ESPE Abstracts

Background: Hyperkalaemia, defined as potassium levels above 5.5 mmol/L, is a potentially life-threatening condition commonly seen in congenital adrenal hyperplasia (CAH). Pseudohyperkalaemia is a false elevation of potassium observed in vitro, caused by potassium moving out of cells (erythrocytes, leukocytes, or platelets) during or after blood sampling. This is often linked to high platelet counts (>450 × 10^9/L), due to potassium release from activated platelets during clotting. Confirmation involves elevated serum potassium with normal plasma potassium levels. We report two cases of infants with CAH diagnosed with pseudohyperkalaemia due to thrombocytosis.

Case 1: A term female neonate was diagnosed with salt-wasting CAH due to 21-hydroxylase deficiency, with genetic testing showing compound heterozygosity for two pathogenic CYP21A2 variants. She began hormonal replacement therapy and sodium supplements. Persistent hyperkalaemia, peaking at 6.9 mmol/L, required increased medication doses and a prolonged hospital stay. Despite maximum doses of hydrocortisone (20 mg/m²/day), fludrocortisone (150 mcg/day), and sodium chloride supplements (11 mmol/kg/day), the hyperkalaemia persisted. Suspecting pseudohyperkalaemia due to an elevated platelet count (671 × 10^9/L), it was confirmed by a serum potassium level of 6.5 mmol/L and a normal plasma potassium level of 5.1 mmol/L. After diagnosis, she was stabilized on lower doses of sodium supplements (12 mmol/kg/day) and fludrocortisone (100 mcg/day), based on plasma electrolyte levels.

Case 2: An 18-month-old girl with classic salt-wasting CAH due to 21-hydroxylase deficiency, homozygous for a pathogenic CYP21A2 deletion, was found to have elevated potassium levels (6.4 mmol/L) and thrombocytosis (663 × 10^9/L) during a routine visit. She was clinically well, and her CAH was controlled with hydrocortisone (16.3 mg/m²/day), fludrocortisone (175 mcg/day), and sodium supplements (4.3 mmol/kg/day). A repeat serum potassium test showed elevated levels (5.8 mmol/L), while plasma potassium was normal (5 mmol/L), confirming pseudohyperkalemia. She remained on the same treatment. Haematology suggested her thrombocytosis was likely due to frequent viral infections and iron deficiency anaemia.

Conclusion: Pseudohyperkalaemia should be considered in patients with CAH and thrombocytosis. To distinguish it from true hyperkalaemia, both plasma and serum potassium levels should be checked. Accurate diagnosis is crucial to avoid unnecessary interventions and hormonal dose adjustments, preventing adverse outcomes and prolonged hospital stays.