Laboratory Medicine

Question 1

Accuracy

Answer 1

How closely test results correspond to gold standard

Question 2

Precision

Answer 2

How reproducible results are with repeat testing of same specimen

Question 3

Specificity

Answer 3

% 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).

Question 4

Sensitivity

Answer 4

% 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).

Question 5

False positive

Answer 5

Erronous test result that indicates presence of disease that does not exist

Question 6

False negative

Answer 6

Erroneous test result that failed to recognize an existing disease

Question 7

Prevalence

Answer 7

cases of disease in a population

Question 8

Likelihood ratio (LR)

Answer 8

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)

Question 9

Predictive value (PV)

Answer 9

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

Question 10

Pre-test probability

Answer 10

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).

Question 11

Post-test probability

Answer 11

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).

Question 12

Discuss major reasons for odering a laboratory measurement

Answer 12

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

Question 13

Pros/cons of profile or panel testing

Answer 13

Pros: Often less costly to group lab tests together.
Cons: Unnecessary pt data often generated.
Use most cost effective, sensitive and specific measures.

Question 14

Significance of ordering STAT lab test and critical results

Answer 14

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.

Question 15

Describe CLIA (Clinical Laboratory Improvement Amendments) guidelines for “waived tests”

Answer 15

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).

Question 16

Describe CLIA (Clinical Laboratory Improvement Amendments) guidelines for “provider performed microscopy tests”

Answer 16

Examination must be performed by physician or mid-level practitioner during pt visit. Primary instrument must be microscope.

Question 17

Dipstick urinalysis

Answer 17

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.

Question 18

Fecal occult blood testing

Answer 18

Tests for blood in stool. Applicable for: Colon CA, anemia, routine rectal exam, screening.

Question 19

Urine pregnancy test

Answer 19

Urination on dipstick measures presence of hCG - a hormone produced by the placenta.

Question 20

Erythrocyte sedimentation test

Answer 20

Used to detect inflammation, non-specific or diagnositic, can be used to monitor disease activity and response to therapy.

Question 21

Spun hematocrit

Answer 21

Measurement of RBC count. Detects anemia.

Question 22

Wet mount

Answer 22

Microscopic examination of vaginal discharge for bacterial vaginosis et al.

Question 23

Potassium hydroxide mount

Answer 23

Microscopic examination keratinized structures or body fluids for fungal elements (does not determine species).

Question 24

Pinworm prep

Answer 24

Clear tape applied to anal area in early AM. Eggs on skin surface will stick to tape, identified under microscope.

Question 25

Capillary blood glucose

Answer 25

Drop of blood from finger prick placed on strip into glucometer. Used to monitor diabetes control.

Question 26

Ovulation test

Answer 26

Measurement of LH. Levels surge during ovulation, et al.