CMT Specimen Collection and Pre-Analytical Processing

Question 1

Following the CLSI order of draw, which tube is collected first among these?

Accepted Answer

Light blue (sodium citrate)

Answer

The CLSI order is blood cultures, light blue citrate, serum tubes (red/gold), green heparin, lavender EDTA, then gray fluoride/oxalate. Citrate goes before the other additive tubes so carryover doesn't affect coagulation testing.

Question 2

What blood-to-anticoagulant ratio is required in a light blue sodium citrate tube for coagulation testing?

Accepted Answer

9:1

Answer

Coagulation tubes need a 9:1 ratio of blood to 3.2% sodium citrate. Underfilling leaves extra citrate, which falsely prolongs the PT and aPTT.

Question 3

Why is a gray-top tube with sodium fluoride preferred for glucose testing when processing will be delayed?

Accepted Answer

It inhibits glycolysis

Answer

Sodium fluoride inhibits enolase and so blocks glycolysis by blood cells. This keeps glucose stable; without it, glucose falls by about 5–7% per hour at room temperature.

Question 4

A hemolyzed specimen is most likely to falsely raise which analyte?

Accepted Answer

Potassium

Answer

Red cells hold far more potassium than plasma does. Hemolysis releases that intracellular potassium and falsely raises the result. LD, AST, and magnesium are affected in the same way.

Question 5

How should a blood specimen for plasma ammonia be handled?

Accepted Answer

Placed on ice and analyzed promptly

Answer

Ammonia keeps rising in vitro because of cellular metabolism and deamination of amino acids. The specimen should go on ice, be separated quickly, and be tested promptly.

CMT - Certified Medical Technologist Practice Test

CMT - Certified Medical Technologist Practice Test

CMT Specimen Collection and Pre-Analytical Processing