Perez Quartey, Quartey Perez, Orraca-Tetteh James and Seglah Richard Yawo
Background: Though serum has traditionally been the main type of sample for biochemical tests, some laboratories are increasingly using plasma now due to factors such as inadvertent clogging of auto-analyzer probes by fibrin clot in serum and delay in sample testing due to time required for blood clotting. Many previous studies on stability of biochemical analytes have mainly focused on serum with limited works on plasma.
Aim: We studied the stability of commonly used clinical biochemical analytes in human plasma including the comparative effects of storage time (0, 7, 14, 21 days) and temperature (room temperature, 4°C-8°C refrigeration temperature and -60°C) on blood separated plasma.
Methodology: Plasma samples were obtained from 6 healthy adults who are not on any medication. Urea, creatinine, sodium, potassium, total bilirubin, direct bilirubin and total protein measurements were done on freshly separated plasma sample immediately as baseline measurement. Three aliquots each were stored at room temperature on the laboratory bench, refrigerator, and -60°C freezer. Measurements were done on the stored samples on days 7, 14 and 21 and then comparatively analyzed for stability.
Results: All analytes were fairly stable in samples stored at -60°C during the study period. However, there were variations in urea, creatinine, sodium and total protein in samples stored at room temperature and refrigerator temperature. Statistically significant increases were observed in urea and creatinine with reduction in sodium after 7 days in room temperature stored samples. Similar changes were also seen in refrigerator samples after 14 days. Clinically significant changes were seen in creatinine, sodium and urea after 7 days, 14 days and 21 days respectively. Statistically significant reduction in total protein was observed in both room temperature and refrigerator samples after 14 days. Bilirubin and potassium were fairly stable in all samples during the study period.
Conclusion: Biochemical analytes are desirably stable after 3 weeks of storage in plasma separated samples at -60°C. However, there are considerable variations in stability of biochemical analytes in plasma separated samples during storage at room and refrigerator temperatures and these have to be taken into consideration in conditions of prolonged delays in analysis of samples. Additionally, the observed variations are worth investigating, in the light of inconsistencies with previously reported works, to further identify factors and mechanisms that affect the stability of biochemical analytes in plasma separated samples.