Endocrine 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 diagnosed with salt-wasting CAH due to 21-hydroxylase deficiency (compound heterozygosity for two pathogenic CYP21A2 variants) began hormone replacement therapy and sodium supplements. Persistent hyperkalaemia, peaking at 6.9 mmol/l, necessitated increased medication doses and a prolonged hospital stay. Despite maximum doses of hydrocortisone (20 mg/m²/day), fludrocortisone (150 mg/day), and sodium chloride supplements (11 mmol/kg/day), hyperkalaemia persisted. Suspecting pseudohyperkalaemia due to an elevated platelet count (671× 10^9/l), this was confirmed with serum potassium at 6.5 mmol/l and normal plasma potassium at 5.1 mmol/l. She was stabilized on lower doses of sodium supplements (12 mmol/kg/day) and fludrocortisone (100 mg/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) had elevated potassium levels (6.4 mmol/l) and thrombocytosis (663 × 10^9/l) during a routine visit. Clinically well, her CAH was controlled with hydrocortisone (16.3 mg/m²/day), fludrocortisone (175 mg/day), and sodium supplements (4.3 mmol/kg/day). Repeat serum potassium testing showed elevated levels (5.8 mmol/l), while plasma potassium was normal (5 mmol/l), confirming pseudohyperkalaemia. She remained on the same treatment. Haematology attributed her thrombocytosis 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.