Endocrine Abstracts

Background: Bone marrow transplant (BMT) survivors are at increased risk of metabolic syndrome and developing type 2 diabetes (T2DM). Measurement of HbA1c is increasingly used in recent years for the diagnosis of T2DM. An HbA1c level of ≥6.5% (48 mmol/mol) is considered as a diagnostic cut-off for T2DM and an HbA1c between 6.0–6.4% (42–47 mmol/mol) is considered as at risk of T2DM. We aimed to look at the diagnostic performance of HbA1c and oral glucose tolerance testing (OGTT, diagnosed using WHO 1999 criteria) in identifying patients with/at risk of T2DM among long-term BMT survivors.

Materials and methods: Our study identified 129 consecutive allogeneic BMT survivors who underwent BMT at Leicester Royal Infirmary between January 1986 and December 2007. 68.2% (n=88) of the above patients were offered an appointment at late effects clinic between January 2010 and December 2012. Those who did not attend (n=30), those with known DM-2 (n=9) and who had incomplete investigations (n=4) were excluded from the study group (n=45). Data regarding demographics, medical history and drug history were recorded on the day of the visit. Factors¹ which could influence HbA1c such that it no longer reflects true glycaemic levels were investigated including levels of haemoglobin, ferritin, urea, liver function tests, and aspirin use. OGTT and HbA1c results on clinic day were reviewed.

Results: The final analysis consisted of 45 people. HbA1c results revealed 8.8% (n=4) in T2DM range (HbA1c 8.31%±1.36 (mean±S.D.)) while 24.4% (n=11) were at risk of T2DM (HbA1c 6.19%±0.13). The OGTT results revealed 8.8% (n=4) with DM-2, 2.2% each with impaired glucose tolerance (IGT) (n=1) and impaired fasting glucose (IFG) (n=1) while remaining (n=39) with normal glucose tolerance.

All the patients with abnormal OGTT (DM-2, IGT and IFG) also had abnormal HbA1c results. All the patients with HbA1c ≥6.5% 03/02/2014had abnormal OGTT results with 50% of OGTT in T2DM range while 25% with IGT and 25% with IFG.

Interestingly, patients with abnormal HbA1c in at risk range, the majority (91%, n=10) had normal glucose tolerance while the remaining 9% had IFG thus showing a large discordance in this sub-group.

Discussion: There is a large discordance between HbA1c and OGTT results in diagnosing BMT survivors at risk of T2DM. Use of an OGTT could result in a lower tendency to diagnose BMT survivors at risk of T2DM compared to an HbA1c test. Interestingly this discordance is more marked and contrary to what some other studies which focus on the general population², suggesting our finding may be a specific to BMT survivors. Given the high risk of cardiovascular mortality in this group, underdiagnoses of at risk T2DM group would delay prompt initiation of preventative measures.

References: 1. Gallagher EJ, Bloomgarden ZT & Le Roith D. Review of hemoglobin A1c in the management of diabetes. J Diabetes 2009 l 9–17.

2. Farhan S, Jarai R, Tentzeris I, Kautzky-Willer A, Samaha E, Smetana P, Jakl-Kotauschek G, Wojta J & Huber K. Comparison of HbA1c and oral glucose tolerance test for diagnosis of diabetes in patients with coronary artery disease. Source. Third department of Medicine, Cardiology an Emergency Medicine, Wilhelminen Hospital, Montleartstrasse 37, 1160 Vienna, Austria.