SIMULTANEOUS ANALYSIS OF PLASMA LACTATE AND PYRUVATE IN WHOLE BLOOD USING A UV/VISIBLE SPECTROPHOTOMETER; APPLICATION IN HYPOVOLEMIC SHOCK AND HYPOXIA

Abstract

Background: Unavailability of pyruvate quantification at the majority of the National Health Laboratory Service (NHLS) laboratories in South Africa prevents patient’s access to a lactate-to-pyruvate ratio (L:P ratio) determination. Thus the diagnosis and prognosis of hypoxemic conditions can be compromised. To obtain the ratio, lactate is measured; either using heparinised blood with a blood gas analyser as a point of care test (POCT) or in a sodium fluoride (NaF)/ potassium oxalate plasma on an automated laboratory analyser. Measurement of pyruvate concentrations in serum are offered at certain referral laboratories using a manual method and requires pre-packedclot enhanced serum tube (red top) with perchloric acid (PCA). The use of two different types of samples and additional sample preparation for L:P ratio is inconvenient for the patient, clinicians and alsoposes a risk for pre-analytical errors. This study aimed to determine if two tests can be consolidated in one NaF plasma tube whilst maintaining the perchlorate de-proteinisation to preserve pyruvate. Objectives: To compare pyruvate concentrations in the serum and plasma (anticoagulant: NaF) samples using a UV/visible spectrophotometer to assess the validity of using plasma for pyruvate analysis. Methods: Fifty patients with high whole blood lactate concentrations using a point of care analyzer at the Intensive Care Unit (ICU) were included in the study. Twenty-five specimens from a health control group were also included. Pyruvate was measured in perchloric acid treated serum and plasma samples using a UV/Visible spectrophotometer. The results of both types of samples were compared in both patient and control groups. Results: In the patient group, a correlation coefficient of R 2 between plasma and serum pyruvate results was 0.35 while in the control group was 0.36 demonstrating poor correlation. The mean of the serum pyruvate concentrations in the patient group was 0.151 mmol/L, and in the plasma samples was 0.065 mmol/L with P=0.00. The mean pyruvate concentration in the serum samples of the control group was 0.108 mmol/L and in the plasma samples was 0.041 mmol/L with the P value of 0.01. The mean percentage difference between the plasma and serum pyruvate of the patient group was 51% and that of the control group was 60% both of which are above the within individual biological variation (15.2%) as well as the reference change value (RCV) or critical difference for pyruvate (47%). The recovery percentage of the pyruvate on plasma was below the acceptable range (80-120%). Conclusion: There was a significant under-estimation of pyruvate in plasma compared to serum samples in both the patient and control groups and the mean percentage difference is beyond the within subject biological variation of pyruvate for clinical use. Thus the use of NaF plasma for pyruvate determination is not recommended.