Question 1

What is the correct order of draw for blood collection tubes?

Accepted Answer

The CLSI GP41 standard order of draw is: (1) blood culture bottles, (2) light blue (sodium citrate) for coagulation, (3) serum tubes — red (no additive or clot activator) and gold/SST (serum separator) at the same position, (4) green (heparin) for plasma chemistry, (5) lavender/purple (EDTA) for CBC and HbA1c, (6) gray (fluoride/oxalate) for glucose and lactate.

Question 2

Why does the order of draw matter in phlebotomy?

Accepted Answer

Trace additives carry over from the needle hub and tube stopper into the next tube drawn. Wrong draw order can cause EDTA from a lavender top to falsely lower calcium in a gold/SST tube, or heparin from a green top to prolong PT and PTT in a sodium citrate tube.

Question 3

What tube is used for a CBC (complete blood count)?

Accepted Answer

A lavender (purple) EDTA tube is used for a CBC and differential. It is the 5th step in the CLSI GP41 draw order and requires 8–10 gentle inversions.

Question 4

What tube is used for a lipid panel or metabolic panel (BMP/CMP)?

Accepted Answer

A gold top serum separator tube (SST) is used for routine chemistry including lipid panels, BMP, and CMP. It is the 3rd step in the CLSI GP41 draw order (same position as plain red tubes), requires 5–10 gentle inversions, and needs adequate clotting time before centrifugation — commonly 30 minutes for SST/gel tubes.

Question 5

What tube is used for PT/INR and coagulation studies?

Accepted Answer

A light blue sodium citrate tube is used for PT/INR, PTT, fibrinogen, D-dimer, and coagulation assays. It is the 2nd step in the CLSI GP41 draw order, must be filled to the line to maintain the 9:1 blood-to-citrate ratio, and requires 3–5 gentle inversions.

Question 6

What tube is used for a glucose test or glucose tolerance test (GTT)?

Accepted Answer

A gray top fluoride/oxalate tube is used for fasting glucose, GTT, and lactate. It is drawn last (6th step) because potassium oxalate/sodium fluoride carryover can severely interfere with potassium, calcium, and enzymatic chemistry panels if drawn earlier. It requires 8–10 gentle inversions.

Question 7

What tube is used for HbA1c?

Accepted Answer

A lavender (purple) EDTA tube is used for HbA1c (glycated hemoglobin). It requires 8–10 gentle inversions and is the 5th step in the CLSI GP41 draw order.

#	Tube	Additive	Inversions	Common uses
1	Yellow / SPS Blood culture bottles	Sodium polyanethol sulfonate (SPS) or culture media Collect aerobic bottle first, then anaerobic. Fill to the line marked on the bottle.	8–10× gentle	Aerobic bacterial cultures Anaerobic bacterial cultures Fungal cultures
2	Light blue Sodium citrate (coagulation)	3.2% sodium citrate (9:1 blood-to-additive ratio required) Fill to the line exactly — underfill alters the 9:1 ratio and invalidates results.	3–5 gentle× gentle	PT / INR PTT Fibrinogen D-dimer Coagulation factor assays
3	Red & Gold / SST Serum tubes (same draw position per CLSI GP41)	Clot activators, gel separators, or none (glass) (0× for rare glass plain red tubes; 5× for plastic clot-activator red tubes; 5–10× for gold SST) Allow adequate clot time before centrifuging — commonly 30 minutes for SST/gel tubes; plain red tubes without additive may require longer. Follow manufacturer labeling.	5–10 gentle× gentle	Routine serum chemistry (BMP, CMP) Thyroid / hormones Select drug levels Serology / send-out tests
4	Green Sodium or lithium heparin	Sodium heparin or lithium heparin (anticoagulant)	8–10× gentle	Stat plasma chemistry Ammonia Chromosome analysis (sodium heparin) HLA typing
5	Lavender / purple EDTA	Ethylenediaminetetraacetic acid (EDTA) — chelates calcium	8–10× gentle	CBC / differential HbA1c Blood bank compatibility testing Reticulocyte count
6	Gray Fluoride / oxalate	Potassium oxalate + sodium fluoride (glycolysis inhibitor) Draw last — potassium oxalate/sodium fluoride carryover can severely interfere with potassium, calcium, and enzymatic chemistry panels if drawn earlier.	8–10× gentle	Fasting glucose Glucose tolerance test (GTT) Lactate

Order of draw

Why does draw order matter?

Which tube is used for each blood test?