Haemolysis: causes and how to prevent specimen rejection

Some complications of venepuncture are visible at the bedside. Haemolysis is not — it shows up only when the laboratory rejects the sample or returns an uninterpretable result. It is the most common cause of specimen rejection, and almost every cause is preventable with good technique.

What haemolysis is

Haemolysis is the destruction of red blood cells in the collected sample. When red cells rupture, their contents — most importantly potassium — leak into the surrounding plasma or serum, which can make a result clinically misleading or unusable. Each rejection means a repeat draw, a delay to the patient's care, and a re-cost to the service.

What causes it

Most haemolysis is mechanical: the red cells are damaged by force or friction somewhere between the vein and the tube.

A needle that is too small for the vein — a gauge of 23 or finer for a routine draw — shears cells as they pass through the narrow bore.
Forceful aspiration, or pushing blood through the needle when transferring from a syringe.
Vigorous mixing or shaking instead of gentle inversion.
A prolonged tourniquet time, which also drives haemoconcentration.
Drawing from an existing IV line, or puncturing before the alcohol antiseptic has dried.
Delayed processing or transport at the wrong temperature.

Use a 21–22 gauge needle for routine adult draws.
Let the vacuum or a gentle plunger pull draw the blood naturally.
Mix additive tubes by gentle inversion, five to ten times.
Allow the alcohol antiseptic 30 seconds to dry before puncture.

Don't

Use a needle gauge that is too small (23 or finer) for a routine draw.
Force blood through the needle or pull the plunger hard.
Shake the tubes — shaking is what haemolyses the sample.
Draw from an IV site or puncture before the antiseptic has dried.

Why gentle inversion, not shaking

Additive tubes need mixing so the additive reaches all of the blood — but the mixing has to be gentle. An inversion is a full top-to-bottom rotation and back, repeated the manufacturer-specified number of times. Shaking generates the mechanical force that ruptures red cells, so the act meant to preserve the sample becomes the act that ruins it.

This guide is a free extract from PhlebMastery's WHO-based phlebotomy theory course. The full treatment — every common complication, from haematoma to nerve injury, and how to recover a difficult draw — is in Module 9: Complications & Troubleshooting. New here? Start with the free Module 1, or see the whole course — full access is a one-time purchase.