Releasing the tourniquet as the first tube fills cut haemolysed emergency samples by a third

Design

Single-centre, parallel-group, randomised trial with blinded outcome assessment

Population

790 adult emergency patients, ESI 3–5, direct 21-gauge venepuncture

Primary outcome

Haemolysis index ≥1+ in serum separator tubes

Effect

17.2% vs 26.1%; absolute reduction 8.9 points (3.1–14.5); NNT about 11

Haemolysis is the commonest pre-analytical error in emergency samples. It falsely raises potassium and other analytes, delays decisions and forces repeat sampling. TOURNI-ED, a single-centre randomised trial published on 17 October, enrolled 792 adults triaged as Emergency Severity Index 3–5. Blood was drawn by direct 21-gauge venepuncture with stasis from a sphygmomanometer cuff at 60 mm Hg.

In one group, cuff deflation began as blood entered the first tube and finished as that tube filled. In the other, the cuff stayed up until the last tube filled. Haemolysis, judged by staff blinded to allocation, occurred in 17.2% with early release and 26.1% with late release: an absolute reduction of 8.9 percentage points (95% CI 3.1–14.5), or one haemolysed sample prevented for about every 11 patients. No early-release patient had stasis beyond 60 seconds, against 29% with late release. Failed or complicated draws were 8.1% against 5.6%, an imprecise difference that cannot be excluded.

The result applies to stable patients, direct venepuncture and a calibrated cuff. It does not cover blood drawn through cannulas, butterfly needles, elastic tourniquets or resuscitation patients. Within those limits, it is a free change in technique.

• Begin releasing the tourniquet as blood enters the first tube, and finish as that tube fills.
• Keep total tourniquet time under about one minute.
• Avoid drawing laboratory samples through a freshly placed cannula when a direct venepuncture is feasible.
• Treat an unexpectedly high potassium in a haemolysed sample as a reason to repeat, not to treat, unless the ECG or clinical picture suggests true hyperkalaemia.
• Watch for a small rise in failed draws when staff first change technique.

Why it matters

A no-cost change in technique prevented about one haemolysed sample for every 11 patients, saving repeat draws and false potassium alarms.

Don't overread it

One centre, stable patients, direct venepuncture and calibrated cuffs: the result may not transfer to cannula draws or elastic tourniquets.

The statistics, in plain English

A number needed to treat of about 11 means changing technique for 11 patients prevents one haemolysed sample. The complication difference (+2.5 points) has an interval from −1.0 to +6.1, so a small increase in failed draws is possible but unproven.

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