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Clinic sourcing guide

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Blood Collection Tube Cap Colors Explained (2026 Guide)

What each blood tube cap color means, its additive and which tests it is used for — a practical 2026 reference for clinics and laboratories.

Blood collection tubes are color-coded by the additive inside them. The cap color tells the phlebotomist and the lab which additive the tube contains and, therefore, which tests it is suitable for. Using the wrong tube can invalidate a sample, so the color system is a global safety convention (broadly aligned with ISO 6710).

Common cap colors and their additives

  • Red — no additive (or clot activator in plastic tubes). Serum tests, serology, biochemistry.
  • Yellow (gold / SST) — clot activator + separator gel. Serum biochemistry and hormone panels.
  • Light blue — sodium citrate (3.2%). Coagulation tests (PT, aPTT, INR). Must be filled to the line.
  • Lavender / purple — EDTA. Whole-blood hematology (CBC), HbA1c, blood group.
  • Green — heparin (lithium/sodium). Plasma chemistry, some STAT tests.
  • Grey — sodium fluoride / potassium oxalate. Glucose and lactate (inhibits glycolysis).

Order of draw

When multiple tubes are drawn, the order of draw prevents additive carryover: blood culture → light blue (citrate) → serum (red/gold) → green (heparin) → lavender (EDTA) → grey (fluoride). Always follow your laboratory's validated protocol.

PRP tubes

PRP/PRF tubes are a separate category selected by protocol, volume and cap/additive type rather than by the routine phlebotomy color scheme. Match the tube to your centrifuge and clinical protocol.

This article is a general reference and not a substitute for your laboratory's validated procedures.