The correlation of urea and creatinine concentrations in sweat and saliva with plasma during hemodialysis: an observational cohort study

Sophie Adelaars, Constantijn J.A.M. Konings, Lieke Cox, Eva Boonen, Massimo Mischi, R. Arthur Bouwman, Daan van de Kerkhof (Corresponding author)

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OBJECTIVES: Urea and creatinine concentrations in plasma are used to guide hemodialysis (HD) in patients with end-stage renal disease (ESRD). To support individualized HD treatment in a home situation, there is a clinical need for a non-invasive and continuous alternative to plasma for biomarker monitoring during and between cycles of HD. In this observational study, we therefore established the correlation of urea and creatinine concentrations between sweat, saliva and plasma in a cohort of ESRD patients on HD.

METHODS: Forty HD patients were recruited at the Dialysis Department of the Catharina Hospital Eindhoven. Sweat and salivary urea and creatinine concentrations were analyzed at the start and at the end of one HD cycle and compared to the corresponding plasma concentrations.

RESULTS: A decrease of urea concentrations during HD was observed in sweat, from 27.86 mmol/L to 12.60 mmol/L, and saliva, from 24.70 mmol/L to 5.64 mmol/L. Urea concentrations in sweat and saliva strongly correlated with the concentrations in plasma (ρ 0.92 [p<0.001] and 0.94 [p<0.001], respectively). Creatinine concentrations also decreased in sweat from 43.39 μmol/L to 19.69 μmol/L, and saliva, from 59.00 μmol/L to 13.70 μmol/L. However, for creatinine, correlation coefficients were lower than for urea for both sweat and saliva compared to plasma (ρ: 0.58 [p<0.001] and 0.77 [p<0.001], respectively).

CONCLUSIONS: The results illustrate a proof of principle of urea measurements in sweat and saliva to monitor HD adequacy in a non-invasive and continuous manner. Biosensors enabling urea monitoring in sweat or saliva could fill in a clinical need to enable at-home HD for more patients and thereby decrease patient burden.

Original languageEnglish
Pages (from-to)1118-1125
Number of pages8
JournalClinical Chemistry and Laboratory Medicine
Issue number6
Early online date23 Jan 2024
Publication statusE-pub ahead of print - 23 Jan 2024


Research funding: This study was funded by the Catharina Research Fund (2021-3) and Penta program (project 19017).

FundersFunder number
Catharina Research Foundation19017, 2021-3


    • biosensors for sweat analysis
    • continuous monitoring
    • diagnostics of urea in sweat and saliva
    • hemodialysis at home
    • non-invasive monitoring
    • Biomarkers/analysis
    • Humans
    • Middle Aged
    • Male
    • Creatinine/blood
    • Saliva/chemistry
    • Sweat/chemistry
    • Adult
    • Female
    • Urea/analysis
    • Aged
    • Kidney Failure, Chronic/therapy
    • Cohort Studies
    • Renal Dialysis


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