Seasonal variation of serum potassium and related prescription pattern: an ecological time series

Aims To assess if ambient temperature-related effects on serum potassium levels impact clinical decision-making. Methods This study is an ecological time series consisiting of 1 218 453 adult patients with at least one ACE inhibitor (ACEI) prescription who participate in a large UK primary care dataset.Descriptive statistics and a quasi-Poisson regression model using time series data at regular time intervals (monthly) were undertaken to examine the association between potassium measurements and ACEI/potassium supplement prescriptions. RESULTS: It is noted that correlating with lower ambient temperature, serum potassium values follow a seasonal pattern; peaks in winter months and troughs in summer. During summer months, there are clear annual spikes in the number of potassium prescriptions suggesting a change in prescribing practice during periods of potentially spurious hyperkalaemia. The converse pattern is seen in the ACEI prescription proportion which spikes annually during the winter period with lower average ambient temperatures. Our time series modelling demonstrated that each one unit increase in potassium is associated with a 33% increased rate of ACEI prescriptions (risk ratio, RR 1.33; 95% CI 1.12 to 1.59) and 63% decreased rate of potassium supplements (RR 0.37; 95% CI 0.32 to 0.43). CONCLUSIONS: Our findings highlight the seasonal pattern in serum potassium and we observe a corresponding alteration in prescribing practice for potassium sensitive medications. These findings demonstrate the importance of educating clinicians on the presence of seasonal potassium variability in addition to standard measurement error, and its potential impact on their prescribing activity.