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Related Experiment Videos

A modified cyanide-nitroprusside method for quantifying urinary cystine concentration that corrects for creatinine

Y Nakagawa1, F L Coe

  • 1Department of Biochemistry & Molecular Biology, and Kidney Stone Program, Department of Medicine, University of Chicago, Chicago, IL 60637, USA. ynakagaw@medicine.bsd.uchicago.edu

Clinica Chimica Acta; International Journal of Clinical Chemistry
|November 11, 1999
PubMed
Summary

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This study presents a reproducible colorimetric method to quantify cystine in urine, addressing limitations of previous assays for diagnosing cystinuria. The new method improves accuracy by optimizing reduction time and minimizing creatinine interference.

Area of Science:

  • Clinical Chemistry
  • Urology
  • Biochemistry

Background:

  • Cystinuria diagnosis relies on detecting urinary cystine.
  • Qualitative colorimetric tests exist, but quantitative methods lack reproducibility.
  • Previous quantitative assays were hindered by insufficient reduction times and creatinine interference.

Purpose of the Study:

  • To develop a reproducible colorimetric method for quantitative cystine analysis in urine.
  • To identify and overcome factors causing non-reproducible results in prior cystine assays.

Main Methods:

  • A modified colorimetric method was developed to quantitate urinary cystine.
  • Key factors like reduction time and interfering substances (creatinine, ascorbic acid, ferric chloride) were investigated.
  • Urine samples from normal individuals and cystinuria patients were analyzed.

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Main Results:

  • The developed method demonstrated improved reproducibility for cystine quantification.
  • Ascorbic acid and ferric chloride were identified as interfering agents in the color reaction.
  • Captopril exhibited a dose-dependent response, while Thiola and D-penicillamine had minimal impact on cystine determination.

Conclusions:

  • A reliable colorimetric method for quantifying urinary cystine has been established.
  • Understanding and controlling reaction conditions and interfering substances are crucial for accurate cystine measurement.
  • This method offers potential for improved diagnosis and monitoring of cystinuria.