congo Red.
106
How can ice crystals be prevented from forming in tissue when using a cryostat?
Cover the tissue with saline and flash freeze.
107
In a Verhoeff-Van Gieson (VVG) stain, how does the tissue appear before differentiation?
Yellow.
108
What is a good control for a Gram stain?
Appendix with Enterococcus faecalis and normal flora.
109
What stain is used to demonstrate neutral mucin?
Periodic Acid-Schiff (PAS).
110
In H&E staining, what color do nuclei appear after applying lithium carbonate (a bluing reagent)?
Blue.
111
In Congo Red staining, the amyloid control is positive, but the kidney section is negative. What is the most likely cause?
The kidney section is too thin.
112
Granulomas seen in H&E-stained slides may be further investigated with which stains?
Grocott Methenamine Silver (GMS), Ziehl-Neelsen (ZN), or Giemsa (GM).
113
You observe that both nuclei and background are blue in an H&E stain. What can you do to prevent this?
Decrease the time in hematoxylin.
114
Why is increasing concentration of alcohol used during dehydration in histology?
To avoid shrinkage and distortion of tissue.
115
Which of the following actions is part of preventive maintenance for a microtome?
Lubricating the instrument.
116
How can ice crystal formation be prevented when using a cryostat?
Cover with saline and flash freeze.
117
A score line is found in the tissue block even after a new blade is used. What is the likely cause?
Presence of calcium deposits.
118
Black deposits in a mediastinal lymph node indicate the presence of what substance?
Carbon.
119
Why is it necessary to report a leaking container of picric acid?
It is explosive when dry.
120
What is a positive control for Perl’s Prussian Blue (PPB) stain?
Spleen, liver, or bone marrow.
121
What is a positive control for Masson’s Trichrome Stain (MTS)?
Fibrosis.
122
What stain is used to demonstrate colonic mucin?
Alcian blue at pH 2.5.
123
In GMS staining, what causes loss of specificity by staining all substances?
Overstaining.
124
What can cause false-positive staining in the immunoperoxidase method?
Endogenous peroxidase activity.
125
What should you do to reduce nonspecific staining in immunohistochemistry?
Dilute the antibody.
126
In immunohistochemistry, why might RBCs and WBCs appear brown?
Due to unquenched endogenous peroxidase.
127
When preparing a standard for immunoassay, what happens if it is diluted twice as much as intended?
Patient results will appear falsely decreased.
128
What is used to block endogenous biotin in immunohistochemistry?
Avidin-biotin blocking system (Avidin/biotin block).
129
What should you do if tubes break in the centrifuge?
Wait 30 minutes before opening the lid.
130
What should you do in case of a small acid spill on the body?
Rinse with a copious amount of water.
131
What should you do if there is an acid spill on the floor?
Use an acid neutralization kit.
132
Which chemical is corrosive to metals?
Sodium hypochlorite.
133
Oxidizing chemicals must NOT be stored with which type of material?
Flammables.
134
What should you wear to protect against airborne hazards?
N95 mask.
135
What is the first step if someone is experiencing electric shock?
Unplug the electric source or turn off ignition sources.
136
What should be done if an electrical cord is frayed in the lab?
Place an out-of-order sign and call maintenance.
137
What is the best-practice method for disposing of blood?
Commercial disposal method.
138
You see dry picric acid powder on the outside of a bottle on a shelf. What should you do?
Call the hazardous waste disposal team.
139
What type of fire extinguisher is used for electrical equipment fires?
CO₂ extinguisher.
140
What is the safest method of opening a blood tube?
Use a biosafety cabinet.
141
What should be done in the case of a large xylene spill?
Evacuate the lab.
142
What is used to clean microscope objective lenses?
70% alcohol.
143
How long should you flush your eyes if splashed with acid?
15 minutes.
144
What PPE should be used during a nitric acid spill?
Rubber gloves.
145
Which chemical requires storage in a low-gravity fume hood?
Nitric acid or glacial acetic acid.
146
What should be done after a large spill of flammable liquid?
Report to the maintenance department.
147
What is used to disinfect a cryostat?
2% glutaraldehyde.
148
What is used to disinfect a cryo knife used on a pneumonia or TB-positive patient?
Phenol.
149
What is used to disinfect a cryo knife used on a CJD-positive patient?
10% Sodium hydroxide.
150
What are the autoclave time and temperature requirements?
15 minutes at 15 psi and 121°C.
151
Where should an eye wash station be located?
Within 10 seconds walking distance from eye hazards.
152
What should you do if you have a cut on your hand while working in the lab?
Wear gloves.
153
What is the correct order for wearing PPE?
Gown, mask, gloves.
154
What should you do in the event of a flammable acid spill?
Turn off electronic equipment.
155
What must be done with ethanol samples in the lab?
Ensure the sample is capped.
156
What should you do when the sharps bin is ¾ full?
Close the lid and replace it with a new bin.
157
A contagious infection is spreading in the hospital. What is the mode of transmission?
Droplets.
158
The centrifuge motor is on fire. What class of fire extinguisher should be used?
Class C.
159
What is the best antiseptic for blood alcohol testing?
Soap and water.
160
What collection method should be used for a 3-day-old neonate requiring venipuncture?
Heel puncture with an EDTA microtainer.
161
Swelling occurs during blood draw. What is the correct procedure?
Withdraw the needle, apply pressure for 2 minutes, bandage, and instruct the patient to continue applying pressure.
162
Another healthcare professional brings a properly labeled tube for an LDH test. What should you do?
Enter it into the LIS (since LDH is not time-sensitive).
163
How should a sample for Neisseria gonorrhoeae be transported?
Use a cotton swab in Amies transport medium.
164
Which anticoagulant can be used for magnesium (Mg) determination?
Heparin.
165
A Foley catheter needle is received for CSF collection. What should you do?
Reject the specimen.
166
What is the purpose of SPS (Sodium Polyanethol Sulfonate) in blood culture bottles?
It acts as an anticoagulant.
167
What is the effect on glucose results if a whole blood sample is left unprocessed for more than 1 hour?
Glucose decreases by approximately 7%.
168
A patient appears pale, weak, and sweaty. What is the likely cause?
Anxiety.
169
How should you confirm the identity of a sleeping patient before drawing blood?
Check the wristband and wake the patient for verbal confirmation.
170
A stroke patient has blurred speech. How should you proceed?
Use body language to demonstrate what you are going to do.
171
You issued a test report, but a nurse calls saying the test wasn’t requested for that patient. What should you do first?
Check the specimen ID.
172
A CBC result shows low platelets. Manual review reveals platelet satellitism around neutrophils. What should you do?
Request a new sample.
173
In a lipemic sample, which parameter is affected?
Hemoglobin (Hgb), MCHC.
174
Nurse did not note if the patient is on anticoagulants. APTT is elevated. What should you do?
Call the nurse to confirm the type of anticoagulant therapy.
175
A patient appears nervous before blood draw. What should you do?
Remain professional, reassure them, and help calm the patient.
176
PTT was previously normal, now it’s elevated. What should you do?
Verify with the nurse if the patient is on anticoagulant therapy.
177
A tissue specimen in formalin is received for culture. What should you do?
Reject the specimen.
178
A doctor wants to add a test to an 8-hour-old sample. Which test can still be performed?
Amylase (not time-sensitive).
179
Blood was drawn in EDTA and lithium heparin tubes, but the EDTA tube clotted. Which test will fail autoverification?
CBC.
180
What is the effect of a short draw in an INR test?
Prolonged PT result.
181
How do you identify a patient before collecting a sample?
Use the wristband.
182
You are about to collect blood from a patient who doesn’t have a wristband. What should you do?
Ask the nurse and patient for identity confirmation before proceeding.
183
A physician calls to add a test to a previously submitted sample. What must the technologist do?
Check the LIS for the sample’s date and time of collection.
184
Which of the following can result in hemolysis?
Using a needle with too small a diameter.
185
A female patient requests a female technician for blood draw. What should be done?
Comply with the patient’s request.
186
A dialysis center is established in the community. Which department will experience more workload?
Chemistry.
187
A CSF tube is received with multiple test requests. What should you do?
Ask the physician which tests to prioritize.
188
What is the main disadvantage of point-of-care testing (POCT)?
It is more expensive.
189
Before venipuncture, the patient expresses fear of needles but gives verbal consent. What should you do?
Proceed with venipuncture while the patient is lying down.
190
Which of the following specimens should be rejected?
Lithium heparin tube for viral culture.
191
A gastric biopsy is submitted for acid-fast bacilli detection. What is the correct specimen?
Gastric washings (not biopsy).
192
Stool is received in formaldehyde for Ova & Parasite exam. What should you do?
Accept the specimen (formalin is acceptable for O&P exams).
193
Which of the following specimens should be prioritized?
D. Blood gas.
194
Establish the correct priority for testing:
1. CSF from surgery patient
2. Blood culture from febrile patient
3. Hgb from surgery patient
4. C. perfringens – gas gangrene.
195
A patient with infectious TB has a sputum spill in the biosafety cabinet. Which solution should you use for cleanup?
C. 75% ethanol.
196
Which of the following should be stored in a flammable cupboard?
A. Acetone.
197
How is total magnification on a microscope calculated?
Eyepiece magnification × Objective magnification.
198
What condition is typically diagnosed using darkfield microscopy?
Syphilis.
199
What sample type is best observed using phase contrast microscopy?
Unstained living cells.
200
What is observed using polarized light microscopy?
Crystals, birefringence, synovial fluid.
201
A 1:10 diluted urine sample with 0.01 mL plated yields 86 colonies. What is the colony count in CFU/mL?
8.6 × 10⁷ CFU/L or 8.6 × 10⁶ CFU/mL
202
Which specimen requires a Staphylococcus streak for culture?
Conjunctival swab.
203
Which specimen is appropriate for diagnosing whooping cough?
Nasopharyngeal swab.
204
How much blood is needed to prepare 750 mL of 5% blood agar?
37.5 mL (750 mL × 0.05).
205
Which organisms are commonly implicated in human bite infections?
• Streptococcus anginosus (α-hemolytic, GPC in chains)
• Staphylococcus aureus (β-hemolytic, GPC in clusters)
• Eikenella corrodens (non-hemolytic, small GNR)
206
Which stain differentiates bacteria from dust?
Acridine Orange.
207
How do you visualize organisms present in low concentration within a specimen?
Acridine Orange stain.
208
If a slide coagulase test is negative, what is the next step?
Perform tube coagulase.
209
E. coli is identified by MALDI-TOF from selenite broth culture. What do you report regarding Salmonella and Shigella?
“No Salmonella or Shigella isolated.”
210
Pseudomonas aeruginosa is frequently associated with which patient population?
Cystic fibrosis patients.
211
Which medium is used to isolate organisms from cystic fibrosis patients?
Rogosa agar with CO₂ incubation and/or Mannitol Salt Agar for Staphylococcus.
212
Clostridioides difficile infection most commonly causes which condition?
Pseudomembranous colitis.
213
Which organism is the usual cause of subacute bacterial endocarditis?
Viridans group streptococci.
214
Which pathogen is a common cause of burn wound infections?
Pseudomonas aeruginosa.
215
What is the best stain for demonstrating acid-fast bacteria?
Ziehl–Neelsen (ZN) stain.
216
After methylene blue counterstaining in ZN, what color are Mycobacterium tuberculosis bacilli?
Red.
217
What color do Mycobacterium leprae bacilli appear in acid-fast stains?
Red.
218
What distinguishes the Kinyoun stain from the ZN method?
It is a “cold” acid-fast stain (no heating required) and still yields red mycobacteria.
219
A non-hemolytic, slide coagulase-negative Staphylococcus from a female urine specimen is most likely…
Staphylococcus saprophyticus.
220
You isolate catalase-positive, slide coagulase-variable, non-hemolytic GPC from urine. What should you do next?
Perform a novobiocin sensitivity test (to distinguish S. saprophyticus).
221
What is the atmospheric requirement for Bacteroides fragilis culture?
Anaerobic environment.
222
Which organism is most commonly associated with otitis media and sinusitis?
• Streptococcus pneumoniae (inner ear)
• Haemophilus influenzae (sinus)
• Moraxella catarrhalis (both)
223
You observe a colony with a metallic sheen on MacConkey agar. What test should you perform next?
Oxidase test.
224
What is the most cost-effective initial test for a throat swab?
Gram stain.
225
Which organism is the primary cause of bacterial vaginosis?
Gardnerella vaginalis.
226
Which feature helps differentiate E. coli O157 from Shigella species?
Motility ( E. coli is motile; Shigella is non-motile).
227
A fisherman presents with a wound infection. Which organism is likely?
Aeromonas species.
228
What should be done after identifying Plasmodium falciparum in a Wright-stained blood smear?
Perform parasitemia count (or call the physician if parasitemia isn’t an option).
229
Which antiseptic is ineffective against fungi?
Ethanol.
230
Klebsiella oxytoca is indole positive, and K. pneumoniae is indole negative. Where should colonies be taken from to perform the test?
Blood Agar Plate (BAP) or Sheep Blood Agar (SBA).
231
A fungal culture is negative after 5 days. What should be done next?
Incubate for 7 days (fungi grow slowly).
232
A blood culture is positive for gram-negative bacilli. What is the next step?
Call the physician or the ward.
233
Staphylococcus saprophyticus is best described as:
Novobiocin resistant.
234
Slide coagulase negative, tube coagulase positive. What is the correct report?
Report as Staphylococcus aureus.
235
Which organism is slide coagulase positive, tube coagulase negative, and PYR positive?
Staphylococcus lugdunensis.
236
Gram-positive cocci, catalase-negative, optochin-resistant, bile soluble positive, PYR negative. Likely organism?
Streptococcus pneumoniae.
237
What effect does a heavy inoculum have on zone size in disk diffusion testing?
Smaller zones.
238
What effect does a light inoculum have on zone size in disk diffusion testing?
Larger zones.
239
What is the bacterial concentration of a 0.5 McFarland standard?
1–3 × 10⁸ CFU/mL.
240
What is used to make a 0.5 McFarland standard?
Barium sulfate.
241
What is the drug of choice for treating Enterococcus faecalis in CSF?
Ampicillin.
242
What is the drug of choice for treating Escherichia coli in CSF?
Ceftriaxone.
243
Which is the drug of choice for treating sepsis caused by E. coli?
Ceftriaxone.
244
A Kirby-Bauer test for Streptococcus pneumoniae using oxacillin shows a 20 mm zone after 16 hours. What should be done next?
Incubate for 4 more hours (total 20–24 hrs required).
245
Which group of organisms are resistant to Nitrofurantoin?
Proteus species (PPM group: Proteus, Providencia, Morganella).
246
How should a β-lactamase-positive Haemophilus influenzae be reported in terms of ampicillin susceptibility?
Ampicillin resistant.
247
How should a β-lactamase-positive Neisseria gonorrhoeae be reported?
Penicillin resistant.
248
Which organism is non-motile and citrate negative?
Shigella sonnei.
249
What is the function of antibiotics in Modified Thayer-Martin (MTM) medium?
Suppress normal flora.
250
What is the most appropriate test for diagnosing bacterial vaginosis?
Wet mount and Gram stain.
251
Anaerobic organisms are often isolated as part of what type of culture?
Mixed culture.
252
What is the most common cause of a negative culture result in neonatal sepsis?
Inadequate blood volume collected.
253
What color does Mycobacterium tuberculosis appear after methylene blue counterstaining?
Blue (background), but AFB bacilli appear red.
254
What is the vector for Plasmodium spp. (malaria)?
Anopheles mosquito.
255
A urine sample submitted for C&S reveals four different colony types. What is the next step?
Report as mixed growth; assume contamination.
256
What should be done if Salmonella typhi does not react with antisera?
Boil the suspension and repeat the serotyping.
257
What organism causes impetigo?
Streptococcus pyogenes.
258
What organism is used as a negative control for the PYR test?
Streptococcus agalactiae.
259
What gram-positive bacillus might be seen in a urine culture?
Corynebacterium.
260
What is an economical method to identify Group A beta-hemolytic streptococci?
Subculture/isolation and identification.
261
A gram-negative intracellular diplococcus was isolated from sputum. What is it likely to be?
Moraxella catarrhalis.
262
Urea is normal but creatinine is high in a healthy patient. What should be done?
Repeat the test.
263
Which organism is unsuitable as an anaerobic control?
Bacteroides fragilis.
264
A staphylococcus isolate is negative in the tube coagulase test after 24 hours at 37°C. What is the next step?
Repeat tube coagulase at room temperature (22°C) for 24 hours.
265
What color does methylene blue turn in anaerobic conditions?
White.
266
What is the most critical step in Gram staining?
Decolorization.
267
What do pink cocci in chains suggest on a Gram stain?
Over-decolorization.
268
Among CSF, synovial fluid, and suprapubic urine, which should be processed first?
CSF.
269
How should Neisseria meningitidis be shipped?
At room temperature with CO₂.
270
How many sets of blood cultures are ideal within 24 hours?
2 sets or fewer.
271
What can cause a false positive oxidase test?
Using nichrome wire loops.
272
What can cause a false positive catalase test?
Picking the colony from blood agar.
273
When should the pH of media be measured?
Before pouring and before solidification.
274
What differentiates Vibrio species from Aeromonas and Plesiomonas?
Salt tolerance.
275
Which organism commonly causes endogenous infections in the mouth and gut?
Bacteroides fragilis.
276
Where should anaerobic cultures be used?
Surgical tissue.
277
An anaerobic blood culture is negative after 5 days. What should be done next?
Prepare an aerobic culture.
278
Which condition should be reported first: eye keratitis or gas gangrene?
Gas gangrene.
279
Vaginal smear shows Lactobacillus 2+ and Gardnerella vaginalis 3+. What does this indicate?
Normal vaginal flora.
280
What does MIC refer to?
The lowest concentration (last tube/well) where no bacterial growth is observed.
281
CSF shows low glucose. What condition does this suggest?
Bacterial meningitis.
282
Which organism demonstrates bipolar staining?
Yersinia pestis.
283
You encounter erroneous results in bacterial catalase controls. What should you do?
Repeat controls with clinical isolates.
284
An anaerobic bottle suspected of Candida albicans shows no growth after 5 days. What is the next step?
Prepare an aerobic culture.
285
Long, beaded, branching gram-positive bacilli isolated from sputum is likely what organism?
Nocardia.
286
A Gram stain from a positive blood culture bottle shows gram-positive cocci. What should be done first?
Call the physician to report the finding.
287
Two consecutive days show small zones in the Kirby-Bauer test. What is the likely reason?
Expired antibiotic discs.
288
What additional precaution should be taken with Bacillus anthracis?
Notify the receiving laboratory.
289
You identified Clostridium difficile in the hospital. What is the next step?
Call infection control.
290
You identified Staphylococcus aureus. What is the next step?
Call infection control.
291
A gram-positive cocci, catalase-negative, non-hemolytic organism is found. What is the next test?
Perform PYR test.
292
Optochin-resistant, bile soluble, mucoid, alpha-hemolytic organism is isolated. What is the organism?
Streptococcus pneumoniae.
293
Gram-negative diplococci are seen in CSF. What is the most abundant WBC?
Neutrophils.
294
Positive and negative controls for DNAse?
Serratia (positive), E. coli (negative).
295
A gram-positive cocci is slide coagulase-negative. What is the next step?
Perform tube coagulase.
296
At what temperature is Campylobacter incubated?
42°C.
297
At what temperature does Pseudomonas grow well?
42°C.
298
At which temperature is motility best observed for Yersinia?
25°C.
299
At what temperature should stool for C. difficile toxin be stored if not processed immediately?
-70°C.
300
At what temperature should a blood specimen for viral load be stored?
-20°C.
301
At what temperature is B. stearothermophilus incubated after autoclaving?
55°C.
302
At what temperature should synovial fluid be stored?
4°C.
303
Which antibiotic is used if S. pneumoniae is resistant to penicillin?
Oxacillin (for screening).
304
What zone size on oxacillin disc diffusion suggests resistance to penicillin in S. pneumoniae?
≤19 mm.
305
An oxacillin zone of 20 mm is observed after 16 hours of incubation. What is the next step?
Incubate for 4 more hours (needs 20–24 hours).
306
Optochin-resistant but bile soluble organism?
S. pneumoniae.
307
Alpha-hemolytic colonies, catalase-negative, optochin-resistant, and Na deoxycholate positive. What is the organism?
S. pneumoniae.
308
What organism causes otitis media and shows alpha hemolysis and mucoid colonies?
S. pneumoniae.
309
Describe Bacillus anthracis morphology and properties.
Gram-positive rods, catalase-positive, non-hemolytic, non-motile, boxcar-shaped, aerobic.
310
What biosafety cabinet is used when handling B. anthracis?
BSC Class II.
311
What causes whooping cough?
Bordetella pertussis.
312
Best specimen to detect B. pertussis?
Nasopharyngeal swab.
313
Most abundant cell in whooping cough?
Lymphocytes.
314
What information is important when detecting C. difficile?
Date of admission.
315
Most appropriate test for C. difficile?
Toxin detection.
316
What is the best specimen for Trichinella spiralis?
Muscle biopsy.
317
How is Trichinella spiralis transmitted?
Eating undercooked pork.
318
Yeast with blastoconidia, pseudohyphae, and chlamydospores on corn meal agar. What is the result?
Germ tube positive.
319
PYR for E. faecalis is positive; PYR for S. agalactiae is negative. What should be done?
Record and report patient results.
320
Which animals serve as reservoirs for Salmonella?
Reptiles and poultry.
321
What organism causes infection from a human bite?
Alpha-hemolytic streptococci (Streptococcus anginosus).
322
An anaerobic jar shows moisture and warmth, but the indicator remains blue. What is likely the problem?
Leak in the gasket.
323
Presence of malaria in a thin smear—what’s the next step?
Do a thick smear.
324
What causes false resistance in the Kirby-Bauer test?
Not swabbing the plate evenly.
325
No bacteria present in a heat-fixed Gram stain from a positive blood culture bottle. What is the next step?
Fix the smear using methanol.
326
What scenario should be reported to infection control?
Maltose-positive organism in CSF.
327
In a patient with whooping cough, which cell is most prominent?
Lymphocytes.
328
Cervical sample: Cytochrome oxidase negative, glucose positive, maltose/lactose negative. What’s the next step?
Report as N. gonorrhoeae.
329
How to differentiate between Aeromonas, Plesiomonas, and Vibrio?
Use salt broth.
330
What is the most common contaminant in urine cultures?
Coagulase-negative staphylococci (CONs).
331
Given the following zone diameters for vancomycin and ampicillin controls, how should the result for Enterobacter aerogenes be interpreted?
D) Repeat control with same organism (but ALSO apply interpretation rules):
✅ All Gram-negative organisms (including E. aerogenes) are intrinsically resistant to vancomycin regardless of zone size.
✅ E. aerogenes belongs to the SPICE group (Serratia, Pseudomonas, Indole-positive Proteus, Citrobacter, Enterobacter), and ampicillin must be reported as resistant for these organisms—even if zone size is large.
So the correct interpretation is:
Vancomycin = resistant (intrinsically)
Ampicillin = resistant (SPICE rule)
332
What should you do if PCR yields no product after 20 cycles?
Increase to 45 cycles.
333
What should you do if PCR yields no product after 25 cycles?
Increase to 45 cycles.
334
What should you do if PCR yields no product after 30 cycles?
Stop and report as negative.
335
What is used to decontaminate PCR work areas?
Uracil DNA glycosylase.
336
Why does G-C content increase DNA melting temperature compared to A-T?
G-C has three hydrogen bonds (more stable), while A-T has two.
337
Which is the correct order and temperature for a standard PCR cycle?
• Denaturation: 94–95°C (30 sec – 1 min)
• Annealing: 50–68°C (30 sec – 1 min)
• Extension: 72°C (1 min)
338
PCR was performed at 72–94–55°C for 20 cycles. What should be done?
Reset the cycle to the correct order: 94–55–72°C.
339
DNA failed to hybridize during PCR. What is the likely cause?
Reverse primer was not used.
340
Which enzyme is required to convert RNA to DNA?
Reverse transcriptase.
341
What happens if the PCR machine fails to reach 94°C?
DNA will remain double stranded (no denaturation).
342
How do you know when a PCR is complete in real-time PCR?
When the fluorescent signal threshold is reached.
343
Which base pairing is correct for RNA?
A–U, G–C.
344
Where is DNA and RNA located in a eukaryotic cell?
DNA is in the nucleus; RNA is in the cytoplasm.
345
PCR control is positive but the target is not detected. What is the likely cause?
Incorrect primer was used.
346
Which method is used to identify the presence and number of a gene in a genome?
Southern blot.
347
Where is nucleic acid produced in the cell?
DNA in the nucleus; RNA in the cytoplasm.
348
What volume of 50 mmol MgCl₂ is required to prepare a 2.4 mM master mix for ten 50 µL PCR reactions?
2.5 µL.
## Footnote
Using C₁V₁ = C₂V₂ → (50)(x) = (2.4)(500) → x = 2.4 × 500 / 50 = 2.4 µL ≈ 2.5 µL
