Diagnostic Procedures Flashcards

Which stain is used to perform a manual reticulocyte count?

Answer: New methylene blue

New methylene blue is a supravital stain that precipitates residual ribosomal RNA in living reticulocytes as a blue reticulum.

An in vitro hemolyzed specimen will most significantly and falsely increase which analyte?

Answer: Potassium

Red cells contain much more intracellular potassium than plasma, so hemolysis releases it and falsely raises results.

Which test is traditionally used to monitor unfractionated heparin therapy?

Answer: Activated partial thromboplastin time

Unfractionated heparin enhances antithrombin inhibition of intrinsic and common pathway factors, which prolongs the aPTT.

A gram-negative rod from a wound culture is oxidase-positive and gives off a grape-like odor. What is the most likely organism?

Answer: Pseudomonas aeruginosa

P. aeruginosa is an oxidase-positive nonfermenter with a characteristic grape-like odor, whereas Enterobacterales are oxidase-negative.

In a compatibility test, the immediate-spin crossmatch phase is mainly designed to detect what?

Answer: ABO incompatibility

Immediate-spin testing at room temperature detects IgM ABO antibodies that agglutinate incompatible donor cells directly.

Xanthochromia in a centrifuged cerebrospinal fluid supernatant most strongly suggests what?

Answer: Prior subarachnoid hemorrhage

A yellow supernatant comes from hemoglobin breakdown products after bleeding that occurred hours before collection, unlike a fresh traumatic tap.

On a urine reagent strip, specific gravity is measured by what principle?

Answer: pKa change of a polyelectrolyte with ionic concentration

Ions in the urine release hydrogen ions from a polyelectrolyte, and the resulting pH change shifts the indicator color (bromthymol blue).