CPHT Order of Draw & Tube Additives 3

Question 1

How many times should a lavender (EDTA) tube be gently inverted immediately after blood collection?

Accepted Answer

8-10 inversions

Answer

EDTA tubes require 8-10 gentle inversions to ensure complete mixing of blood with the anticoagulant, preventing microclot formation that would invalidate a CBC or differential.

Question 2

A sodium citrate tube must be filled to what level for coagulation results to be considered valid?

Accepted Answer

Within ±10% of the required fill volume

Answer

Citrate tubes must be filled to within ±10% of their required volume to maintain the critical 9:1 blood-to-sodium-citrate ratio needed for accurate PT/INR and aPTT results.

Question 3

If EDTA carryover from a lavender tube occurs into a serum chemistry tube, which electrolyte result is most likely to be falsely elevated?

Accepted Answer

Potassium (K+)

Answer

Dipotassium EDTA carryover into chemistry tubes can cause falsely elevated potassium levels, potentially triggering unnecessary clinical interventions for pseudo-hyperkalemia.

Question 4

A phlebotomist accidentally draws an SST (gold) tube before the light blue (citrate) tube. What is the correct corrective action?

Accepted Answer

Draw a discard tube to flush residual clot activator before collecting the citrate tube

Answer

Drawing a discard tube after the SST flushes clot activator particles from the needle, preventing them from entering the citrate tube and falsely shortening coagulation clotting times.

Question 5

For which analyte is a plain red top tube (no gel separator) preferred over a gold SST tube?

Accepted Answer

Serum iron testing

Answer

Plain red top tubes are preferred for serum iron testing because the polyester gel in SST tubes can adsorb iron, leading to falsely decreased serum iron concentration results.

CPHT - Certified Phlebotomist Practice Test

CPHT - Certified Phlebotomist Practice Test

CPHT Order of Draw & Tube Additives 3