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Section 2 of 6 · Open sections

Required section · Section 2 of 6

Why an order of draw exists at all

The order of draw exists to control additive carryover, not to match tube colors. A trace amount of blood, and whatever additive it carries, can travel forward into the next tube through the needle, the tubing, or the collection device hub. If that carryover additive is incompatible with the next tube's test, the next result is compromised before it is ever analyzed.

The current CLSI (Clinical and Laboratory Standards Institute) sequence is blood culture or sterile collection first, then citrate, then serum, then heparin, then EDTA (ethylenediaminetetraacetic acid), then a fluoride or oxalate glycolytic inhibitor tube last. This order holds whether the collection uses a syringe, a tube holder, or a preevacuated tube system; the device changes, the additive logic does not.

The clearest failure mode is a serum tube's clot activator carrying into a citrate coagulation tube ahead of it. Clot activator promotes clotting, and even a trace amount reaching a citrate tube can alter the plasma-based coagulation result that tube is meant to produce. This is why serum is sequenced after citrate rather than before it.

Not every additive in a laboratory's tube inventory appears in the core sequence above. When a tube carries an additive that is not explicitly listed, it is placed by reasoning through how that additive could alter whatever specimen is drawn immediately after it, not by matching it to a cap color chart.

Think in additive classes, not in cap colors, and you can reason through a device or vendor change without relearning the whole sequence.

Illustrative drawing — this picture was drawn rather than captured.

Diagram of six additive-class boxes in sequence: blood culture, citrate, serum, heparin, EDTA, and fluoride or oxalate, with a coral warning box showing a clot activator carrying into a citrate tube if serum is drawn out of order.
Figure 1The current CLSI order of draw and the clot-activator carryover it prevents

Current venous order of draw by additive class

  1. Blood culture or sterile collection

    Drawn first, before any additive tube, to keep the culture bottle free of additive contamination and to protect sterility.

  2. Citrate (coagulation)

    Drawn next and filled to the manufacturer's line so the blood-to-citrate ratio that plasma-based coagulation testing depends on is preserved.

  3. Serum, including clot activator

    Follows citrate. Its clot activator must never reach a citrate tube ahead of it, which is why serum is sequenced after coagulation collection.

  4. Heparin

    Plasma chemistry collection follows serum in the additive sequence.

  5. EDTA

    Whole blood collection for complete blood count and differential follows heparin.

  6. Fluoride or oxalate glycolytic inhibitor

    Drawn last in the core sequence; the glycolytic inhibitor protects glucose stability and does not need to precede the other additive classes.

Knowledge checks

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Knowledge check 1

Why does the current order of draw place serum tubes after citrate tubes?

Choose one option.

Knowledge check 2

A collector switches from a preevacuated tube system to a syringe draw for a difficult stick. What happens to the order of draw?

Choose one option.

Knowledge check 3

An unfamiliar additive tube with an additive that is not explicitly named in the core CLSI sequence needs to be placed. What is the correct approach?

Choose one option.

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