Laboratory Medicine

Question 1

anatomic pathology

Answer 1

The analysis of cellular and tissue morphology in tissue biopsy specimens

Question 2

clinical pathology

Answer 2

The analysis of “liquid” specimens (blood, urine, and other bodily substances) – generally using chemical and physical methods, rather than visual inspection – to obtain information relevant to diagnosis and therapy

Question 3

The vast majority of clinical testing deals with ____.

Answer 3

The vast majority of clinical testing deals with clinical chemistry.

Question 4

How point-of-care hCG tests work

Answer 4

Urine is applied to a test strip and migrates through a membrane, where the antibody is bound. If hCG is present, it will complex with the antibody to produce a colorimetric reaction

Usually, both a monoclonal and a polyclonal antibody are used.

Question 5

False positives on hCG point-of-care test

Answer 5

hCG tests can give false positive results if the patient has an hCG-secreting tumor or if the urine sample is dilute, contains excess protein or lipid, or has significant turbidity

Question 6

How point-of-care glucose tests work

Answer 6

Blood glucose measurement is an example of an enzymatic assay, in which the molecule being detected (in this case, glucose) undergoes a chemical reaction that either produces a colorimetric product (most older instruments) or an electric current that can be measured (most modern instruments)

Question 7

False readings on glucose point-of-care tests

Answer 7

Point-of-care glucose finger prick tests have a mean 10% below that of the lab-determined mean and have a coefficient of variation of 20% as opposed to the lab coefficient of variation of 3%.

Remember, coefficient of variation is the standard deviation over the mean.

Question 8

Reference range

Answer 8

The middle 95% of a distribution (mean +/- two standard deviations)

Question 9

therapeutic range

Answer 9

For a particular drug.

Refers to the range of bioavailability at which the drug has therapeutic effects (above x) but no or minimal toxicity effects (below y)

Question 10

Direct measurement

Answer 10

Measuring the level of x metabolite in the blood when you want to know the level of x metabolite

Question 11

Indirect measurement

Answer 11

Measuring the level of y metabolite in the blood when you want to know the level of x metabolite, or y parameter as a proxy for x metabolite.

Question 12

Optimizing Test Cutoff (Graph)

Answer 12

Question 13

Screening tests want good ____, diagnostic tests want good ____.

Answer 13

Screening tests want good sensitivity, diagnostic tests want good specificity.

Question 14

critical value

Answer 14

A critical value is a low or high laboratory value that indicates a potentially life-threatening state in a patient

Reporting of critical values is tracked as a quality-assurance measure at most hospitals, and failing to report a critical value in a timely manner can result in legal liability.

Question 15

Critical physiologic measures (e.g. serum sodium) have _____ distributions, while enzymatic biomarkers (e.g. liver enzymes) have _____ distributions.

Answer 15

Critical physiologic measures (e.g. serum sodium) have very tight Gaussian distributions, while enzymatic biomarkers (e.g. liver enzymes) have skewed distributions.

Question 16

Phases of clinical labs

Answer 16

pre-analytical, analysis, and post-analytical.

Question 17

Most recent studies of laboratory error have found that the most common source of error is _____.

Answer 17

Most recent studies of laboratory error have found that the most common source of error is pre-analytical

Question 18

Interference

Answer 18

A type of analytical error in which an additional substance in the sample tested (other than the analyte itself) prevents accurate measurement.

Especially common with spectrophotometric assays

Question 19

Spectral solutes which may interfere with analyte measurement by spectrophotometry

Answer 19

Hemoglobin (from hemolysis)

Bilirubin (Jaundice)

Hyperlipidosis (Lipemia)

Question 20

Passive expert interpretation

Answer 20

With passive expert interpretation, test selection and reporting are performed automatically, without direct input from the clinician.

When ordered, laboratory physicians will determine the most appropriate tests, based on the patient’s history, and interpret and report the results.

Question 21

Active expert interpretation

Answer 21

Blood smear interpretation

Antibiotic resistance in bacteria

Clinical correlation of test results

Clinical “pages” with questions regarding unfamiliar tests

Question 22

Order entry control

Answer 22

Laboratory physicians (clinical pathologists) also intervene (passively or actively) at the level of test ordering to prevent ordering errors, ensure that tests ordered are appropriate to the clinical indication, and eliminate excessive testing.

Question 23

CA125 Testing

Answer 23

CA125 is a high molecular weight glycoprotein, which is expressed by a large proportion of epithelial ovarian cancers. Detected by the OC125 monoclonal antibody.

Demonstrated to have a high false positive rate and poor sensitivity/specificity. Also misutilized to a shocking extent, with 6% of patients receiving the test being male and only 36% actually being indicated for possible ovarian cancer.