Richard A Oram1, Augustin M Brooks2, Shareen Forbes3, Stephanie Eckoldt4, Richard M Smith4, Pratik Choudhary5, Miranda J Rosenthal6, Paul Johnson7, Martin K Rutter8, Keith A Burling9, Timothy J McDonald1, James A M Shaw10, Andrew T Hattersley11. 1. NIHR Exeter Clinical Research Facility, Exeter Medical School, U.K. 2. Institute of Cellular Medicine, Newcastle University, Newcastle, U.K. 3. Royal Infirmary of Edinburgh and Endocrinology Unit, University of Edinburgh, Edinburgh, U.K. 4. Richard Bright Renal Unit, Southmead Hospital, Bristol, U.K. 5. Diabetes Research Group, King's College London, London, U.K. 6. Diabetes Service Royal Free London NHS Foundation Trust, U.K. 7. Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford, U.K. 8. Endocrinology and Diabetes Research Group, Institute of Human Development, Faculty of Medical and Human Sciences, University of Manchester, Manchester, U.K.Manchester Diabetes Centre, Central Manchester University Hospitals NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, U.K. 9. NIHR Cambridge Biomedical Research Centre, Core Biochemical Assay Laboratory, Cambridge, U.K. 10. Institute of Cellular Medicine, Newcastle University, Newcastle, U.K. a.t.hattersley@ex.ac.uk jim.shaw@ncl.ac.uk. 11. NIHR Exeter Clinical Research Facility, Exeter Medical School, U.K. a.t.hattersley@ex.ac.uk jim.shaw@ncl.ac.uk.
Abstract
OBJECTIVE: Islet graft function is defined by serum C-peptide in a standardized challenge test. We assessed whether urine C-peptide creatinine ratio (UCPCR) sent from home could provide a viable alternative. RESEARCH DESIGN AND METHODS: Seventeen islet recipients provided 90-min serum C-peptide (sCP90) and 120-min UCPCR (UCPCR120) samples during 68 interval posttransplant mixed-meal tolerance tests, also posting from home a 120-min postbreakfast UCPCR sample every 2 weeks. UCPCR was compared with a clinical score of islet function, derived from HbA1c and insulin dose. RESULTS: UCPCR120 and mean home postmeal UCPCR were strongly correlated with sCP90 (r(s) = 0.73, P < 0.001; and rs = 0.73, P < 0.01, respectively). Mean home UCPCR increased with clinical score (r(s) = 0.75; P < 0.001) and with graft function defined both by sCP90 >200 pmol/L and insulin independence. UCPCR cutoffs to detect insulin independence and poor graft function were sensitive and specific. CONCLUSIONS: Home UCPCR provides a valid measure of C-peptide production in islet transplant recipients.
OBJECTIVE: Islet graft function is defined by serum C-peptide in a standardized challenge test. We assessed whether urine C-peptide creatinine ratio (UCPCR) sent from home could provide a viable alternative. RESEARCH DESIGN AND METHODS: Seventeen islet recipients provided 90-min serum C-peptide (sCP90) and 120-min UCPCR (UCPCR120) samples during 68 interval posttransplant mixed-meal tolerance tests, also posting from home a 120-min postbreakfast UCPCR sample every 2 weeks. UCPCR was compared with a clinical score of islet function, derived from HbA1c and insulin dose. RESULTS: UCPCR120 and mean home postmeal UCPCR were strongly correlated with sCP90 (r(s) = 0.73, P < 0.001; and rs = 0.73, P < 0.01, respectively). Mean home UCPCR increased with clinical score (r(s) = 0.75; P < 0.001) and with graft function defined both by sCP90 >200 pmol/L and insulin independence. UCPCR cutoffs to detect insulin independence and poor graft function were sensitive and specific. CONCLUSIONS: Home UCPCR provides a valid measure of C-peptide production in islet transplant recipients.