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

Sodium citrate — chelates calcium to prevent clotting

Answer

Sodium fluoride — inhibits glycolysis

Answer

Lithium heparin — neutralizes thrombin activity

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

Lavender → light blue → red → green

Answer

Red → green → lavender → light blue → gray

Answer

Gray → lavender → green → red → light blue

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

5 minutes

Answer

2 hours refrigerated

Answer

4 hours at any temperature

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

Excessive tourniquet time causing hemoconcentration

Answer

Refrigerating the sample before centrifugation

Answer

Using a light blue-top tube instead of a red-top tube

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

It prevents lipemia from interfering with the glucose assay

Answer

It contains a gel barrier that separates glucose from cells faster

Answer

It prevents hemolysis that would falsely lower glucose

Question 6

When collecting a urine specimen for culture and sensitivity, which collection method is preferred to minimize contamination?

Accepted Answer

Midstream clean-catch in a sterile container

Answer

First-void morning specimen in a regular container

Answer

24-hour urine collected in a preservative jug

Answer

Catheterized specimen from the urinary bag port