Study of specimen stability for biochemical parameters

Introduction: The blood sample is collected and transported to the laboratory for analysis, during this time the samples bares 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. Aim and Objective: The aim of our study is to determine the stability of different seventeen biochemical parameters in primary collection (without separation of serum/plasma) and Secondary collection (with separation of serum/plasma) tube. Materials and Methods: Hundred patients' venous blood sample were collected in plain vacutainer and fluoride vacutainer (primary tube), set of the seventeen biochemical analytes like sodium, potassium, ionized calcium, chloride, glucose, creatinine, urea, uric acid, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, total protein, albumin, bilirubin, triglyceride, total cholesterol and HDL-cholesterol tests were analysed. Once the tests were carried out from primary tube, approximately half serum was separated into two aliquots (secondary collection tube). All tubes were stored at 2 to 8° C. After 24 hr and 48 hr again same sate of tests were performed on the same equipment. Statistical analysis was done after that. Results: Out of seventeen analytes most analytes remained stable in both primary and secondary tubes up to 48 hr at 2 to 8° C, these includes chloride, creatinine, urea, uric acid, total bilirubin, total protein, albumin. alkaline phosphatase (ALP), aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Plasma glucose decreased in both primary and secondary collection tube but concentration is within significant change limit (SCL). While serum potassium is increase 28.84% at 24 hr and 75.58% at 48 hr; concentration is also out of SCL range in primary collection tube even though samples stored at 2 - 8⁰ C. Conclusion: Most biochemical analytes will remain stable for 48 hr at 2 - 8⁰ C, only few analytes like plasma glucose and serum potassium requires stringent control before serum-clot separation.