AACC AACC Specimen Collection & Processing 3

Question 1

What is the purpose of the serum separator tube (SST) gel in a gold or tiger-top tube?

Accepted Answer

To form a physical barrier between the clot and serum after centrifugation

Answer

The thixotropic gel in SST tubes migrates during centrifugation to form a stable barrier between the clot and serum, preventing analyte exchange and enabling easy serum harvest.

Question 2

When performing a 24-hour urine collection for creatinine clearance, what instruction is most critical for the patient?

Accepted Answer

Discard the first morning void, then collect all urine for the next 24 hours, ending with the next day's first void

Answer

Proper 24-hour collection begins by discarding the first morning void (to establish a clean start point) and ends with collecting the void exactly 24 hours later.

Question 3

What is the clinical significance of detecting bilirubin crystals (bilirubin precipitate) in a urine sample?

Accepted Answer

Suggests hepatobiliary disease, as conjugated bilirubin is filtered by the kidneys only when elevated in plasma

Answer

Conjugated (direct) bilirubin is water-soluble and filtered by the glomerulus when plasma levels are elevated, indicating liver disease, biliary obstruction, or hepatitis.

Question 4

What is the preferred collection container and preservative for a urine specimen tested for catecholamines (epinephrine, norepinephrine)?

Accepted Answer

Acidified collection jug (6N HCl preservative), kept cold

Answer

Catecholamines are unstable in alkaline or neutral pH; acidifying urine to pH <3 with HCl preserves them from oxidative degradation throughout the 24-hour collection.

Question 5

According to CLSI standards, what is the maximum recommended time between venipuncture and centrifugation for a serum tube?

Accepted Answer

30 minutes to 1 hour after complete clotting

Answer

CLSI recommends centrifugation within 30–60 minutes of collection after complete clot formation to minimize analyte degradation and cellular metabolism effects.

AACC - American Association for Clinical Chemistry Certification Practice Test

AACC - American Association for Clinical Chemistry Certification Practice Test

AACC AACC Specimen Collection & Processing 3