Factors affecting blood sample haemolysis: a cross-sectional study.

OBJECTIVE

To determine the effect of blood sampling through an intravenous catheter compared with a needle in Emergency Department blood sampling.

METHODS

We undertook a prospective, cross-sectional study in a UK university teaching hospital Emergency Department. A convenience sample of 985 patients who required blood sampling via venepuncture was collected. A total of 844 complete sets of data were analysed. The median age was 63 years, and 57% of patients were male. The primary outcome measure was the incidence of haemolysis in blood samples obtained via a needle compared with samples obtained via an intravenous catheter. Secondary outcome measures defined the effect on sample haemolysis of the side of the patient the sample was obtained from, the anatomical location of sampling, the perceived difficulty in obtaining the sample, the order of sample tubes collected, estimated tourniquet time and bench time. Data were analysed with logistic regression, and expressed as odds ratios (95% confidence intervals; P-values).

RESULTS

Blood samples obtained through an intravenous catheter were more likely to be haemolysed than those obtained via a needle, odds ratio 5.63 (95% confidence interval 2.49-12.73; P<0.001).

CONCLUSION

Blood sampling via an intravenous catheter was significantly associated with an increase in the likelihood of sample haemolysis compared with sampling with a needle. Wherever practicable, blood samples should be obtained via a needle in preference to an intravenous catheter. Future research should include both an economic evaluation, and staff and patient satisfaction of separating blood sampling and intravenous catheter placement.