Intro to Lab Medicine

Question 1

Discuss the issues of infection control and Universal Precautions as they pertain to the performance of diagnostic testing

Answer 1

When running diagnostic tests such as blood draws, it is important to maintain sterility of the fluid being drawn as well as keeping the healthcare work safe from blood born pathogen exposures.

- Wear gloves when drawing blood
- Wash hands after drawing blood
- Wear eye protection 
- Wear a gown if there is a situation where there is a large amount of blood exposure

Question 2

Accuracy

Answer 2

How closely the test results correspond to the ‘gold standard’
How often is the test right?

Question 3

Precision

Answer 3

How reproducible the results are with repeat testing of the same specimen

Question 4

Specificity

Answer 4

Percent of persons without disease of interest with negative test results
SPIN
TP / TP + FN

Question 5

Sensitivity

Answer 5

Percent of persons with the disease of interest who have positive test results
SNOUT
TN / TN + FP

Question 6

Predictive Value

Answer 6

Estimation of probability of presence or absence of disease; derived from test’s sensitivity, specificity, and prevalence of the disease in the tested population

Question 7

Positive PV (PPV)

Answer 7

Percent of persons with positive test results who have the disease
TP / (TP + FP) x 100

Question 8

Negative PV (NPV)

Answer 8

Percent of persons with negative test who do not have the disease
TN / (TN + FN) x 100

Question 9

False Positive

Answer 9

Erroneous test result that indicates presence of a disease that does not exist

Question 10

False Negative

Answer 10

Erroneous test result that failed to recognize an existing disease

Question 11

Prevalence

Answer 11

Number of cases of disease in a population

Question 12

Likelihood Ratio

Answer 12

How likely the test is to be helpful

Question 13

+ LR

Answer 13

> 1; associated with the disease and is helpful to rule in

Sensitivity / 1 - Specificity

Question 14

• LR

Question 15

Pretest Probability

Answer 15

Proportion of people in population at risk who have the disease at a certain time
Probability the patient has the disease before test is performed

Question 16

Posttest Probability

Answer 16

Proportion of patients testing positive who truly have the disease
Patient based probability of having disease (likelihood ratio translates pretest into posttest)

Question 17

Significance of reference ranges (NONE)

Answer 17

• Reference Range: statistically derived numerical range for lab values based on a sample of individuals assumed to be healthy.
• Standard parameters for a reference range are +/- 2 SD
• Age, sex, and population groups can affect reference ranges significantly.

Question 18

Examples of affected reference ranges (NONE)

Answer 18

• Pediatric patients may have lower reference ranges due to physiological immaturity.
• Geriatric patients are difficult to establish a reference range because of their wide variety of health status and disease states. (Some reference ranges are unchanged, some are changed with no clinical significance, and some are changed with clinical significance)
• X-linked and autosomal enzyme deficiencies
• Sickle Cell

Question 19

Common sources of error that can affect the quality of lab tests

Answer 19

• Lab processing or equipment errors
• Deteriorated reagents
• Calibration errors
• Calculation errors
• Misreading results
• Mis-entry of data/other documentation errors
• Improper sample preparation
• Improper specimen handling- collection, transportation, refrigeration
• Time course of specimen collection

Question 20

Major reasons for ordering a lab measurement

Answer 20

Screen, Diagnose, Manage disease

Question 21

Labs to screen

Answer 21

Screen for treatable conditions in pre-symptomatic individuals

Question 22

Labs to Dx

Answer 22

Diagnose disease in symptomatic individuals
o Discover occult disease
o Confirm suspected Dx
o Determine stage, activity, severity of disease, or progression of disease
o Detect recurrence of disease

Question 23

Labs to manage

Answer 23

Manage disease in individuals already diagnosed
o	Guide the course of therapy
o	Assess effectiveness of therapy
o	Drug levels
o	Side effects

Question 24

Pros of profile testing

Answer 24

Often less costly to group lab tests together

Question 25

Cons of profile testing

Answer 25

Unnecessary patient data is often generated. You want to use the most cost effective, sensitive, and specific measures when deciding between panel or single test ordering. Panel selection: based on availability of panel and appropriate medical staff consultation.

Question 26

Significance of order STAT tests

Answer 26

• STAT tests = rapid turnaround rate of the results
• Used in emergency situations where the test result are needed immediately
• Given high priority in the lab

Question 27

Results that indicate PANIC or Critical values

Answer 27

STAT test results have a critical value (PANIC) meaning they indicate potentially dangerous conditions which require immediate attention by the clinician.

Question 28

CLIA

Answer 28

Clinical Laboratory Improvement Amendments

Question 29

CLIA Waived Tests

Answer 29

Those that pose no risk of harm to the patient if used incorrectly or use such simple and accurate methodologies that inaccurate results are unlikely

Question 30

CLIA Provider Performed Microscopy Test (PPM)

Answer 30

o Must be performed by a physician or a mid-level practitioner during the patient visit
o Moderate complexity category
o Primary instrument is a microscope
o Specimen must be labile (or delay in testing could compromise the accuracy of the test)
o Control materials are not available to monitor the entire testing process
o Limited specimen handling is required
o Examples: KOH preps, UA micro only, semen analysis, nasal smears

Question 31

Dipstick Urinalysis

Answer 31

• Strip is placed in the urine sample, chemical reactions cause color changes that are compared to a key
• Measures pH, specific gravity/concentration, protein, sugar, ketones, bilirubin, evidence of infection & blood

Question 32

Fecal Occult Blood Test

Answer 32

• Tests for stool in the blood, may indicate colon cancer
• Recommended annually after 50
• Positive result requires follow up colonoscopy)

Question 33

Urine Pregnancy Test

Answer 33

• Measure presence of hCG, hormone produced by the placenta
• Can be detected several days to two weeks after conception
• Positive result is confirmed with blood test

Question 34

Erythrocyte Sedimentation Test

ESR

Answer 34

• ESR, used to detect inflammation
• Non-specific or diagnostic
• Can be used to monitor disease and response to therapy

Question 35

Spun Hematocrit

Answer 35

• Measurement of RBC count (RBC should make up 37 – 49% of blood)
• Typically part of a CBC
• Used to detect anemia, not diagnostic

Question 36

Wet Mount

Answer 36

• Micro exam of vaginal discharge for bacterial vaginosis, candidiasis, trichomoniasis, increased WBC

Question 37

Potassium Hydroxide (KOH) mount

Answer 37

• Micro exam of skin, hair, nail, vaginal discharge, or body fluids for fungal elements
• Confirms presence, not species

Question 38

Pinworm prep

Answer 38

• Clear tape applied to anal area in early morning, eggs on skin surface will stick to tape and can be identified under microscope
• Should be done three days in a row

Question 39

Capillary Blood Glucose (CBG)

Answer 39

• Used to monitor diabetes control
• Drop of blood from finger stick is placed on a glucometer strip
• Values are used to determine insulin dose

Question 40

Ovulation Test

Answer 40

• Measurement of LH, levels surge during ovulation
• Monitored with menstrual irregularities, infertility, suspected menopause, low testosterone levels in males
• Can indicate developmental abnormalities in children