Effects of time, temperature and blood cell counts on levels of lactate in heparinized whole blood gas samples

Abstract

Objective: To investigate whether lactate levels may vary in relation to time, substrate concentration and blood cells counts. Methods: In this study 110 samples from the daily clinical routine blood samples were collected. Determinations of lactate were made at different times where the samples had not been left for more than 120 min at room temperature (24°C) or in the fridge (4°C). The influence of glucose and blood cells on lactate production was also estimated. The rate in change of concentration (slope) and the increase expected at the beginning (intercept) were estimated through linear regression using a longitudinal marginal method. Results: The time‐related change in lactate was significantly higher at room temperature (0.012 mmol L⁻¹ min⁻¹) than at 4°C (0.0035 mmol L⁻¹ min⁻¹) (p<0.0001). There was a significantly positive relationship between blood cells (mainly leucocytes) and the rate of reaction at room temperature. Conclusions: A delay in the processing of a whole blood sample of more than 15 min at room temperature or an hour in the fridge entails an important overestimation of the initial lactate levels. Pronounced leucocytosis (higher than 6×10¹⁰/L) meaningfully cut down the stability period (10 min).