Hyperkalaemia in a female patient with systemic lupus erythematosus: questions

Abstract

Our patient initially presented with lupus nephritis and hyperkalaemia, with a normal anion gap and hyperchloraemic metabolic acidosis. A wide range of conditions have to be taken into account in the differential diagnosis for hyperkalaemia. Based on our patient’s laboratory findings, acute renal failure, drugs, blood transfusion and hemolysis were ruled out. Persistent hyperkalaemia and normal anion gap metabolic acidosis led us to suspect the presence of Type 4 RTA. This is included in the general classification of RTA as its cardinal feature is hyperkalaemia with a mild (normal anion gap) metabolic acidosis and normal measured urinary acidification [1]. Unlike distal RTA, in which proton secretion is defective, causing high urine pH, the main defect in Type 4 RTA is transport abnormality of the distal tubule, which is secondary to aldosterone deficiency, resistance or inhibition. The primary effect of aldosterone on the collecting duct is to stimulate sodium reabsorption and potassium secretion in principle cells, which results in an increase in the negative electrical potential of the lumen, promoting proton secretion. Aldosterone also directly affects the alpha intercalated cells to promote proton secretion by upregulating the expression of the proton ATPase as well as carbonic anhydrase. Thus, patients that are aldosterone deficient or resistant to aldosterone have increased sodium excretion [1, 2]. Our patient also had mildly increased of sodium excretion. The preferred method to estimate potassium excretion by the distal tubule is the TTKG. Our patient’s TTKGwas 5 in the presence of hyperkalaemia (normal >10), which indicates a defect in potassium secretion. A low TTKG is associated with aldosterone deficiency or resistance. The renin activity was 2.3 (5–27.8) pg/mL and the aldosterone level was 10 (13–340) pg/ L in the presence of high plasma levels of potassium. She appeared to have two distinct disorders, namely, renin– aldosterone deficiency or hyperkalaemic distal RTA. Her urine pH was 5.5 when the blood pH was 7.3, and the HCO was 16.8 mEq/L, which are suggestive of hyporeninaemic hypoaldosteronism (Type 4 RTA). Type IV RTA is the most common form of renal tubular acidosis and occurs in various disorders (Table 1). The most common causes of HH include diabetic nephropathy, tubulointerstitial disease and, in particular, interstitial nephritis associated with non-steroidal anti-inflammatory drugs (NSAIDs). Other causes in which hypoaldosteronism is present but not matched by hyporeninism include adrenal destruction (whether surgical, malignant or hemorrhagic), This article refers to the article that can be found at doi:10.1007/ s00467-2011-2040-5