Laboratory Testing & Procedures Flashcards

A single control value falls outside the mean ±3 SD. Which Westgard rule is violated, and what action is required?

Answer: 1-3s; reject the run and investigate

The 1-3s rule detects random error, so the run must be rejected and the problem investigated.

Which analyte is most falsely increased by in vitro hemolysis?

Answer: Potassium

RBCs contain much more potassium than plasma, so lysed cells release it and falsely raise results.

What is the required blood-to-anticoagulant ratio in a light blue top tube used for coagulation testing?

Answer: 9:1

Sodium citrate coagulation tubes must be filled to a 9:1 blood-to-citrate ratio for accurate results.

According to CLSI order of draw, which tube should be collected FIRST?

Answer: Blood culture bottles

Sterile blood culture specimens come first to prevent contamination.

Why is a gray top tube containing sodium fluoride preferred for glucose testing when processing is delayed?

Answer: It inhibits glycolysis

Fluoride inhibits enolase, stopping cells from consuming glucose in the tube.

A grossly lipemic specimen interferes with a spectrophotometric assay. What is the best way to remove the interference?

Answer: Ultracentrifugation

Ultracentrifugation separates the lipid layer so the cleared infranatant can be tested.

A patient with a hematocrit of 62% needs a PT/aPTT. What adjustment should be made to the collection tube?

Answer: Decrease the volume of citrate

High hematocrit means less plasma, so citrate must be reduced to keep the correct plasma-to-anticoagulant ratio.