A Few Steps Closer to Optimizing Pseudohyperkalemia Detection

Pseudohyperkalemia and the Need for Imperative Caution With the Newly Introduced Potent Potassium Binders: Two Cases

Pseudohyperkalemia was first reported in 1955 by Hartmann and Mellinkoff, as a marked elevation of serum potassium in the absence of clinical evidence of electrolyte imbalance - simultaneous serum potassium exceeds plasma potassium by >0.4 mmol/L. We describe two patients with pseudohyperkalemia who inadvertently received inappropriate potassium binder therapy for weeks to months before the diagnosis of pseudohyperkalemia was entertained and subsequently confirmed. Potassium binders ultimately were promptly discontinued once the diagnosis of pseudohyperkalemia was confirmed. Physicians’ attention must be drawn to the availability of the new potent oral potassium binders, patiromer and sodium zirconium cyclosilicate. We strongly advocate for imperative caution with these new binders. Iatrogenic life-threatening hypokalemia remains a real concern and must be avoided. Our patients highlighted the importance of caution in the use of the newer potent potassium binders to mitigate against the causation of iatrogenic hypokalemia. Also as important is the observation that in the same patient, with changing clinical scenarios, a patient might exhibit true hyperkalemia that alternated with pseudohyperkalemia, the first of such a report.

The potential role of the eGFR in differentiating between true and pseudohyperkalaemia

BACKGROUND

Differentiating between true and pseudohyperkalaemia is essential for patient management. The common causes of pseudohyperkalaemia include haemolysis, blood cell dyscrasias and EDTA contamination. One approach to differentiate between them is by checking the renal function, as it is believed that true hyperkalaemia is rare with normal function. This is logical, but there is limited published evidence to support it. The aim of this study was to investigate the potential role of the estimated glomerular filtration rate in differentiating true from pseudohyperkalaemia.

METHODS

GP serum potassium results >6.0 mmol/L from 1 January 2017 to 31 December 2017, with a repeat within seven days, were included. Entries were retrospectively classified as true or pseudohyperkalaemia based on the potassium reference change value and reference interval. If the initial sample had a full blood count, it was classified as normal/abnormal to remove blood cell dyscrasias. Different estimated glomerular filtration rate cut-points were used to determine the potential in differentiating true from pseudohyperkalaemia.

RESULTS

A total of 272 patients were included with potassium results >6.0 mmol/L, with 145 classified as pseudohyperkalaemia. At an estimated glomerular filtration rate of 90 ml/min/1.73 m², the negative predictive value was 81% (95% CI: 67-90%); this increased to 86% (95% CI: 66-95%) by removing patients with abnormal full blood counts. When only patients with an initial potassium ≥6.5 mmol/L were included (regardless of full blood count), at an estimated glomerular filtration rate of 90 ml/min/1.73 m², the negative predictive value was 100%. Lower negative predictive values were seen with decreasing estimated glomerular filtration rate cut-points.

CONCLUSION

Normal renal function was not associated with true hyperkalaemia, making the estimated glomerular filtration rate a useful tool in predicting true from pseudohyperkalaemia, especially for potassium results ≥6.5 mmol/L.