Phlebotomy Education
The Order of Draw and Why It Exists
Cross-contamination of additives produces results that look real and are entirely wrong.
11 May 2026 · 5 min read
The sequence
Blood cultures, then citrate, then serum, then heparin, then EDTA, then fluoride oxalate — protecting the most sensitive assays first.
What goes wrong
EDTA carryover falsely raises potassium and lowers calcium; heparin carryover distorts coagulation studies.
Habit over memory
Lay tubes out in order before you start. A physical routine beats recall under pressure.