Diagnostic Procedures Flashcards

According to CLSI order of draw, which tube or specimen is collected first?

Answer: Blood culture bottles

Sterile blood culture specimens are drawn first to avoid contamination, followed by citrate, serum, heparin, EDTA, and fluoride tubes.

Which agar is the standard medium for Kirby-Bauer disk diffusion susceptibility testing?

Answer: Mueller-Hinton agar

Mueller-Hinton agar is standardized for reproducibility, has low levels of inhibitors, and supports even antibiotic diffusion.

Why are group O reagent red cells used in the antibody screen?

Answer: They lack A and B antigens, so they will not react with anti-A or anti-B

Group O screening cells avoid ABO interference, so any agglutination points to unexpected antibodies to other antigens such as Rh, Kell, Duffy, or Kidd.

A negative D-dimer result is most clinically useful for what?

Answer: Helping rule out DVT or pulmonary embolism in low-probability patients

D-dimer has high sensitivity and negative predictive value, so a normal result helps exclude venous thromboembolism, while positive results are nonspecific.

Which tube additive best preserves glucose when a specimen cannot be processed promptly?

Answer: Sodium fluoride

Sodium fluoride in gray-top tubes inhibits enolase and stops glycolysis, which otherwise lowers glucose by about 5-7% per hour.

When collecting blood cultures for suspected bacteremia in adults, what is standard practice?

Answer: Two or more sets from separate venipuncture sites, each with aerobic and anaerobic bottles

Multiple sets from different sites increase detection and help tell true pathogens from skin contaminants.

When CSF is collected in three numbered tubes, tube 3 is typically sent to which department?

Answer: Hematology for cell counts

Tube 3 is least likely to contain cells from a traumatic tap, so it is used for cell counts, while tube 1 goes to chemistry and tube 2 to microbiology.