Laboratory Medicine Flashcards
anatomic pathology
The analysis of cellular and tissue morphology in tissue biopsy specimens
clinical pathology
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
The vast majority of clinical testing deals with ____.
The vast majority of clinical testing deals with clinical chemistry.
How point-of-care hCG tests work
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.
False positives on hCG point-of-care test
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
How point-of-care glucose tests work
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)
False readings on glucose point-of-care tests
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.
Reference range
The middle 95% of a distribution (mean +/- two standard deviations)
therapeutic range
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)
Direct measurement
Measuring the level of x metabolite in the blood when you want to know the level of x metabolite
Indirect measurement
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.
Optimizing Test Cutoff (Graph)
Screening tests want good ____, diagnostic tests want good ____.
Screening tests want good sensitivity, diagnostic tests want good specificity.
critical value
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.
Critical physiologic measures (e.g. serum sodium) have _____ distributions, while enzymatic biomarkers (e.g. liver enzymes) have _____ distributions.
Critical physiologic measures (e.g. serum sodium) have very tight Gaussian distributions, while enzymatic biomarkers (e.g. liver enzymes) have skewed distributions.
Phases of clinical labs
pre-analytical, analysis, and post-analytical.
Most recent studies of laboratory error have found that the most common source of error is _____.
Most recent studies of laboratory error have found that the most common source of error is pre-analytical
Interference
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
Spectral solutes which may interfere with analyte measurement by spectrophotometry
Hemoglobin (from hemolysis)
Bilirubin (Jaundice)
Hyperlipidosis (Lipemia)
Passive expert interpretation
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.
Active expert interpretation
Blood smear interpretation
Antibiotic resistance in bacteria
Clinical correlation of test results
Clinical “pages” with questions regarding unfamiliar tests
Order entry control
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.
CA125 Testing
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.
