Preanalytical handling of samples for measurement of plasma lactate in HIV patients

Abstract

Lactic acidosis is a feared side effect of nucleoside analog treatment, one of the cornerstones in the management of HIV infection. Precise and reliable lactate measurements are prerequisites for the diagnosis of hyperlactatemia. The effects of venous stasis, time to measurement and storage temperature on p‐lactate levels, p‐glucose levels, anion gap and pH were investigated. Ten HIV patients (n=8 on highly active antiretroviral therapy) and 4 healthy control subjects were studied. Blood was drawn without stasis at time 0 and with stasis for 2 and 8 min into heparin‐preserved test tubes. The tubes were placed at a room temperature (25°C) and on crushed ice and consecutively monitored for up to 360 min. The mean increases in p‐lactate in blood kept in test tubes at 25°C, measured from 0 to 60 min and from 240 to 360 min, were increased in HIV patients compared with controls (0.78 mmol/Lh±0.02 vs. 0.63 mmol/Lh±0.05, (p=0.009) and 0.65 mmol/Lh±0.03 vs. 0.53 mmol/Lh±0.05, (p=0.042)). It was found that placing the tubes on crushed ice rather than keeping them at 25°C controlled glycolysis and lactate production measured over a 6‐h period (0.033 mmol/Lh±0.006 vs. 0.32 mmol/Lh±0.01, (p<0.0001) and 0.064 mmol/Lh±0.008 vs. 0.64 mmol/Lh±0.02, (p<0.0001)). The total increases in lactate levels in the test tubes placed on crushed ice for 4 h and in those kept at 25°C for 15 min were comparable (0.28±0.03 mmol/L vs. 0.20±0.03). Compared with storage at 25°C, keeping the test tubes on crushed ice also preserved pH and anion gap over a 6‐h measurement period (pH: 0.026±0.004 vs. 0.12±0.01 and anion gap: −0.8±0.4 mmol/L vs. 4.1±0.4). Two minutes of venous stasis had no influence on p‐lactate levels (0.02±0.04 mmol/L, p=0.70), whereas 8 min of stasis increased p‐lactate levels by 0.11±0.04 mmol/L, p=0.009. It is concluded that major errors in measurements of p‐lactate, anion gap and pH can be prevented by placing test tubes on crushed ice for up to 4 h until measurement.

• Anion gap
• lactate
• lactic acidosis
• NRTI
• pH
• preanalytical variation