Diagnostic Procedures Flashcards

Which coagulation test is primarily used to monitor patients on warfarin therapy?

Answer: Prothrombin time with INR

Warfarin depresses vitamin K-dependent factors (II, VII, IX, X), and the PT/INR is most sensitive to factor VII reduction.

What blood-to-anticoagulant ratio is required in a light blue (sodium citrate) tube for routine coagulation testing?

Answer: 9:1

Coagulation tubes must be filled to provide a 9 parts blood to 1 part 3.2% sodium citrate ratio for accurate results.

A hemoglobin A1c result reflects a patient's average blood glucose over approximately what period?

Answer: 2 to 3 months

HbA1c reflects glycemia over the roughly 120-day lifespan of red blood cells, weighted toward the most recent 2-3 months.

Which step of the Gram stain is most critical for correctly differentiating gram-positive from gram-negative organisms?

Answer: Decolorization with alcohol or acetone

Over- or under-decolorizing is the most common cause of Gram stain errors because it determines whether the crystal violet-iodine complex is retained.

Which cardiac biomarker is considered the most specific for myocardial injury?

Answer: Cardiac troponin I or T

Cardiac troponins are structural proteins specific to heart muscle and are the preferred biomarker for diagnosing myocardial infarction.

A direct antiglobulin test (DAT) is used to detect which of the following?

Answer: IgG or complement bound to red cells in vivo

The DAT detects in vivo sensitization of red cells, as seen in hemolytic disease of the newborn, transfusion reactions, and autoimmune hemolytic anemia.

The Westergren method is a standard procedure for measuring which test?

Answer: Erythrocyte sedimentation rate

The Westergren method measures how far red cells settle in a vertical tube in one hour, reported as mm/hr.