Intro to Labs Flashcards
When should I order labs?
- Testing to confirm/ eliminate the presence of disease & improve cost-efficiency of screening tests
- Appropriate and thoughtfully-timed use will allow monitoring of dz and treatment
<10% of Dx is based on labs: expensive, takes time, invasive, sometimes wrong (requires more labs)
Why order labs?
- Establishing a Dx
- R/O a clinical condition
- *-MC: to monitor a clinical condition**
- To monitor a therapeutic intervention
- To establish prognosis
- To screen for dz (i.e. dyslipidemia)
- To confirm effective dosing, reduces chance of toxicity
Potential adverse effects
-Financial burden, physical harm, psychological harm, others
- **Financial: **immediate cost; insurance; occupational; legal
- **Physical: **minor pain/ hematoma at draw site; moderate: infection at draw site; major: inappropriate interpretation leading to mistreatment
- **Psychological harm: **= MC; medical office “PTSD;” Coumidin therapy: must F/U qweekly, then q2wks, then qmonthly
- **Others: **phlebotomist risk
Interpreting labs
- Must be interpreted with caution, taking into account all variables producing the results (every pt is different)
- Must consider this when comparing pt’s results to the test’s reference range
Reference Range
(not “normal range”)
- Binary result = yes or no (postive or negative)
- Reference range = interpreted w/in their context; defined by various factors (age, gender, race/ethnicity, pregnancy) -usually on labs sheets according to these factors
- Useful to get previous labs to compare as baseline
Normal reference range: +2SDs of average
Reference range questions
- Are test results outside of a reference range indicative of an underlying problem?
- Are test results inside of a reference range indicative of no problem?
- Not necessarily
- Not necessarily
- Results are suggestive, but not necessarily indicative of the presence or absence of a problem
- Interpret with caution & within the context of the pt’s background, presentation, historical findings, physical findings
Phlebotomy
- Knowing where to draw blood from
- Proper disposal of needles and sharps to avoid danger for ourselves & others; stabbing yourself when re-capping a needle is MC
Techniques to Prevent Hemolysis
- Mix all tubes with anticoagulant additives **gently **(vigorous shaking can cause hemolysis) 5-10 x
- Avoid drawing blood from a hematoma (cells are hemolyzed)
- If using needle & syringe, avoid drawing plunger back too forcefully (sheer force causes breakdown)
- Dry the venipuncture site before proceeding
- Avoid a probing, traumatic venipuncture (one of the MC reasons for hemolysis)
- Avoid prolonged tourniquet applications (< 2 min; < 1 optimal)
- Avoid massaging, squeezing, probing a site
- Avoid excessive fist clenching
- If blood flow into tube slows, adjust needle position to remain in the center of lumen
Blood Analysis
Fluid vs. cells
-Fluid: whole blood, serum, plasma
Plasma: 55% of total blood vol; 91% water, incl proteins like fibrinogen, albumin; nutrients; hormones; electrolytes
-Cells: RBCs, platelets, WBCs
Buffy coat = WBCs (7K-9K/mm3); platelets (250K/mm3) <1%
RBCs = 5 million/mm3 ~45% of total blood vol
Plasma vs. serum
Different tests require different processing of the
collected blood sample
- Plasma: liquid minus blood cells
- Blood collected in tube w/ anticoagulant, centrifuged to separate cellular portion; plasma is found at the top of tube
- Serum: plasma minus clotting proteins & cells
- Blood collected in tube w/o anticoagulant, allowed to clot, then centrifuged; serum is found at top of tube
-**Whole blood: **some tests e.g. CBC are performed on whole blood & analyzed w/o further processing
Basic Metabolic Profile
8 components
- *Electrolytes:**
1. Glucose
2. Calcium
3. Sodium
4. Potassium
5. CO2 (Carbon dioxide, bicarbonate)
6. Chloride - *Renal labs**:
1. BUN (blood urea nitrogen)
2. Creatinine
BMP
- Identify
- What is this missing?
A. Na (sodium)
B. Cl (Chloride)
C. BUN (Blood Urea Nitrogen)
D. Glucose
E. K (Potassium)
F. HCO3 (Bicarbonate)
G. Crt (Creatinine)
-Calcium not included in stick figure
Complete Metabolic Profile (CMP)
Include BMP + proteins, hepatic labs
- *Proteins**:
- Albumin (small protein produce in liver; major serum protein)
- Total protein (albumin + all other proteins)
- *Hepatic labs**
- Alkaline Phosphatase (ALP)
- Alanine amino transferase; SGPT (ALT)
- Aspartate amino transferase; SGOT (AST)
- Bilirubin
Liver Tests
A. AST
B. ALP
C. TBili
D. ALT
E. Albumin
CBC (one of the MC ordered)
9 components
Interpretation
- White blood cell count (WBC) w/ differential
- Red blood cell count (RBC)
- Hemoglobin (Hgb)
- Hematocrit (Hct)
- Mean Corpuscular Volume (MVC)
- Mean Corpuscular Hgb (MCH)
- Mean Corpuscular Hgb Concentration (MCHC)
- Platelet Count
- Red Cell Distribution Width
-Mildly abnormal CBCs should be intepreted cautiously & in comparison to pt’s past CBC results; 5% of healthy pts may have values out of normal range (repeat in few weeks to see trend if baseline isn’t available) vs. extremes which indicate pathology
Differential
-Bands, other types of leukocytes
- May not be included in a hemogram
- Usually automated to count cells ~32K; more accurate
- Manual can pick up unusual/atypical cells to clue into Dx e.g. cell “age” examined through size, structure of nuclear chromatin –> Band cells: immature neutrophils that are made in repair or reaction i.e. a major bacterial infection = left shift
- **Segmented: **more mature; likely d/t higher number of less mature bands (doesn’t differentiate b/n bands)
-Provides classification of WBC types present on sample: by size, staining activity
-Granulocytes: neutrophils, eosinophils, basophils
Agranulocytes: lymphocytes, monocytes,
CBC stick figure
*A. WBCs
B. Hemoglobin
C. Hematocrit
*D. Platelets
E. RBC Indices: MCV, MCH, MCHC, etc.
F. WBC Differential
*Some may switch WBCs and Platelets in figure
Granulocytes
-Function, increase/decrease
- *neutrophils: (polymorphonuclear lymphocytes, PMNs, polys) – most numerous; primary pathogen-fighting cells; contain phagocytic granules; less mature cells (bands**) indicate Left Shift
- Increase = acute bacterial infxn
- Decrease = viral infection
- *eosinophils:** granules contain major basic protein, enzymes & chemotactic factors; helps control allergic responses (asthma, hay fever), parasites = increase
- Decrease: severely stressed marrow (shock, severe burns); adrenal corticosteroids
- *Basophils: **release heparin, histamine & other inflammatory mediators (not phagocytic)
- Increase: hemolytic anemia (can occur with chicken pox & other conditions like basophilic (mast cell) leukemia & CML)
Agranulocytes
-Functions, increase/decrease
- *Lymphocytes: **2nd most numerous cell; B cells create antibodies, T cells control immune resp/ cell-mediated immunity; NK cells kill antigenic cells
- Increase: severe or chronic viral infections (e.g mononucleosis, CMV) ;chronic inflammatory conditions, ALL, CLL, lymphoma
- Decrease: AIDS primarily CD4 T cells; chemo; corticosteroids; malignancy
- *Monocytes:** phagocytic antigen-presenting cells/ create inflammatory mediators; first line of defense for some organisms & cells; helps remove damaged tissues, malignant cells, immunity against foreign substances
- Increase: malaria, endocarditis, typhoid fever, rocky mountain spotted fever; chronic inflammatory rxns, recovery from cell injury, nonhematopoietic malignancy
- **Decrease: **hairy cell leukemia
WBCs
“Never Let Monkeys Eat Bananas”
Neutrophils: most numerous (55-70%)
Lymphocytes: 20-40%
Monocytes: 2-8%
Eosinophils: 1-4%
Basophils: <1%
Low = leukopenia High = leukocytosis
RBCs
- **Hemoglobin: **measures total amt of Hgb in peripheral blood; rapid, indirectly measures RBC count
- **Hematocrit: **measures % of blood volume made up by RBCs; indirectly measures RBC # and volume, rapid measurement of RBC count
- **RBC count: **# of circulating RBCs in 1 mm3 of peripheral venous blood
- Anemia/ Polycythemia = low/ high of these 3 values
- **Mean Corpuscular Volume: **measurement of avg volume (size) of RBC
- Microcytic/Macrocytic = low/ high volume
- **Reticulocyte count: **indicates RBC production by bone marrow (ability to response to anemia & make more) if size/ shape varies widely, indication for manual diff
- Reticulocytopenia/ reticulocytosis = low/ high count
Morphology
**-Granulocytes with cytoplasmic organisms: **fungal/ bacterial infections
**-Reactive lymphocytes: **viral infections
**-Hypersegmented neutrophils: **pernicious anemia
**-Blasts, auer rods: **acute leukemia
-Hypochromic anemia presents as small, centrally pale RBCs; less heme = less ability to carry O2
