Seasonal pseudohyperkalaemia in primary care: are there lessons to be learnt?

Background Seasonal pseudohyperkalaemia refers to an artefactual elevation of in vitro serum potassium observed during colder weather. Primary care samples may be especially susceptible due to longer transport times at low ambient temperatures. Uncertainty about the validity of unexpected high potassium results necessitates further investigation to avoid patient harm. We evaluated whether pseudohyperkalaemia was more frequent in blood samples from primary care collected during a warm month compared to a cold month of the year. Methods A retrospective audit of samples originating from primary care practices (West Birmingham and the Black Country region, UK) in which an initial critically high serum potassium concentration of ≥ 6.5 mmol/L was reported in the months of August and November 2024. Pseudohyperkalaemia was defined as a repeat potassium measurement taken within 7 days that was ≤ 5.3 mmol/L. Results Out of 17 critical hyperkalaemia results in August and 74 in November 2024, pseudohyperkalaemia was confirmed in 7 (41.2%) and 61 (82.4%) cases, respectively. The mean (standard deviation) decrease in potassium on repeat testing in November (1.94 ± 0.75 mmol/L) was greater (P = 0.001) than in August (0.98 ± 0.94 mmol/L). The estimated glomerular filtration rate (eGFR) ≥ 60 ml/min/1.73m2 decreased the likelihood but did not abolish the possibility of genuine hyperkalaemia. Conclusions Cold weather exacerbates in vitro hyperkalaemia caused by longer transport time of primary care samples, increasing the frequency of pseudohyperkalaemia. This imposes additional pressure on stretched clinical services. Faster or temperature-controlled transport or on-site centrifugation in primary care may help mitigate this problem.