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Kidney Week

Abstract: TH-PO1120

Thiazide Test in CKD: Variable Test Results Due to Differences in Thiazide Excretion

Session Information

Category: Fluid, Electrolytes, and Acid-Base

  • 704 Fluid, Electrolyte, Acid-Base Disorders

Authors

  • Bech, Anneke, Radboud University Nijmegen Medical Center, Nijmegen, Nijmegen, Gelderland, Netherlands
  • Nijenhuis, Tom, Radboud university medical center, Lent, Gelderland, Netherlands
  • Wetzels, Jack F., Radboud University Medical Center, Nijmegen, Netherlands
Background

The thiazide test is used to test the functionality of the sodium-chloride co-transporter (NCC). The test is used in the diagnostic work-up of patients with suspected Gitelman syndrome. Reference values for the thiazide test are based on small studies in young healthy volunteers. Patients presenting with tubular disorders however frequently are older and/or have a compromised kidney function. We observed a lower increase in fractional chloride excretion (delta FeCl) in patients with CKD and a remarkable variation in this parameter. In this study, we evaluated urinary thiazide excretion as an explanatory variable.

Methods

We performed thiazide tests in 10 individuals with CKD. Mean age was 65 years, mean serum creatinine was 124 µmol/l and seven individuals were male. Hydrochlorothiazide was measured in urine samples by LCMS.

Results

The median delta FeCl was 2.1% (range 0.0-3.9%). In 7 patients with CKD, the delta FeCl was below our threshold of 2.5% in healthy volunteers. CKD patients had a lower median thiazide excretion than young healthy individuals (33 µg/min vs 65 µg/min, p=0.01). There was a correlation between thiazide excretion and chloride excretion (Figure).

Conclusion

The standard thiazide test cannot be used in patients with CKD to evaluate the function of NCC. Our study indicates that invalid test results are likely explained by reduced tubular secretion of hydrochlorothiazide. Additional studies are needed to see if e.g. chloride excretion factored for thiazide excretion is a useful alternative parameter.

Figure: urine hydrochlorothiazide concentration at maximal FeCl (closed circles CKD subjects, open squares young healthy individuals)