Received on February 14, 2008
Accepted on June 18, 2008

Point-of-Care Testing

Use of Colorimetric Test Strips for Monitoring the Effect of Hemodialysis on Salivary Nitrite and Uric Acid in Patients with End-Stage Renal Disease: A Proof of Principle

¹ Department of Chemistry, Tufts University, Medford, MA
² Department of Medicine, Boston University School of Medicine, Boston, MA
³ Department of Periodontology and Oral Biology, Boston University Goldman School of Dental Medicine, Boston, MA
⁴ Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA

^* To whom correspondence should be addressed. E-mail: david.walt{at}tufts.edu.

BACKGROUND: Initial screening of potential biomarkers for monitoring dialysis was performed with saliva samples collected from patients with end-stage renal disease (ESRD). A more thorough analysis of the most promising markers identified in the initial screening was conducted with saliva samples acquired at hourly intervals throughout dialysis to monitor analyte concentrations as dialysis progressed. We observed that salivary nitrite (NO₂^-) and uric acid (UA) concentrations consistently decreased as dialysis proceeded.

METHODS: Solution-based colorimetric-detection chemistries for NO₂^- and UA were converted to a test strip format to produce a simple method for semiquantitatively measuring NO₂^- and UA concentrations in the clinic or at the patient's home. We assessed the test strips with saliva samples collected from both ESRD patients undergoing dialysis and healthy control volunteers to qualitatively monitor the effect of dialysis on salivary NO₂^- and UA. We used computer software to analyze digital images of the resulting test strip color intensities.

RESULTS: Test strip measurements showed that mean salivary concentrations of NO₂^- and UA were decreased in ESRD patients by 86% and 39%, respectively, compared with 15% and 9% for time-matched controls. Comparison of test strip results with calibrated solution-based assays suggests that the test strips can semiquantitatively measure salivary concentrations of NO₂^- and UA.

CONCLUSIONS: The colorimetric test strips monitored changes in salivary NO₂^- and UA concentrations that occurred in ESRD patients during dialysis. The test strips may prove useful for noninvasively evaluating dialysis progress and may also be useful for monitoring renal disease status.