Prehospital point-of-care lactate (pLA) measurement may be a useful tool to assist paramedics with diagnosing a range of conditions, but only if it can be shown to be a reliable surrogate for serum lactate (sLA) measurement. The aim of this study was to determine whether pLA is a reliable predictor of sLA.
This was a retrospective study of adult patients over a 12-month period who had pLA measured by paramedics in an urban Australian setting and were transported by ambulance to a tertiary hospital where sLA was measured. Patients were excluded if they suffered a cardiopulmonary arrest at any time, had missing data, or if sLA was not measured within 24 hours of arrival. Levels of agreement were determined using methods proposed by Bland and Altman.
A total of 290 patients were transported with a pLA recorded. After exclusions, there were 155 patients (55.0% male; age 71 [SD=18] years) remaining who had sLA recorded within 24 hours. Elevated pLA (>2.0mMol/L) was associated with sLA measurement (76.1% vs 23.9%; OR 3.18; 95% CI, 1.88-5.37; P<.0001). Median time between measurements was 89 minutes (IQR=75). Overall, median pLA was higher than sLA (3.0 [IQR=2.0] mMol/L vs 1.7 [IQR=1.3]; P<.001). Bland-Altman analysis on all participants showed a mean difference of 1.48 mMol/L (95% CI, -3.34 to 6.31). Normal pLA was found to be a true negative in 82.9% of cases, and elevated pLA was a true positive in 48.3% of cases. When the time between measurements was less than 60 minutes (n=25), normal pLA predicted normal sLA with 100% accuracy, with a false-positive rate of 18.2%. As time between measurements increased, accuracy diminished and the false-positive rate increased.
Overall, the level of agreement between pLA and sLA was poor. Accuracy of pLA diminished markedly as the time between the two measurements increased. It may be possible to use pLA as a screening tool; when considered this way, pLA performed much better, though larger prospective trials would be needed to confirm this.
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