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A Thiazide Test for the Diagnosis of Renal Tubular Hypokalemic Disorders

Giacomo Colussi^*,, Alberto Bettinelli, Silvana Tedeschi, Maria Elisabetta De Ferrari, Marie Louise Syrén^,||, Nicolò Borsa, Camilla Mattiello, Giorgio Casari^¶, and Mario Giovanni Bianchetti^**

^* Unité Operative Nefrologia, Ospedale di Circolo e Fondazione Macchi, Varese, Italy; Unité Operative Nefrologia, Dialisi e Trapianto Renale, Ospedale Niguarda-Ca' Granda, Milano, Unité Operative Pediatria, Ospedale Mandic, Merate (Lecco), Laboratorio di Genetica Medica, Fondazione IRCCS Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, Milano, ^|| Istituto di Pediatria e Neonatologia, Università degli Studi di Milano, Milano, and ^¶ Unità di Genetica Molecolare Umana, DIBIT, Istituto Scientifico San Raffaele, Milano, Italy; and ^** Servizio di Integratio di Pediatria, Mendrisio e Bellinzona, Switzerland

Address correspondence to: Dr. Giacomo Colussi, U.O. Nefrologia, A.O. Ospedale di Circolo e Fondazione Macchi, Viale Borri, 57, 21100 Varese, Italy. Phone: +39-332-278208; Fax: +39-332-393018; E-mail: giacomo.colussi{at}ospedale.varese.it

Although the diagnosis of Gitelman syndrome (GS) and Bartter syndrome (BS) is now feasible by genetic analysis, implementation of genetic testing for these disorders is still hampered by several difficulties, including large gene dimensions, lack of hot-spot mutations, heavy workup time, and costs. This study evaluated in a cohort of patients with genetically proven GS or BS diagnostic sensibility and specificity of a diuretic test with oral hydrochlorothiazide (HCT test). Forty-one patients with GS (22 adults, aged 25 to 57; 19 children-adolescents, aged 7 to 17) and seven patients with BS (five type I, two type III) were studied; three patients with "pseudo-BS" from surreptitious diuretic intake (two patients) or vomiting (one patient) were also included. HCT test consisted of the administration of 50 mg of HCT orally (1 mg/kg in children-adolescents) and measurement of the maximal diuretic-induced increase over basal in the subsequent 3 h of chloride fractional clearance. All but three patients with GS but no patients with BS and pseudo-BS showed blunted (<2.3%) response to HCT; patients with BS and the two patients with pseudo-BS from diuretic intake had increased response to HCT. No overlap existed between patients with GS and both patients with BS and pseudo-BS. The response to HCT test is blunted in patients with GS but not in patients with BS or nongenetic hypokalemia. In patients with the highly selected phenotype of normotensive hypokalemic alkalosis, abnormal HCT test allows prediction with a very high sensitivity and specificity of the Gitelman genotype and may avoid genotyping.