Capillary and Venous Lactate Compared in ED Patients

Elevated lactate levels are a common finding in acutely unwell patients. Blood lactate level is a good predictor of patient outcome and high lactate levels are associated with high morbidity and mortality. Lactate may be detected and measured in all blood samples: arterial, venous and capillary.

Currently, blood lactate can be measured formally in the laboratory, using blood gas analyzers or with handheld devices. Strong correlations have been shown between blood lactate levels in samples analyzed in the central laboratory, by blood gas analyzers and handheld devices. Capillary blood lactate testing with handheld analyzers has great advantages to reduce the time needed for clinical decisions, and for extended use in the prehospital setting.

Emergency department (ED) personnel at the Chinese University of Hong Kong (Shatin, Hong Kong) and their colleagues carried out a prospective observational study of patients presenting to the ED of Prince of Wales Hospital (Shatin, Hong Kong) and 240 patients (mean age 69.9 years) were recruited. Venous and capillary blood samples were collected for lactate analysis. Venous blood samples (approximate 1 mL) were collected by venipuncture while capillary blood samples were collected by finger-prick with a disposable lancet.

Venous lactate levels were measured by blood gas analyzer the Siemens Automatic QC RAPID Systems RAPIDPoint 500 (VL-Ref) served as the reference standard. Capillary lactate levels were immediately analyzed by two handheld lactate analyzers: Nova StatStrip Xpress Lactate Meter (CL-Nova) and Lactate Scout+ (CL-Scout). Venous lactate levels were also measured on the two handheld lactate analyzers. All lactate measurements were performed within 15 minutes after obtaining the venous sample.

The scientists reported that the results of VL-Ref ranged from 0.70 to 5.38 mmol/L (mean of 1.96 mmol/L). Regarding capillary lactate measurements, the bias (mean difference) between VL-Ref and CL-Scout+ was −0.22 with 95% limits of agreement (LOA) of −2.17 to 1.73 mmol/L and the bias between VL-Ref and CL-Nova was 0.46, with LOA of −1.08 to 2.00 mmol/L. For venous lactate, results showed the bias between VL-Ref and VL-Scout+ were 0.22 with LOA being −0.46 to 0.90 mmol/L, and the bias between VL-Ref and VL-Nova was 0.83 mmol/L with LOA −0.01 to 1.66 mmol/L.

The author concluded that their study shows poor agreement between capillary lactate and reference values. The study does not support the clinical utility of capillary lactate point-of-care testing (POCT). However, venous lactate measured by Scout+ handheld analyzer may have potential for screening patients who may need further testing. The study was published on April 3, 2019, in the journal BMJ OPEN.

Related Links:
Chinese University of Hong Kong
Prince of Wales Hospital