Introduction: There is a definite sample retention policy for clinical biochemistry labs for retesting as well as testing for additional analytes. Minimum of 24 hours retention period is needed as per ISO 15189:2012 guidelines. The blood sample is collected and transported to the laboratory for analysis. During this time, the samples bear many extra-analytical factors prior to analysis. Contact time of plasma or serum with the blood cells is one of these factors because of ongoing cell metabolism as well as active and passive movement of analytes in cellular compartments. In a tertiary care hospital with a sample load of around 2500 samples per day, it is practically impossible to aliquot the separated serum after centrifugation from the primary collection tube for storage for 24 hours. Aim and Objectives: The aim of this study is to determine the stability of twenty-one different biochemical analytes in primary collection tube (without separation of serum/plasma) and secondary collection tube (with separation of serum/plasma in fresh aliquot).
Materials and Methods: Venous blood sample of 50 patients were collected in plain vacutainer and fluoride vacutainer (primary collection tube). A set of twenty-one biochemical analytes including sodium, potassium, urea, creatinine, total bilirubin, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, glucose, total protein, albumin, calcium, phosphorus, uric acid, amylase, lactate dehydrogenase, creatine kinase, triglycerides, total cholesterol, LDL-cholesterol and HDL-cholesterol were analyzed immediately after separation from clot/red cells to obtain the baseline values. Consequently, the samples were divided into two tubes, one being the primary collection tube (without separation of serum/plasma) and secondary collection tube (with separation of serum/plasma in fresh aliquot). All tubes were stored at 4°C ± 2°C. After 24 hours, same set of tests were done on the same equipment and statistical analysis was done.
Results: Using the SCL approach to determine the relevant clinical changes in concentration of these 21 biochemical analytes, the present study observed that concentration of serum potassium, phosphorous, lactate dehydrogenase and plasma glucose changed significantly in the primary collection tube as compared to the secondary collection tube Conclusion: Most routine biochemical analytes are stable and can tolerate a delay in separation of serum from clot for upto 24 hours when stored at 4°C ± 2°C except potassium, glucose, phosphorus and LDH.
