Early vs. Late Tourniquet Release and Phlebotomy-Induced Hemolysis in the Emergency Department: TOURNI-ED

Plain-language summary

BACKGROUND: Hemolysis is the most common preanalytical error in emergency department (ED) laboratories, affecting 17-26% of blood samples collected in the ED and leading to test cancellations, repeat venipuncture, delayed diagnoses, and increased healthcare costs. Venous stasis created by tourniquet application during phlebotomy is a recognized contributing factor to hemolysis. While clinical guidelines recommend releasing the tourniquet once blood flow is established, the optimal timing of tourniquet release in relation to tube filling sequence has not been systematically evaluated. OBJECTIVE: The primary objective of this trial is to determine whether early release of sphygmomanometer-applied venous stasis (released after the first tube fills) reduces hemolysis rates compared to late release (released after the last tube fills) during routine phlebotomy in ED patients triaged as green or yellow category. DESIGN: Single-center, parallel-group, superiority randomized controlled trial with 1:1 allocation ratio. The trial was prospectively registered prior to the enrollment of the first participant. PARTICIPANTS: Adult patients (≥18 years) presenting to the emergency department with triage category green (semi-urgent) or yellow (urgent), for whom blood collection is indicated as part of routine clinical care. Patients requiring blood collection from an intravenous catheter, those with known coagulation disorders, and those who decline to participate are excluded. INTERVENTIONS: Group A (Early Release): Sphygmomanometer inflated to 60 mmHg for venous stasis; tourniquet released immediately after the first tube (sodium citrate, blue cap) completes filling. Remaining tubes (SST/gel, yellow cap; K2-EDTA, purple cap) are collected after release. Group B (Late Release): Sphygmomanometer inflated to 60 mmHg; tourniquet maintained throughout all tube filling and released only after the last tube (K2-EDTA, purple cap) completes filling. Tube collection order follows the CLSI H03-A6 standard for both groups. PRIMARY OUTCOME: Hemolysis rate, defined as the proportion of serum separator tube (SST/yellow cap) samples with a Hemolysis Index (HI) ≥ 1+ (corresponding to free hemoglobin ≥50 mg/dL), is assessed by the clinical chemistry laboratory analyzer. The outcome assessor (laboratory technician) is blinded to group assignment. SECONDARY OUTCOMES: (1) Distribution of ordinal hemolysis index categories (-, 1+, 2+, 3+, 4+, 5+) in SST samples; (2) Proportion of hemolyzed samples requiring repeat blood collection; (3) Total blood collection duration (seconds) from sphygmomanometer inflation to last tube filling completion; (4) Complication rate (hematoma, nerve injury, vasovagal reaction, arterial puncture, multiple puncture attempts). SAMPLE SIZE: A total of 792 participants (396 per group) are required based on an assumed hemolysis rate of 12% in the late release group and 6% in the early release group (50% relative risk reduction), α=0.05 (two-tailed), 80% power (Fleiss with pooled variance), plus 10% dropout buffer. RANDOMIZATION: Simple randomization using a computer-generated random number list (randomizer.org). The allocation sequence is maintained by a designated person not involved in enrollment or data collection. Allocation is revealed sequentially at the point of care. STATISTICAL ANALYSIS: Primary analysis: Chi-square test comparing hemolysis rates between groups (intention-to-treat population). Secondary analyses: Mann-Whitney U test for ordinal HI distribution; logistic regression for adjusted odds ratio. Bonferroni correction applied to multiple secondary comparisons (adjusted α = 0.017). Per-protocol analysis performed as a sensitivity analysis. Missing data handled using complete case analysis with sensitivity analysis.

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