Hypothesis: A simple algorithm to distinguish between hypoaldosteronism and renal aldosterone resistance in patients with persistent hyperkalemia

AIM: Many patients with hyperkalemia have a readily identifiable cause, which leads to appropriate management. In others, particularly those with a reduced glomerular filtration rate, differentiating between (relative) hypoaldosteronism (HA) and renal aldosterone resistance (RAR) can be problematic. The aim of this study was to see if a plasma aldosterone to potassium algorithm could be defined which would help identify patients with hyperkalemia owing to suboptimal levels of aldosterone, thereby validating treatment with 9-alpha-fluhydrocortisone, instead of cation exchange resins, if more conservative treatment fails. METHODS: A literature search for, and analysis of, studies providing details of plasma aldosterone and plasma potassium in normals (made hyperkalemic)and patients with a plasma potassium >5.3 mmol/L, and a contemporaneous plasma aldosterone. RESULTS: One study was found in which normals were made significantly hyperkalemic (to 6.3 mmol/L). These subjects, while on a high sodium, low potassium (western) diet (n = 5), provided an arbitrary definition of a simple aldosterone to potassium algorithm for diagnosis (factored aldosterone (FAldo) = plasma aldosterone/(plasma K - 4.2)). The limit for FAldo is set at 280(pmol/L) or 10(ng/dL): results below the limit suggest HA; above the limit, RAR. This algorithm was then tested against, and, when plasma potassium was greater than 5.3, found to be consistent with, reported patients with confirmed HA (n = 33) and pseudohypoaldosteronism (n = 23). The ratios in reported patients with renal failure (n = 43) were consistent with either HA (n = 30) or RAR(n = 13). HYPOTHESIS: In hyperkalemic patients a plasma aldosterone to potassium algorithm may help distinguish HA from RAR, thereby guiding therapy.