Lab Medicine Flashcards
(106 cards)
1
Q
4 Disciplines of Lab Medicine
A
- hematology
- chemical pathology
- microbiology
- immunology
2
Q
What types of clinical reasoning go into doing labs?
A
- why test is being ordered
- what are consequences of not ordering a lab test
- how good is the test at differentiating health from disease
- how are the test results interpreted
- how will the test results influence patient management
3
Q
Reference Range
A
- comparison of a patient’s laboratory test result vs. a reference or “normal” range
- for some analytes, the range is defined as less than or greater than a certain value
4
Q
What must be considered when using reference range to interpret a patient’s lab results?
A
- age
- gender (eg pregnancy if applicable)
- lab and technique used
- situational: geographic, fasting vs nonfasting, medications
5
Q
Gaussian Distribution
A
- a bell-shaped curve where the central 95% is typically used as a test’s normal range
- normal range encompasses mean plus or minus 2 SD
- roughly 5% of normal patients may be outside the cutoff value
6
Q
Screening Test
A
-identifies asymptomatic people who may have a disease
7
Q
Diagnostic Test
A
-determines presence or absence of disease when patient shows signs or symptoms
8
Q
What are some common disease screenings?
A
- pap smear for cervical cancer
- fecal occult blood test for colorectal cancer
- PSA tests for prostate CA
- PPD test screens for TB
- mammography for breast CA
9
Q
Validity
A
-how well a test distinguishes between who has disease and who does not
10
Q
Reliability
A
- consistency of test at different times or under different conditions
- degree to which results are free from random error
11
Q
Sensitivity
A
- measures validity of test
- disease oriented
- ability to identify those WITH disease correctly
- minimizes false negatives
- SNOUT: sensitivity test with negative results rules out disease
- # of true positives/(true positives + false negatives)
12
Q
Specificity
A
- healthy oriented
- ability to identify those without disease correctly
- minimizes false positive
- SPIN: specific test with positive result rules in disease
- # of true negatives/(true negatives + false positives)
13
Q
Principle Function of Circulating Blood
A
transportation
14
Q
Principle Function of RBCs
A
transport hgb, which carries O2
15
Q
Principle Function of WBCs
A
involved in defending your body from foreign invaders
16
Q
Principle Functions of Platelets
A
respond to blood vessel injury to form a clot
17
Q
Indications for Ordering a CBC
A
- investigate disease of blood or bone marrow
- investigate response to inflammation or infection
- assess sxs of fatigue, pallor, weakness, unexplained bleeding or bruising, dizziness, fever, weight loss
18
Q
What components are included in CBC?
A
- WBC count
- RBC count
- Hgb
- Hematocrit
- MCH, MCHC, MCV
- RDW
- platelets
19
Q
Normal RBC Range
A
- male 4.73 - 5.49 10^6/ uL
- female 4.15 - 4.87
20
Q
Mean Cellular Volume
- Normal Value
- Define
A
- 78-98 um^3
2. average volume of RBCs; useful in classifying type of anemia
21
Q
- Increase in Mean Cellular Volume
2. Decrease in Mean Cellular Volume
A
- increase MCV = vitamin B12 or folic acid deficiency
2. decrease MCV = iron deficiency anemia
22
Q
Hemoglobin
A
- male: 14.40 - 16.60 gm/deciliter
- female: 12.2 - 14.7 gm/deciliter
23
Q
Hematocrit
A
- proportion of blood that is made up of RBCs
- percentage of RBC/total blood volume
- men 40-54%
- women 37-47%
24
Q
Causes of Elevated Hgb
A
- loss of plasma volume (dehydration)
- high altitude
- smokers with COPD
- congenital heart disease
25
Causes of Low Hgb
- increased destruction of RBCs
- decreased production of RBCs
- blood loss
- pregnancy
- vitamin deficiency
26
WBCs
-normal: 4500-11000 cells/mm^3
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1. Granulocytes
| 2. Agranulocytes
1. neutrophils, eosinophils, basophils
| 2. lymphocytes, monocytes
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Neutrophils/PMN
- 40-76%
| - elevated in bacterial infections, inflammatory conditions
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Basophils
- 0-1%
- elevated CML, after splenectomy, polycythemia
- decreased rheumatic fever, pregnancy, steroid therapy, radiation therapy
30
Eosinophils
- elevated with allergic or parasitic infection, skin disease
- NAACP: neoplasma, allergy/asthma, Addisons disease, collagen vascular disease, parasites
31
Lymphocytes
- 24-44%
| - elevated with viral infection
32
Monocytes
- 3-7%
| - elevated with phagocytosis bacterial infections
33
Causes of Elevated WBCs
- acute bacterial or viral infections
- leukemia
- post splenectomy
- steroids (prednisone)
- may occur w/o disease: high stress, excitement, pain, trauma, heat)
34
Causes of Low WBCs
- viral infections
- overwhelming bacterial infections
- hypersplenism
- medications that suppress bone marrow
- bone marrow suppression
35
Platelets
- 150,000-400,000/mm^3
| - avg life span 7-10 days
36
Causes of Low Platelets
- enlarged spleen
- platelet destruction
- decreased platelet production
- alcoholism
37
Causes of Elevated Platelets
- hemorrhage
- splenectomy
- inflammation
38
Urinalysis
- assist in identifying urologic conditions: stone, UTI, malignancy
- assist in identifying systemic disease
- midstream, clean catch
39
Urinalysis: Clarity
-cloudy: bacteria, blood, crystals
40
Urinalysis: Odor
- foul smell with infection (e. coli)
| - sweet smell with diabetes (ketones)
41
Urinalysis: Color of Urine
- red: hematuria, kidney stones, UTI, bladder cancer
- yellow: dehydration, foods
- orange: medication side effects
- brown: glomerulonephritis, myoglobin
42
Specific Gravity
- 1.001-1.035
- elevated with volume depletion
- decreased with excessive fluid intake, diabetes insipidus, diuretic therapy
43
pH
- 4.6-8.0
- increased with vomiting, some urinary disease, or kidney disease
- decreased with aspirin overdose, starvation, alcohol ingestion, high protein diet
44
Urinalysis - Protein
- proteins too large to pass through glomerulus
| - associated with glomerulonephritis, pre-eclampsia, screen for complications from DM
45
Urinalysis - Glucose
- serum levels above 150-300 will produce glucose in urine
| - associated w/ DM, burns, pancreatitis, corticosteroid use, Cushing's disease
46
Urinalysis - Ketones
- ketones formed from breakdown of stored fat
| - associated with starvation, alcoholism, or diabetic ketoacidosis
47
Urinalysis - Bilirubin
- by-product of hemolysis
| - associated w/ biliary obstruction and liver injury
48
Urinalysis - Blood
-associated w/ kidney stones, urinary trauma, UTI, strenuous exercise or bladder cancer
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Urinalysis - Leukocyte Esterase
- detects enzymes released by WBCs
| - associated with UTI
50
Urinalysis - Urobilinogen
- bilirubin may react with bacteria in gut to produce urobilinogen
- associated w/ hemolysis and hepatocellular disease
51
Urinalysis - Nitrites
- some bacteria convert nitrates to nitrites
| - positive result = UTI usually
52
Microscopic Urinalysis Exam
- urine microscopic requires centrifuged sample
- requires lab tech to look for WBC, RBC, proteins, casts
- WBC: 0-5 per high power field
- RBC: 0-3 per high power field
53
Microscopic Urinalysis - Proteins
-associated w/ multiple myeloma
54
Microscopic Urinalysis - Crystals
- formed from solutes in the urine
| - associated w/ kidney stones
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Microscopic Urinalysis - Casts
- formed in distal convoluted tubule
- abnormal protein formed during infection of inflammation
- red cast: glomerulonephritis
- white cast: pyelonephritis
56
Liver Functions
- conjugate bilirubin
- synthesis of proteins and clotting factors
- involved in storage and disposal of nutrients, drugs, toxins
57
Liver Profile - Aspartate Aminotransferase
- 7-42 IU/liter
| - elevated with liver, muscle, or cardiac injury
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Liver Profile - Alanine Aminotransferase
- 1-45 IU/liter
| - more sensitive with liver injury
59
Liver Profile - Alkaline Phosphatase
- normal 25-160 IU/L
| - elevated with bile duct obstruction (cholecystitis, viral hepatitis, cirrhosis)
60
Liver Profile - Gamma glutamyl transpeptidase
- elevated with liver injury or biliary obstruction
| - used as a marker of alcohol use
61
Unconjugated Bilirubin
- bilirubin bound by albumin
- not water soluble
- elevated with hemolysis
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Conjugated Bilirubin
- bilirubin cleaved of albumin
- water soluble
- elevated with bile duct obstruction
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Albumin
- protein made in liver
| - marker of liver function
64
Indications for Ordering Coagulation Studies
- unexplained bleeding disorder or excessive bruising
- consecutive pregnancy loss
- patients receiving heparin or coumadin therapy
65
Prothrombin Time (PT)
- normal 11.5-13.5 seconds
- measure extrinsic pathway of coagulation
- time required for coagulation to occur
- marker of liver function
66
Partial Thromboplastin Time (aPTT)
- normal 27-38 seconds
- measures intrinsic coagulation pathway
- most commonly used to monitor heparin therapy
67
Pancreas Enzymes
amylase and lipase
68
Increased Levels of Amylase and Lipase Associated With?
- pancreatitis
- biliary obstruction
- pancreatic carcinoma
69
Amylase
- 10-130 U/L
| - peaks earlier and declines more rapidly with pancreas inflammation
70
Lipase
- normal < 52 U/L
- lipase remains elevated longer
- lipase more specific for pancreatic inflammation
71
Electrolyte Function
- determine overall fluid status
| - acid/base status
72
Indications for Ordering Electrolytes
- patients receiving IV fluid
- metabolic or endocrine abnormalities
- medications that interfere with electrolytes
- severe vomiting/diarrhea
73
Sodium
- 136-145 mmol/L
- major extracellular cation
- involved with maintenance of blood and body fluids and conduction of impulses
74
Elevated Sodium
- not enough water in body (dehydration)
- vomiting and diarrhea
- endocrine
75
Decreased Sodium
- overhydration
| - endocrine (Cushing's)
76
Potassium
- 3.5-5.0 mEq/L
- major intracellular cation
- involved in conduction of impulses
77
Elevated Potassium
- cell injury
- kidney failure
- endocrine (Addisons)
- can lead to arrhythmias
78
Decreased Potassium
- malnutrition
- vomiting, diarrhea
- diuretic medications
79
Elevated Chloride
- >107 mEq/L
- dehydration
- overactive parathyroid glands
80
Decrease Chloride
- <97 mEq/L
| - vomiting
81
Elevated Magnesium
- normal 1.3-2.1 mg/dL
- kidney disease
- use of antacids
82
Decreased Magnesium
- inadequate absorption (poor diet, alcoholism, diarrhea)
| - medications like diuretics
83
Calcium
- normal 8.2-10.2 mg/dL
- most stored in bone 99%
- half in circulation is protein bound, other half ionized
- only ionized Ca is metabolically active
- important in muscle contraction, cardiac function, nerve impulse, blood clotting
84
Elevated Calcium
- hyperparathyroid hormones
- cancer
- excessive vitamin D
85
Decreased Calcium
- hypoparathyroid hormones
- deficient protein
- vitamin D deficiency
86
Glucose
- formed from carb digestion and conversion of glycogen to glucose by the liver
- insulin decreases blood glucose
- glucagon increases blood glucose
- fasting blood glucose (<110, impaired 110-125)
- elevated glucose may be sign of DM, endocrine disorders, prednisone therapy, pancreatitis
87
Hgb A1C
- normal <5%
- measures glycosylated hemoglobin
- reflects the average blood glucose [ ] over past 2-3 months
- useful in monitoring DM management
88
Blood Urea Nitrogen (BUN)
- normal 5-20 mg/dL
- urea is produced in liver as waste from protein breakdown
- urea has to be filtered by the kidneys and is excreted in urine
89
Elevated BUN
- impaired kidney function
- increased protein catabolism
- dehydration
90
Decreased BUN
- liver failure (less urea produced)
- malnutrition
- endocrine disorders
91
Creatinine
- normal 0.9-1.2 men and 0.6-1.1 women
- production is constant and correlates directly with muscle mass
- assesses renal function
92
Elevated Creatinine
- impaired renal function
| - large muscle mass
93
Decreased Creatinine
- decreased muscle mass
| - liver disease
94
Uric Acid
- normal 3.4-8.0 mg/dL men, 2.4-6 women
- end product of purine metabolism
- most uric acid is excreted by the kidneys
95
Increased Uric Acid
- excessive cell breakdown of nucleonic acids (gout)
- excessive destruction of cells (leukemia)
- inability to excrete uric acid (renal failure)
96
Thyroid Gland
- regulates metabolic activity
| - involves interaction between hypothalamus, anterior pituitary, thyroid gland
97
TSH
- 0.4-4.8 mIU/L
- most sensitive test for screening thyroid disorders
- elevated = hyperthyroid
- decreased = hypothyroid
98
1. T4
| 2. T3
1. 0.8-1.7 ng/dL
2. 80-200 ng/dL
elevated T4/T3 = hyperthyroid
decreased T4/T3 = hypothyroid
99
Cultures
- involve growing microorgs or living tissue cells on a special medium to support growth of the material
- allow specific microbial identification
- collected and performed prior to beginning abx therapy
100
Blood Culture
-when suspected bacteremia present
101
Urine Culture
-when suspected UTI or pyelonephritis
102
Throat Culture
-gold standard for strep pharyngitis
103
Sputum Culture
-dx and tx of pneumonia and TB
104
Sed Rate
-marker of inflammation
105
D-dimer
- marker of clotting process
| - useful to screen for venous thrombosis (DVT)
106
Brain Natriuretic Peptide (BNP)
- hormone produced by ventricles of the heart
- increased with ventricular volume expansion and pressure overload
- increased with CHF
