AACC AACC Specimen Collection & Processing

Question 1

Which tube additive is found in a lavender/purple-top tube used for hematology testing, and what is its mechanism of action?

Accepted Answer

EDTA — chelates calcium and magnesium to inhibit coagulation

Answer

EDTA (ethylenediaminetetraacetic acid) in lavender-top tubes chelates divalent cations required for the coagulation cascade, preserving cell morphology for CBC analysis.

Question 2

What is the recommended order of draw when collecting multiple tubes by venipuncture, according to CLSI guidelines?

Accepted Answer

Blood cultures → light blue → red/SST → green → lavender → gray

Answer

The CLSI-recommended order of draw minimizes additive carryover: blood cultures first (sterility), then light blue (citrate), red/SST, green (heparin), lavender (EDTA), and gray (fluoride/oxalate).

Question 3

What is the maximum acceptable time for a serum specimen to remain as a clot before centrifugation under standard pre-analytical conditions?

Accepted Answer

15–30 minutes at room temperature

Answer

Serum tubes should be allowed to clot for 15–30 minutes at room temperature before centrifugation to ensure complete fibrin formation and prevent fibrin strands in the serum.

Question 4

Which pre-analytical variable is most likely to cause falsely elevated serum potassium levels?

Accepted Answer

Hemolysis releasing intracellular potassium into the sample

Answer

Hemolysis releases potassium from erythrocytes into the serum, causing falsely elevated results because intracellular potassium concentration is approximately 20–30 times higher than plasma levels.

Question 5

For glucose testing, why is a gray-top tube (sodium fluoride/potassium oxalate) preferred over a serum tube?

Accepted Answer

Sodium fluoride inhibits glycolysis, preserving glucose concentration

Answer

Sodium fluoride inhibits enolase, a glycolytic enzyme, halting glucose metabolism by red blood cells and stabilizing glucose levels for up to 24 hours.

AACC - American Association for Clinical Chemistry Certification Practice Test

AACC - American Association for Clinical Chemistry Certification Practice Test

AACC AACC Specimen Collection & Processing