Pseudohyperkalaemia caused by recentrifugation of blood samples after storage in gel separator tubes

Because hyperkalaemia above a certain level is life-threatening, erroneous interpretation of serum potassium concentration may misguide and complicate diagnostic procedures. We investigated a number of cases with pseudohyperkalaemia, which was assumed to have been caused by the recentrifugation of blood samples after storage in gel separator tubes. The time trend of serum potassium concentration was explored before (January-March 1997) and after (May-July 1997) ceasing the practice of recentrifuging blood samples after overnight storage. Next, we conducted an experiment on a volunteer's serum. The sample was divided into two groups and centrifuged once (control group) or twice (recentrifugation group). For both groups, serum potassium concentrations were measured immediately, and at 24, 48 and 72 h. For the recentrifugation group, the second centrifugation was done just before the measurement. The time series study showed that the mean serum potassium concentrations measured after overnight storage were 4.68 (95% CI: 4.60-4.76) mmol/L before and 4.14 (4.07-4.20) mmol/L after ceasing the practice of recentrifugation. The experiment showed that the mean serum potassium concentrations in the control group versus the recentrifugation group were 3.95 (95% CI: 3.89-4.01) mmol/L versus 4.05 (3.92-4.17) immediately (P=0.0979), 3.95 (3.89-4.01) versus 5.95 (5.61-6.29) at 24 h (P=0.0001), 4.13 (4.05-4.22) versus 6.90 (6.46-7.34) at 48 h (P=0.0001), and 4.22 (3.85-4.58) versus 7.61 (6.94-8.30) at 72 h (P<0.0001). Recentrifugation of blood samples after storage causes a spurious rise in serum potassium concentration to the degree of clinical significance. Clinicians and biochemists should take appropriate measures to stop this practice.