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Abstract: FR-PO314

Assessment of the Feasibility of Measuring Salivary Urea by Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy to Diagnose and Stage CKD

Session Information

Category: CKD (Non-Dialysis)

  • 2102 CKD (Non-Dialysis): Clinical, Outcomes, and Trials


  • Lin, Tzu-Ling, University College London, London, United Kingdom
  • Evans, Rhys David Russell, University College London, London, United Kingdom
  • Unwin, Robert J., University College London, London, United Kingdom
  • Norman, Jill T., University College London, London, United Kingdom
  • Rich, Peter R., University College London, London, United Kingdom

Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy has been shown to provide a straightforward, reagent-free method for the staging and diagnosis of different diseases including pancreatic cancer, and kidney stones. Recently, disposable ATR-FTIR internal reflection elements have been developed. It is plausible, given further advancements, for this technology to be miniaturised and utilised in portable diagnostic devices. Previous studies have shown a correlation between salivary and serum urea in chronic kidney disease (CKD) patients. However, these studies employed costly, labour-intensive commercial kits which limits wider applicability, therefore we assessed the feasibility of ATR-FTIR spectroscopy as an alternative method to measure salivary urea in patients with different stages of CKD.


The ATR-FTIR spectra of dried saliva samples from 6 healthy controls and 20 CKD patients (stage1-5) were recorded and analysed to provide their urea concentrations in the clinically-relevant range. The correlation between salivary urea and serum urea was also determined. The diagnostic performance of ATR-FTIR spectroscopy to diagnose CKD was assessed from the sensitivity and specificity parameters of a receiver operating characteristics (ROC) curve analysis.


The limit of detection of salivary urea by ATR-FTIR spectroscopy is 2 mM. Statistically significant differences in salivary urea concentration were demonstrated between healthy subjects (4.6±1.4 mM) and CKD patients stages 3-5 (CKD 3: 6.8±0.7 mM, p<0.05; CKD 4: 9.1±1 mM, p<0.001; CKD 5: 14.8±1.6 mM, p<0.001). However, no significant differences were detected between CKD stage 1-2 and healthy controls. ROC analyses (the value ranging from 0.95-1) confirmed the suitability of the method for determination of salivary urea concentrations in the clinically-relevant range, with the sensitivities of 0.86-1 and specificities of 0.93-1.


This study showed that salivary urea can be measured by ATR-FTIR spectroscopy with significant differences in salivary urea levels between CKD stage 3-5 and normal subjects. The development of simple single-use ATR-FTIR spectroscopy devices may be a screening tool for rapid quantitation of salivary urea to diagnose CKD.