Effect of different pre-analytical conditions on plasma lactate concentration.

INTRODUCTION: Plasma lactate is a frequently used and important parameter for medical decision making. To setup a pre-analytical algorithm, we aimed to investigate the influence of different test tube additives, aliquoting, ice storage and haemolysis on plasma lactate concentrations for possible sparing critically ill (ICU) patients of additional blood drawing. MATERIALS AND METHODS: In our study (N = 177), lactate concentration and haemolysis index (HI) were measured in aliquoted (AHP) and unaliquoted (HP) Li-heparin, NaF/K3EDTA and NaF/KOX plasma, centrifuged within 15 minutes after venipuncture, on Cobas c501 analyzer. Differences were tested using the Wilcoxon's test and Passing-Bablok regression. Clinical accuracy of results was assessed in 107 ICU patients based on reference interval and clinical decision limits. RESULTS: Lactate concentrations did not differ in NaF/K3EDTA and NaF/KOX plasma (P = 0.855). No clinically significant difference of AHP compared to NaF/K3EDTA lactate was found (y = 0.13 (0.08 to 0.19) + 1.02 (0.99 to 1.08) x) if samples were aliquoted within 30 minutes after venipuncture. On contrary, lactate concentrations in HP showed significant proportional difference (y = 0.07 (- 0.12 to 1.24) + 1.37 (1.22 to 1.56) x) and were clinically incorrect in 14% of patients. Transport in ice bath increases HI in NaF/K3EDTA (P < 0.001), but without influencing lactate results compared to room temperature (y = 0.03 (- 0.06 to 1.00) + 1.05 (0.99 to 1.11) x). CONCLUSIONS: Lactate determination in HP is unacceptable because of high proportional error and high risk of clinical inaccuracy compared to NaF/K3EDTA. If pre-analytical conditions are met, AHP, NaF/K3EDTA and NaF/KOX plasma can be used interchangeably. Aliquoted Li-heparin samples alow measurement of other biochemical tests from a single tube and can spare ICU patients from additional blood drawing. Storage in ice bath provides no additional stabilization in NaF/K3EDTA tubes.