A recent study demonstrated the impact of seasonal variations in serum potassium levels on clinical decision-making and prescription patterns, particularly among patients using ACE inhibitors to manage high blood pressure.

Published in the Journal of Clinical Pathology, this time-series analysis, conducted in the UK and spanning 13 years, highlighted the need for greater awareness of the effects of ambient temperature on potassium measurements and its downstream impact on patient care.

Serum potassium tests were commonly used in clinical practice to monitor renal function and were essential for patients taking medications such as ACE inhibitors (ACEIs), which could affect potassium excretion. While the normal potassium range was between 3.5 and 5.3 mEq/L, deviations outside of this range—whether high (hyperkalemia) or low (hypokalemia)—posed serious health risks, including cardiac anomalies. For patients taking ACEIs, dose adjustment was often advised if they experienced hyperkalemia.

However, obtaining accurate potassium readings was challenging due to various factors. The study built on previous findings that ambient temperature fluctuations, particularly in colder months, caused modest but clinically significant increases in serum potassium levels during sample transportation to a centrifuge. This led to twice as many readings flagged as hyperkalemic, which triggered further clinical reviews. In many cases, clinicians recommended unnecessary interventions or adjustments to ACEI prescriptions or ordered repeat blood tests. The researchers noted that these outcomes negatively impacted patient care and clinical resources.

The study analyzed data from the IQVIA Medical Research Data (IMRD-UK), covering more than 15 million patients from 2003 to 2016. It focused on patients prescribed ACEIs or potassium supplements, with over 5.6 million ACEI prescriptions and nearly 83,000 potassium supplements issued during the study period. The researchers also incorporated temperature data from the UK Met Office to examine how ambient temperature correlated with potassium readings and prescribing patterns.

The study confirmed that serum potassium levels tended to rise during colder months, resulting in a greater number of potassium readings being classified as hyperkalemic. This seasonal variation doubled the number of tests flagged as high, which often triggered clinical reviews. As a result, doctors were more likely to reduce ACEI doses or temporarily discontinue them. Additionally, the study found a 63% reduction in potassium supplement prescriptions during these periods, highlighting the inverse prescribing pattern for hypokalemia management.

A quasi-Poisson regression analysis revealed a clear association between ambient temperature and potassium measurements, which directly influenced the likelihood of ACEI prescriptions being adjusted within 15 days of an initial prescription.

The study's findings emphasized the need for clinicians to be educated about the seasonal impact on potassium test results and to exercise caution when interpreting potassium readings, especially during colder months. Misinterpretation of elevated potassium levels could lead to unnecessary medication adjustments, potentially disrupting patient care. Furthermore, incorrect assumptions about hypokalemia might result in unwarranted potassium supplementation.

While the placement of on-site centrifuges in some UK regions reduced the impact of seasonal variation on potassium measurements, the problem persisted in many areas. The researchers suggested that broader adoption of this approach or other mitigation strategies could improve test accuracy and reduce unnecessary clinical interventions.

This study highlighted an underappreciated challenge in managing patients on ACE inhibitors, particularly in the context of seasonal changes in ambient temperature. Clinicians needed to account for these variations when interpreting potassium test results to avoid unnecessary changes in prescriptions that could negatively affect patient outcomes.

The study also noted limitations, including the inability to make patient-level inferences due to the lack of free-text medical notes and the potential influence of other blood parameters on potassium levels. Despite these limitations, the findings underscored the importance of educating clinicians on the extent of measurement errors and the potential impact on prescribing decisions.

Conflict of interest disclosures can be found in the study.