Specimen Collection and Pre-Analytical Processing Flashcards

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

Answer: Light blue (sodium citrate)

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.

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

Answer: 9:1

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.

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

Answer: It inhibits glycolysis

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.

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

Answer: Potassium

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.

How should a blood specimen for plasma ammonia be handled?

Answer: Placed on ice and analyzed promptly

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.

Leaving a tourniquet on for more than 1 minute during venipuncture can cause which of the following?

Answer: Hemoconcentration and falsely high protein and cell counts

Prolonged venous stasis pushes fluid out of the vessel into the tissues. Large molecules and cells become concentrated, which falsely raises protein, cholesterol, calcium, and cell counts.