Hyperkalemia in acute glomerulonephritis due to transient hyporeninemic hypoaldosteronism

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.

Potassium homeostasis and its disturbances in children

Although only 2% of the body potassium is present in the extracellular space, its concentration is finely regulated by the internal balance, or distribution of potassium between the intracellular and extracellular compartments, and by the external balance, or difference between intake and output of potassium. Internal balance is modulated by a host of factors, including insulin, epinephrine, extracellular pH and plasma tonicity. Potassium output from the body is mainly determined by renal excretion. Renal secretion of potassium takes place predominantly in the principal cells of late distal and cortical collecting tubules, by a process involving the accumulation of potassium in the cell by the activity of the basolateral Na+,K(+)-ATPase and its exit through luminal conductive channels. The factors regulating renal potassium secretion are potassium intake, rate of tubular fluid flow, distal sodium delivery, acid-base status and aldosterone. Hypokalaemia may result from a low potassium intake, excessive gastrointestinal, cutaneous or renal losses and altered body distribution. Aetiological diagnosis and therapy are best accomplished when the acid-base status is assessed at the same time. Before establishing the diagnosis of hyperkalaemia, spurious hyperkalaemia due to haemolysis or release of potassium from cells during clot retraction (pseudohyperkalaemia) should be ruled out. Hyperkalaemia may result from exogenous or endogenous loading, decreased renal output and altered body distribution. Acute hyperkalaemia represents an emergency situation which requires immediate therapy.