Re-evaluation Of The Optimal Cutoff Of Saline Infusion Test In Diagnosis Of Primary Aldosteronism

Objective:Primary aldosteronism?PA?is one of the a common cause of secondaryhypertension.The diagnostic process for primary aldosteronism comprises screening,confirmation andsubtype classification.The diagnosis of primary aldosteronism usually requires at least one confirmatory test.The Fludrocortisone suppression test?FST?is considered to be the most reliable confirmatory test for PA.However,evidencefromthe optimal cutoff in diagnosis of PA studiesofthe salineinfusiontesthas provided conflictingresults.This study aimed to assess the diagnostic value of saline infusion test?SIT?and its optimal cutoff in diagnosis of PA,and to analyze whether the dietary salt intake affects the SIT accuracy.Methods:This is a prospective study.Two hundred and seventy-two hypertensive patients with high riskofPA wereenrolled,who were admitted to the First Affiliated Hospital of Chongqing Medical University from January 2014 to August 2017.The general clinical information of all subjects was collected.The weight,height,waist circumference,systolic blood pressure were measured.Fasting plasma glucose,serum lipid,serum sodium,serumpotassium,24h urinary potassium,24h urinary sodium,plasma corticosteroid rhythm,serum catecholamine metabolite were detected.All patients underwent the screening test,SIT and the FST in separate days.Plasma aldosterone to renin concentration ratio?ARR?was used for screening,Plasma aldosterone concentration?PAC?and Plasma renin concentration?PRC?weredeterminedwiththeautomated chemiluminescentimmunoassayforallpatients.The diagnosis of PA was established according to the FST criteria in this study,All collected patients were divided into PA group and essential hypertension?EH?group.Receiver operating characteristic?ROC?analysis was performed to compare diagnostic accuracies for PA,using the PAC of post-SIT,the ARR of post-SIT and the PAC suppression percentage of post-SIT,respectively.According to the Youden?s Index,the optimal cutoff point diagnosis of PA were determined.Meanwhile,according to the 24h urinary sodium level,the patients were divided into low salt,normal salt and high salt groups respectively,the effect of salt intake to SIT was analyzed.Results:Finally,In 236 patients with high riskofPA who completed the SIT and FST confirmatory test,134 patients with PA and102 patients with EH were diagnosed.Using post-SIT plasma aldosterone concentrationfor diagnosis,the areas under the receiver operator characteristics curves(AUC_ROC)of the SIT was 0.974?95%CI:0.957 to0.991,P<0.01?,which was significantly higher than that of the post-SIT plasma aldosterone to renin concentration ratio?ARR?[0.900?95%CI:0.862 to 0.938,P<0.01?and that of the post-SIT PAC suppression percentage[0.752?95%CI:0.690 to 0.813,P<0.01?],?P<0.01?.Considering both sensitivity and specificity,an optimal cutoff of PAC post-SIT was set at 8 ng/dl,resulting in a sensitivity of 88.1%and a specificity of 95.1%.The PAC post-SIT,whether in PA or EH patients,had no statistically significant differences among low salt,normal salt and high salt groups?P>0.05?.Conclusions:SIT is a reasonably good alternative to the more expensive and complex FST for the diagnosis of PA.Among the post-SIT plasma aldosterone concentration,post-SIT plasma aldosterone to renin concentration ratio and post-SIT PAC suppression percentage,PAC post-SIT was reliable for the diagnosis of PA.PAC post-SIT more than 8.0ng/dl was recommended to confirm PA.The accuracy of the SIT for the diagnosis of PA was unaffected by salt intake.