Clinical Laboratory Medicine Flashcards
What is the purpose of all lab testing?
To reduce clinical uncertainty
What % of the population is abnormal but free of disease?
5%
What are more likely to cause incorrect results: clerical errors or technical errors?
Clerical errors
Define sensitivity.
The proportion of people with a disease who have a positive test result.
(If the person has the disease, a highly sensitive test will find it)
When a highly sensitive test provides a negative result, can you rule out the diagnosis?
Yes
What is an example of a highly sensitive test?
D-dimer
If -, can rule out pulmonary embolus
If +, cannot rule in the diagnosis
Define specificity.
The proportion of people without disease who have a negative result.
If a highly specific test provides a positive result, can you rule in the diagnosis?
Yes
What tests are included in a CBC?
RBC Hgb Hct WBC MCV MCH MCHC RDW
If collecting a CBC with differential, what information is added?
Neutrophils Bands/Segs Lymphocytes Monocytes Eosinophils granulocytes Basophils granulocytes
What would elevated neutrophils indicate?
Bacterial infection
What would elevated bands/segs indicate?
An active infection (shift to the left)
What would elevated lymphocytes indicate?
Viral infection
What would elevated eosinophil granulocytes indicate?
Allergic/hypersensitivity reactions
Parasitic infections
What is the normal range for WBCs?
4000-10,800
What is the normal range for Hgb?
14-18 g/dL men 13&up
12-16 g/dL women 13&up
What is the normal range for Hct?
42-54% men 13&up
36-48% women 13&up
What is the normal range for Plt?
140,000-400,000
What tests are included in a Chem 7?
Na+ K+ Cl- HCO3 BUN Creatinine Glucose
When would you want to test glucose levels?
To diagnose diabetes, hypoglycemia
When would you want to test Na+ levels?
To diagnose dehydration and overhydration
To evaluate water balance
When would you want to test K+ levels?
To diagnose hyper/hypokalemia
When would you want to test Cl- levels?
To assess electrolyte, acid-base, and water balance along with Na+, K+, and CO2
When would you want to test HCO3?
To assess acid-base balance
When would you want to test BUN?
To assess renal function since it is cleared by the kidneys
When would you want to test Creatinine?
To assess renal function since it is cleared by the kidneys
What are other instances that would elevate BUN besides renal insufficiency?
Dehydration
Upper GI bleeds
What is the normal BUN/creatinine ratio?
10:1
What would a BUN/creatinine ratio of >20:1 indicate?
A pre-renal issue
What would a BUN/creatinine ratio of <10:1 indicate?
A renal issue
What tests are included in a coag panel?
Partial Thromboplastin Time (PTT) Prothrombin Time (PT) / INR
When would you order a PTT?
To monitor heparin therapy’s effect on the intrinsic pathway (factors I, II, V, VIII, IX, X, XI, XII)
When would you order a PT/INR?
To monitor Coumadin therapy’s effect on the extrinsic pathway (factors I, II, V, VII, X)
What information can you get from a macroscopic urinalysis?
Color (pale-dark yellow normal)
Turbidity (clear is normal)
What information can you get from a dipstick chemical analysis?
pH Specific gravity Protein Glucose Ketones Nitrite Leukocyte esterase
What is normal pH of urine?
4.5-8.0
What is normal specific gravity of urine?
1.022-1.035
What does a specific gravity of <1.022 after 12 hours without food or water indicate?
Renal concentrating ability is impaired
What does a specific gravity of >1.035 indicate?
May contain high levels of glucose
Pt may have recently had IV dye
What is normal protein of urine?
<150mg/24 hours
What does protein of >3.5grams/24 hours indicate?
Nephrotic syndrome
What is the indicator dye used for protein detection?
Bromphenol blue
How much filtered glucose appears in the urine?
<0.1%
What does glucosuria indicate?
Diabetes mellitus
What do ketones in the urine indicate?
Breakdown of protiens
Diabetic ketosis
Calorie deprivation
What do nitrites in the urine indicate?
Bacteria in the urine, usually from gram negative rods
What does leukocyte esterase in the urine indicate?
Presence of WBCs
What needs to be ordered following a positive nitrite test?
24 hour urine for protein
What needs to be ordered following a positive leukocyte esterase test?
Microscopic evaluation with culture
What can be seen in a low power field (lpf) microscopic urinalysis?
Crystals
Casts
Squamous cells
What can be seen in a high power field (hpf) microscopic urinalysis?
Crystals
Cells
Bacteria
What is an abnormal amount of RBCs in the urine?
> 1 RBC/hpf
What could cause hematuria?
Glomerular damage Tumors Kidney trauma Kidney stones UTI Menstruation
What do you know about the concentration of urine if RBCs appear swollen?
Urine is dilute
What do you know about the concentration of urine if RBCs appear cratered?
Urine is concentrated
What could dysmorphic RBCs indicate?
Glomerular disease
What is pyuria, and what does it usually indicate?
WBCs in the urine
upper/lower UTI or acute glomerulonephritis
What is an abnormal number of WBCs in the urine?
> 2 WBCs/hpf
What does elevated epithelial cells int he urine indicate?
Nephrotic syndrome or tubular degeneration
What could squamous epithelial cells indicate?
Contamination
What creates casts, and where are they formed?
Protein denaturation and precipitation
In the distal tubule or collecting duct
What are some factors that favor cast formation?
Low flow rate
High salt concentration
Low pH
When are hyaline casts seen?
In healthy patients
What do RBC casts indicate?
Glomerulonephritis
Severe tubular damage
What do WBC casts indicate?
Acute pyelonephritis
Glomerulonephritis
What is a granular cast?
A cellular cast that remained in the nephron for some time before it was flushed out
When are broad casts seen, and where do they come from?
In end stage renal disease
They come from damaged and dilated tubules
What is the most common type of yeast seen in routine labs?
Candida
What types of crystals can be seen even in healthy people?
Calcium oxalate
Triple phosphate
Amorphous phosphates
How quickly does a clean-catch urine specimen need to be evaluated?
Within 1 hour of collection
What will happen to the specimen as time elapses prior to evaluation?
Decreased clarity Increase in pH Loss of ketone bodies Dissolution of cells and casts Overgrowth of contaminating microorganisms
When are cardiac enzymes released into the blood?
After necrosis of myocardial cells
When does troponin begin to rise?
2-6 hours after injury
Is troponin sensitive or specific for cardiac injury?
Specific
How long does TnI stay elevated?
5-10 days
How long does TnT stay elevated?
5-14 days
What are the 3 kinds of creatine kinase?
CK-MB (myocardium)
CK-MM (skeletal muscle)
CK-BB (brain)
What causes elevated CK levels?
MI Trauma Physical exertion Post-op state Convulsions
When does CK rise?
4-6 hours after injury
After how long does CK return to normal?
3-4 days
If CK-MB is elevated, but not CK-MM or CK-BB, what is probably the cause?
Heart injury (MI)
If CK-MM or CK-BB is elevated but not CK-MB, what is probably the cause?
A non-heart related issue
How does CK-MB differ from -MM and -BB?
Rises in 4-6 hours and returns to normal in 2 days
What causes the release of myoglobin?
Injury to striated muscle in skeletal or cardiac muscle
When does myoglobin rise?
2 hours after MI
When does myoglobin peak?
6-8 hours after MI
What can cause false myoglobin positives?
Skeletal muscle injury
Renal failure
What tests are included in a lipid panel?
Total cholesterol
Triglycerides (LDL, VLDL)
HDL
LDL
Why would you order a lipid panel?
To monitor risk for CAD
When are triglyceride levels the lowest?
In the morning
What is optimal for triglycerides?
<150
What can affect triglyceride test results?
What the patient ate the day before
What is optimal for HDL levels?
> 32 mg/dL in men
>38 mg/dL in women
What is optimal for LDL levels according to ATP III?
<100 mg/dL
What is desirable for total cholesterol levels according to ATP III?
<200 mg/dL
What tests are included in the Arterial Blood Gases respiratory labs?
pH PO2 PCO2 HCO3- SaO2
Why would you order ABGs?
To obtain information on respiration and kidney function
What is normal pH in the human body?
7.35-7.45
What type of compensation is occurring if the unaffected system is attempting to compensate but pH is not within normal range?
Partial compensation
What type of compensation is occurring when the unaffected system compensates to a nearly normal pH?
Complete compensation
What is normal PO2?
Newborn: 40-70 mmHg
Child/Adult: 80-100 mmHg
Age 60-90: 60-80 mmHg
What levels represent the respiratory component?
PCO2
What is normal PCO2?
35-45 mmHg
What levels represent the metabolic component?
HCO3-
What is normal HCO3-?
22-28 mEq/L
What is normal SaO2?
> 90%
What can cause inaccurate SaO2?
Dyshemoglobinemias
What is carboxyhemoglobin?
CO bound to hemoglobin
CO has 200 times the affinity for hemoglobin than does O2
What PO2 indicates hypoxia?
<60 mmHg
What PCO2 indicates alkalosis?
<35 mmHg
What PCO2 indicates acidosis?
> 45 mmHg
What HCO3- indicates acidosis?
<22 mEq/L
What HCO3- indicates alkalosis?
> 28 mEq/L
What tests are included in a sputum evaluation?
Gram stain
Bacterial culture
Acid-fast culture (for TB)
What would a sputum evaluation show if the patient provided a spit sample instead of sputum?
A lot of squamous epithelium
Describe characteristics of transudative effusion and what causes it.
Watery solution due to increased hydrostatic pressure or low oncotic pressure in the capillaries
Describe characteristics of exudative effusion
Fluid rich in protein and cellular elements that oozes out of vessels due to inflammation and permits passage of large molecules and solid matter through vessel walls
What specific gravity, protein, and PF/serum ratio indicate transudate effusion?
SG <0.5
What specific gravity, protein, and PF/serum ratio indicate exudate effusion?
SG >1.016
Protein >3.0
PF/serum >0.5
What WBC, RBC, and glucose indicate transudate effusion?
WBC <1000
RBC Few
Glucose = to serum
What WBC, RBC, and glucose indicate exudate effusion?
WBC >1000
RBC Variable
Glucose <serum
What cholesterol, pH, and appearance of urine indicate transudate effusion?
Cholesterol <55
pH 7.4-7.5
Clear
What cholesterol, pH, and appearance of urine indicate exudate effusion?
Cholesterol >55
pH 7.35-7.45
Cloudy
If cytology or amylase come back positive, what can you conclude?
Malignancy
Pancreatic (+ amylase)
