CMLA Specimen Collection & Processing

Question 1

What is the correct order of draw when collecting multiple blood tubes using a vacutainer system?

Accepted Answer

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

Answer

The CLSI-recommended order of draw begins with blood cultures (sterile), followed by light blue (coagulation), then serum tubes, heparin, EDTA, and finally fluoride/oxalate to prevent additive carryover between tubes.

Question 2

Which evacuated tube color is used for coagulation studies such as PT and aPTT?

Accepted Answer

Light blue (sodium citrate)

Answer

Light blue tubes contain sodium citrate, which binds calcium and prevents clotting; the 9:1 blood-to-anticoagulant ratio is critical for accurate coagulation assays like PT and aPTT.

Question 3

At what angle should the needle be inserted when performing a standard venipuncture?

Accepted Answer

15–30 degrees

Answer

A 15–30 degree angle (bevel up) allows the needle to enter the vein smoothly without passing through the posterior wall, minimizing trauma and hematoma formation.

Question 4

How long should a tourniquet remain applied during blood collection to prevent hemoconcentration?

Accepted Answer

No more than 1 minute

Answer

A tourniquet left on for more than 1 minute causes hemoconcentration and may affect results for potassium, proteins, and other analytes by restricting blood flow.

Question 5

Which additive is found in lavender (purple) top tubes and is used for most hematology testing?

Accepted Answer

EDTA (ethylenediaminetetraacetic acid)

Answer

EDTA chelates calcium ions to prevent coagulation and preserves cell morphology, making lavender tubes the standard choice for CBC and differential count.

CMLA - Certified Lab Assistant Practice Test

CMLA - Certified Lab Assistant Practice Test

CMLA Specimen Collection & Processing