Aldosterone/renin ratio reliable diagnostic tool in infant primary hypoaldosteronism

By Eleanor McDermid, Senior medwireNews Reporter

The ratio of aldosterone to renin in plasma is a reliable indicator of primary hypoaldosteronism in newborns and infants, say researchers.

Using the aldosterone/renin ratio in infants, as is done in adults with suspected hyperaldosteronism, avoids the diagnosis being complicated by aldosterone levels, which may remain in the normal range. This was the case for all the nine study patients, who were treated in one of three Swiss centres.

This “can lead to misdiagnosis and delayed initiation of life-saving treatment with fludrocortisone and salt”, write Beate Rücker (University Children's Hospital Zurich, Switzerland) and co-workers in Hormone Research in Paediatrics.

The study patients were aged between 15 days and 6 months at the time of diagnosis and, notably, all came from migrant families, with eight originating from the Balkans and seven belonging to an ethnic minority group. Furthermore, seven patients had the same underlying homozygous mutation in CYP1182, implying a founder effect.

Among six patients with comparable measurements, all had elevated plasma renin levels, at an average of 304,895 mU/L, and all had aldosterone levels that were low but within the normal range, at an average of 744.5 pmol/L.

However, the aldosterone/renin ratio was below 1 pmol/mU in all patients, showing a relative reduction in aldosterone levels.

A seventh patient did not have an exact plasma renin measurement, but the researchers say that the “maximum credible value” for the aldosterone/renin ratio was less than 1.3387 pmol/mU.

The other two patients had plasma renin activity, rather than concentration, measured, but here also the ratio of aldosterone levels to renin activity was markedly below the threshold of 28 (pmol/L)/(ng/mL × h).

All patients had hyponatremia at the time of diagnosis, and seven had hyperkalemia, with another having borderline high potassium levels and the other no recorded level.

The researchers conclude that the plasma aldosterone/renin ratio “can help to diagnose this life-threatening disease faster and consequently initiate life-saving therapy earlier.”

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