Abstract. Kerstens MN, Guillaume CPF, Wolthers BG, Dullaart RPF (University Hospital Groningen, Groningen, The Netherlands). Gas chromatographic±mass spectrometric analysis of urinary glycyrrhetinic acid: an aid in diagnosing liquorice abuse. J Intern Med 1999; 246: 539±547.Objectives. Liquorice abuse can lead to severe clinical complications, caused by its active compound 18b-glycyrrhetinic acid (18bGA). 18bGA inhibits dehydrogenase activity of 11b-hydroxysteroid dehydrogenase (11bHSD). This enzyme catalyses the interconversion between cortisol and cortisone and normally protects the mineralocorticoid receptor from being activated by cortisol. Diagnosing liquorice abuse can be notoriously difficult. The aim of our study was to develop an accurate and clinically applicable 18bGA urinary assay. Design. We developed a urinary 18bGA assay based on gas chromatography and mass spectrometry (GCMS) with sufficient sensitivity to detect 18bGA at low concentrations. The assay was validated in four volunteers consuming different amounts of liquorice. We applied its use in two patients with hypokalaemic hypertension and suppressed plasma renin activity and serum aldosterone, who were suspected of liquorice abuse. Results. The detection limit for 18bGA of the GC assay was 10 mg L 21 , which was lowered to 3 mg L 21 by subsequent application of MS. In all volunteers, urinary 18bGA was detected during liquorice intake. Urinary 18bGA remained detectable until 5 days after stopping continued liquorice intake and until at least 51 h after ingestion of a single large amount. Urinary 18bGA was demonstrated in both patients, establishing a diagnosis of liquorice abuse. One patient showed changes in urinary cortisol metabolites, consistent with 11bHSD inhibition. Changes in cortisol metabolites were less pronounced in the other patient. Conclusion. Liquorice abuse can result in hypokalaemic hypertension with prolonged suppression of plasma renin activity and aldosterone concentration. This is caused by 18bGA-mediated inhibition of 11bHSD, resulting in activation of the renal mineralocorticoid receptor by cortisol. Urinary 18bGA measurement by GCMS is a useful aid in establishing liquorice abuse.