Laboratory Medicine Flashcards
Accuracy
How closely test results correspond to gold standard
Precision
How reproducible results are with repeat testing of same specimen
Specificity
% of persons without disease of interest with negative results.
(#pts w/o dz & - test)/(tot #pts w/o dz). Specific tests have fewer false positives; if result is positive, likely true. Used to rule in a disease (SPIN).
Sensitivity
% of persons with disease of interest with positive result.
(#pts w/ dz & + test)/(tot #pts w/ dz). Have fewer false negatives; if test negative, likely true. Used to rule out a disease (SNOUT).
False positive
Erronous test result that indicates presence of disease that does not exist
False negative
Erroneous test result that failed to recognize an existing disease
Prevalence
cases of disease in a population
Likelihood ratio (LR)
How likely test will be helpful.
>1: Test result assoc w/dz.
<1: Test result associated with absence of disease.
LR+: (prob of + test in pt w/dz)/(prob of + test in pt w/o dz)
LR-: (prob of - test in pt w/o dz)/(prob of - test in pt w/dz)
Predictive value (PV)
Estimation of probability of presence or absence of dz; derived from test’s sensitivity, specificity, and prevalence of dz in tested population.
PPV: %pts w/+ test w/dz
NPV: %pts w/-test w/o dz
Pre-test probability
Proportion of people in population at risk who have disease at certain time (prevalence); probability that pt has dz before test performed. (Ex: 2.8% probability of chlamydia in 15-19 YOF).
Post-test probability
Proportion of pts w/+ test who truly have dz; pt based probabilty of having dz. LR translates pre-test and post-test probability (via nomogram). (85% probability that chlamydia test is helpful in 15-19 YOF).
Discuss major reasons for odering a laboratory measurement
Discover occult disease - make dx
Confirm suspected dx
Differentiate b/t dx
Determine stage, activity, or severity of dx
Detect recurrence of dz
Assess effectiveness of therapy (BP readings)
Guide course of therapy
Pros/cons of profile or panel testing
Pros: Often less costly to group lab tests together.
Cons: Unnecessary pt data often generated.
Use most cost effective, sensitive and specific measures.
Significance of ordering STAT lab test and critical results
STAT: Rapid turnaround rate of results. Used in emergency situations where results needed immediately. Critical value (PANIC): Indicate potentially dangerous conditions which require immediate attention by clinician.
Describe CLIA (Clinical Laboratory Improvement Amendments) guidelines for “waived tests”
Those that pose no risk or harm to pt if used incorrectly or use such simple/accurate methodologies that inaccurate results are unlikely (fecal occult blood test).
Describe CLIA (Clinical Laboratory Improvement Amendments) guidelines for “provider performed microscopy tests”
Examination must be performed by physician or mid-level practitioner during pt visit. Primary instrument must be microscope.
Dipstick urinalysis
Plastic strip place in urine sample, chemical rxns change color on stick. Measures: pH, sp gravity, protein, sugar, ketones, bilirubin, blood, infection, blah, blah, blah.
Fecal occult blood testing
Tests for blood in stool. Applicable for: Colon CA, anemia, routine rectal exam, screening.
Urine pregnancy test
Urination on dipstick measures presence of hCG - a hormone produced by the placenta.
Erythrocyte sedimentation test
Used to detect inflammation, non-specific or diagnositic, can be used to monitor disease activity and response to therapy.
Spun hematocrit
Measurement of RBC count. Detects anemia.
Wet mount
Microscopic examination of vaginal discharge for bacterial vaginosis et al.
Potassium hydroxide mount
Microscopic examination keratinized structures or body fluids for fungal elements (does not determine species).
Pinworm prep
Clear tape applied to anal area in early AM. Eggs on skin surface will stick to tape, identified under microscope.
