Specimen rejection: why blood samples get rejected and how to prevent it

A sample can be drawn perfectly and still be useless. Specimen rejection is the laboratory's refusal to run a sample that cannot give a safe result — and every rejection means a repeat draw, a delay to the patient's care, and a re-cost to the service. A well-run service keeps its rejection rate under 2%. Almost every rejection traces back to something that happened in the phlebotomist's hands, which means almost every rejection is preventable. These are the reasons a sample gets rejected, and the practice that prevents each.

Haemolysis — the most common reason

Haemolysis is the destruction of red blood cells in the sample, and it is the single most common pre-analytical error. The damaged cells leak potassium and other contents into the sample, so the laboratory cannot trust the result.

Most haemolysis is mechanical and avoidable: a needle too small for the vein, blood forced through the needle, vigorous shaking instead of gentle mixing, a tourniquet left on too long, drawing through an IV line, or delayed processing. Let the vacuum draw the blood at its own pace, and mix additive tubes by gentle inversion — never by shaking.

Clotting and underfilled tubes

An additive tube that is not mixed promptly, or is filled too slowly, can clot — and a clotted haematology or coagulation sample is rejected. Invert each additive tube the manufacturer-specified number of times immediately after the draw, and keep the blood flowing during collection.

Insufficient sample volume is the mirror problem. Additive tubes depend on a fixed blood-to-additive ratio: a sodium citrate coagulation tube must be filled to the line, because its 1:9 citrate-to-blood ratio is wrong if it is under-filled, and the laboratory will reject it. Underfilling usually comes from a collapsed vein, a lost-vacuum tube, or a needle not quite in the vein.

Mislabelling — the rejection that risks real harm

A perfectly drawn sample with the wrong name on it is, clinically, the wrong sample. Mislabelling is a leading cause of rejection and the one with the most serious consequences, because a mislabelled tube that is not caught can send one patient's result to another patient's chart.

The two predictable failures are pre-labelling empty tubes and labelling away from the patient. The fix is bedside labelling: label each tube at the patient's side, immediately after collection and before you leave, then check the label against the request form. The target for labelling errors is zero.

Wrong tube, contamination, and delay

The remaining rejections come from a short list:

• Wrong tube for the test. Verify the test requirements and use the right additive — drawing the wrong colour gives a result that looks precise but is clinically meaningless. Drawing tubes in the correct order of draw also prevents additive carryover between them.
• Contamination. Poor skin preparation or touching the cleaned site after antisepsis can contaminate the sample — most critically for blood cultures, where the contamination target is under 3%.
• Delayed transport. Many analytes change with time off the patient; some tests must reach the laboratory within 30 to 60 minutes. A correctly drawn sample that arrives too late is still a rejection.

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This guide is a free extract from PhlebMastery's phlebotomy theory course, with content aligned to published WHO guidance. The full treatment — labelling, mixing, storage, transport, and the quality-assurance framework around them — is in Module 8: Quality Assurance & Specimen Handling. New here? Start with the free Module 1, or see the whole course — full access is a one-time purchase.