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Glycaemic screening before kidney transplantation should include an oral glucose tolerance test

Year: 2026

Type: article

Abstract: Presence of diabetes mellitus (diabetes) adversely affects outcomes after kidney transplantation, and glycaemic screening should be included in the pretransplant evaluation of kidney transplant recipients. However, there is limited evidence regarding the optimal glycaemic screening protocol and current practices vary. According to diagnostic criteria defined by the American Diabetes Association, diabetes may be diagnosed based on HbA1c or plasma glucose criteria, including either fasting plasma glucose or 2-hour plasma glucose during a 75 g oral glucose tolerance test 1 (OGTT). In asymptomatic patients who fulfil diagnostic criteria for diabetes, confirmatory testing is needed to establish the diagnosis 1 .KDIGO guidelines regard OGTT as the gold standard for pretransplant assessment of glycemia 2 . However, a European survey from the ERA DESCARTES Working Group indicates that this recommendation has not been universally implemented 3 . As part of the pretransplant work-up in Norway, all kidney transplant candidates without known diabetes routinely undergo assessment with both HbA1c and OGTT.This study aimed to determine the frequency and distribution of diabetes-range HbA1c, fasting plasma glucose, and 2-hour plasma glucose results among kidney transplant recipients without known diabetes. The assessments were made according to existing pretransplant protocol at the time the patients were evaluated for waitlisting.In this retrospective observational study, patients who received a kidney transplant in Norway between 2007 and 2022 (n=3290) were identified from the national transplant registry. We excluded patients with preexisting diabetes (n=724), patients listed for re-transplantation (n=26) or combined organ transplantation (n=22) as well as patients without available HbA1c or OGTT (n=466), leaving 2052 patients eligible for the study. Data describing HbA1c and OGTT were retrieved from the patients' electronic medical records. All patients have provided signed informed consent covering this kind of analyses and the study was approved by the Regional Committee for Medical and Health Research Ethics South-East (reference 407293). During the study period 2007-2022, 5.5% of patients died while waitlisted for kidney transplantation, 11.9% were permanently withdrawn from waiting list for kidney transplantation from various reasons. Among all patients waitlisted for kidney transplantation during the study period, 12 patients (0.4%) are still waiting for kidney transplantation. American Diabetes Association criteria for diabetes were used to define diabetes range glycaemic levels: HbA1c ≥48 mmol/mol or plasma glucose ≥7.0 mmol/L, or 2-hour plasma glucose ≥11.1 mmol/L 1 .The proportion of patients fulfilling diabetes-range glycaemic levels were reported as rates or percentages and the distribution is illustrated in Figure 1 American Diabetes Association criteria for prediabetes were used to define prediabetes range glycaemic levels 1 : HbA1c from 39 to 47 mmol/mol or plasma glucose from 5.6 to 6.9 mmol/L, or 2-hour plasma glucose from 7.8 to 11.0 mmol/L.As part of the pretransplant work-up, HbA1c test and OGTT investigations were generally scheduled on a dialysis-free day, by the local nephrologist. OGTT test routines have been standardized in Norwegian hospitals throughout the study period. The OGTT was performed in the morning after at least 10 hours of fasting with oral administration of 75 grams of glucose in 200 mL of water when patients were seated and had avoided smoking the same day and were in their common medical state. They were instructed to stay on a weightmaintaining diet for 3 days prior to testing and abstain from alcohol. Plasma glucose was measured just prior to, 30 and 120 min after the glucose load and HbA1c was also assessed in a pre-OGTT sample. HbA1c analyses have been standardized in Norwegian hospitals since 2007 with standardized high-performance liquid chromatography (HPLC) or immunochemical methods certified by the IFCC in accredited laboratories. HbA1c and OGTT test results were sent to the national transplant centre as part of transplant candidate evaluation. The year of glycaemic testing, but not the exact date, was available for this study.In case of repeated tests, only the closest OGTT preformed prior to being waitlisted for transplantation were available in this analysis.This study included results from 2052 kidney transplant recipients (1354 males /66%) with mean age at transplantation 54 years (range:18-83 years) and mean BMI was 25.8 kg/m 2 (range:16.0-36.2 kg/m 2 ). Thirty percent of the patients were transplanted pre-emptively, while 47% were in haemodialysis and 23% in peritoneal dialysis before transplantation. The mean time from the OGTT/HbA1c assessment to transplantation was 1.62 years (range 0-8).We identified 165 kidney transplant recipients (8%) without known diabetes with glycaemic test results within the diabetes range detected during pretransplant work-up. Out of these, 48 patients fulfilled the HbA1c criterion, 23 patients the fasting plasma glucose criterion while 122 fulfilled the 2-hour plasma glucose criterion (Figure 1). In 23 cases, more than one diagnostic criterion was met. Baseline BMI was comparable between included and excluded patients, but excluded patients were on average five years younger than those included.Additional data are available in supplementary material.If 2-hr glucose tests results were excluded, only 65 patients (39%) were found to have glycaemic test results within the diabetes range. This approach with HbA1c and/or fasting plasma glucose assessment only, revealed 39% of the cases compared to when 2-hour plasma glucose data were included in the analyses.Among the remaining 1887 patients without diabetes-range glycaemic test results, 976 patients (52%) had test results within range of prediabetes according to one or several ADA criteria (HbA1c criterion n=514, fasting glucose criterion n= 417, 2-hour plasma glucose criterion n= 449).The main finding of our study was that 8% of Norwegian kidney transplant recipients without known diabetes were identified at the time for waitlisting with pretransplant diabetes-range glycaemic levels. These findings are in accordance with the results from two smaller studies from Austria (n=138) and Spain (n=186) which detected 3% and 6% respectively with diabetes-range screening results among their patients waitlisted for kidney transplantation [4][5] .In our study, the vast majority (74%) were identified through the 2-hour plasma glucose criterion. These patients would likely have been missed for further diagnostics and follow-up if the pre-waitlisting OGTT screening had not been included. While some transplant centres prefer fasting glucose and HbA1c and not OGTT in this clinical setting, our findings support the inclusion of OGTT as the gold standard for pretransplant glucose assessment as recommended in KDIGO guidelines 2 . Discrepancies between HbA1c and OGTT test results have also been described in the general population 6 and among kidney transplanted patients 7 . Additionally, it is known that HbA1c has its limitations to correctly reflect glycaemia in patients with chronic kidney disease 8 . In the present study, we lack information on whether the pre-waitlisting test findings triggered a follow-up re-test and/or treatment of diabetes or preventive efforts in prediabetes, and we suggest that such measures should be implemented. Hyperglycaemia identified before transplantation can be used to discuss a tailored approach to lifestyle or pharmacological interventions, when appropriate. In cases of overweight/obesity, weight loss can prevent diabetes to develop but also put diabetes into remission when identified early 9 . Since both prediabetes and diabetes are associated with increased mortality and cardiovascular risk after kidney transplantation [10][11] , pretransplant OGTT test results can be utilized in a continuous risk assessment for post-transplant diabetes among other post-transplant outcomes, as recommended by the 2022 PTDM Consensus Meeting 12 . Some transplant centres consider use of a less diabetogenic immunosuppressive regimen for patients at increased risk after kidney transplantation 13 .A strength of our study is the relative large national cohort of Norwegian kidney transplant recipients without known diabetes, with available HbA1c and OGTT sampled as part of systemic and standardized pretransplant work up, which allowed this study to analyse the overlap among individual screening thresholds. Our study has some limitations. Treatment data on anaemia, blood-transfusions, erythropoiesis-stimulating agents and iron supplementation were unfortunately not available for this study. Reported measurements of HbA1c and OGTT were performed only once per patient, while confirmative measurement is advocated in asymptomatic subjects before establishing a diabetes diagnosis 1 . OGTT is well known to have limited reproducibility and our study cohort included primarily data from patients who were transplanted and were predominantly Caucasian, limiting generalizability to all transplant candidates and other ethnic groups.In this cohort of kidney transplant recipients without previously known diabetes who underwent pretransplant glycaemic assessment, 8% had at least one screening result within the diabetes range. Notably, most cases were identified through the 2-hour plasma glucose criterion. These findings suggest that reliance on HbA1c and fasting plasma glucose alone may miss patients who warrant further diagnostics and follow-up for diabetes.

Source: Frontiers in Nephrology

DOI: 10.3389/fneph.2026.1849545