Lactate measurement – point of care versus the laboratory

Lactate measurement is important for diagnostic and prognostic assessment of the critically ill. Traditionally, lactate has been measured on serum/plasma samples in the central laboratory, but modern blood gas and other point-of-care analyzers now provide the means for real-time monitoring of lactate on whole blood at the patient’s bedside. 

Although these newer methods have been well validated, it remains unclear if results obtained at the point of care are interchangeable with those obtained in the central laboratory. This is the issue addressed by a recently published study in which lactate results obtained by three whole-blood point-of-care methodologies (two blood gas analyzers and one dedicated lactate analyzer) were compared with those obtained using two laboratory-based plasma assays. 

A single anticoagulated blood sample from each of 90 intensive care patients was submitted for lactate measurement using the three different point-of-care analyzers. All analyses were complete within an hour of blood sampling. Immediately (within 5 minutes) after analysis, blood samples were centrifuged and the recovered plasma submitted for lactate analysis using the two laboratory-based methods. 

For statistical analysis of results by the five methods, one of the laboratory-based plasma methods was chosen as the reference methodology. All three point-of-care methods, as well as the other plasma laboratory-based assay, showed good correlation (correlation coefficients r² all 0.99 or greater) when compared with this chosen reference method. 

Bland-Altman plots revealed very close agreement between the two plasma methods across the full concentration range (1-14 mmol/L) of the 90 specimens. Compared with all other methods, the dedicated point-of-care lactate analyzer reported slightly higher lactate results across the concentration range. 

Both point-of-care blood gas analyzer methods showed excellent agreement with laboratory-based methods across the concentration range of 0.8-6.0 mmol/L (i.e. normal and moderately raised lactate) but slightly lower results (compared with laboratory-based methods) above a lactate concentration of 6.0 mmol/L. 

The results of this study suggest that laboratory and point-of-care blood gas analyzer lactate results are interchangeable so long as the lactate concentration is less then 6.0 mmol/L. For those with the most severe increase (lactate >6.0 mmol/L), it is important that either point-of-care or laboratory-based methods be used for monitoring.