Familial pseudohyperkalaemia: An unusual cause of artefactual hyperkalaemia

Strict homoeostatic control of potassium is necessary for normal muscle and neural function, and as a result, hyperkalaemia can be life-threatening and requires timely management. Prior to treating the patient, however, it is important to determine if hyperkalaemic blood test results are authentic and not due to pre-analytical factors as treatment in this context may provoke potentially dangerous hypokalaemia. We present the case of a 47-year-old female referred for further investigation following 2 years of otherwise unexplained intermittent hyperkalaemia. Her highest recorded potassium was 8.9 mmol/L (reference interval: 3.5-5.2 mmol/L). She was otherwise healthy, not on regular medications, and asymptomatic during these episodes. There was no evidence of associated electrocardiogram (ECG) changes. She had been referred to the Emergency Department twice in 6 months due to hyperkalaemia, but these episodes resolved on repeat testing without any intervention. Further investigation revealed a significant time- and temperature-dependent increase in potassium concentration in whole blood samples, compared to a control. ABCB6 single gene testing revealed a heterozygous variant, c.1123 C>T, p. (Arg375Trp), consistent with a diagnosis of familial pseudohyperkalaemia (FP). This is an autosomal dominant condition, which results in increased efflux of potassium from red blood cells at sub-physiological temperatures. Whilst this is an ex vivo phenomenon, unless recognised it poses a clinical risk to patients as they may be treated erroneously.