Progression From Impaired Fasting Glucose to Diabetes Mellitus Among Chinese

Impaired fasting glucose (IFG) represent an intermediate state of abnormal glucose regulation that exist between normal glucose homeostasis and diabetes mellitus (DM) and is a significant risk factor for DM and cardiovascular complications. IFG is defined by an elevated FG level between 6.1-6.9mmol/L according to the World Health Organization (WHO). The lower cutoff level for IFG was further lowered to 5.6mmol/L by the American Diabetes Association (ADA) in 2003 in order to maximize sensitivity and specificity for predicting DM over a 5-year period. In Hong Kong, IFG individuals can be more readily identified by primary care doctors than subjects with impaired glucose tolerance (IGT) or elevated HbA1c - the other 2 pre-diabetic categories - because fasting glucose (FG) test is recommended by the Hong Kong reference framework for diabetes care for adults in primary care setting for DM screening. Thus, this group of individuals should be targeted opportunistically for DM prevention.

On the other hand, IFG is a heterogeneous group with variable risk of progression to DM. Individuals with IFG may have concomitant IGT, elevated HbA1c or even DM. Thomas et al. found that around 20% of Hong Kong Chinese subjects with impaired glucose relation had concomitant IFG and IGT, whereas 49.5% had isolated IGT and 30.5% had isolated IFG. Ko et al. followed up 55 Chinese subjects with IFG for a median period of 1.12 year and showed that 8.4% progressed to DM annually as defined by fasting glucose criteria (FG ≥7.0mmol.L). Lee et al. followed up 238 Chinese women with persistent impaired glucose tolerance after gestational diabetes over a mean period of 52 months and found that 20% of the studied population developed diabetes mellitus based on OGTT criteria; the highest rate of progression to DM was noted among those women with concomitant postpartum impaired fasting glucose.

A recent cross-sectional study by Yu et al on 1,200 Chinese primary care patients with IFG demonstrated that 20% had DM confirmed by OGTT as the gold diagnostic standard, 14.3% had concomitant IGT, and 16.1% would regress back to normoglycaemia upon retest within 18 months. However, all of these local studies had short follow-up period and used different diagnostic tests for confirmation of DM; the long term risk of progression to DM among Chinese subjects with isolated IFG or combined IFG-IGT had not been fully evaluated.

Moreover, only few studies examined the risk factors for progression from IFG (+/- IGT) to DM among Asians or Chinese. Female gender, smoking, low physical activity, obesity as well as truncal obesity, high blood pressure, high triglyceridaemia and most importantly higher baseline FG level had all been reported to increase risk of progression from IFG to DM among Caucasians. In the only Asian study conducted in Japan, Toshihiro et al. found that stress in daily life, night duty and administrative position were risk factors of DM development among IFG subjects. To the best of our knowledge, no published data on the risk factors of progression from IFG to DM among Chinese is currently available. It was not certain that the risk factors identified among the Caucasians or Japanese were applicable to the Chinese. Although intensive lifestyle modifications targeting these risk factors had been reported to reduce progression from IFG to DM, their effects on Chinese subjects with IFG had not been evaluated.

Between May 2013 and March 2015, our team have already collected a prospective cohort of around 700 non-diabetic adults who have underwent both 75g OGTT and HbA1c tests as rigorous determination of their glycemic status. We aim to conduct a 3-year follow-up study to estimate the incidence of progression to DM among Hong Kong Chinese primary care patients with IFG with or without concomitant IGT using OGTT as the gold diagnostic standard as recommended by the Hong Kong Reference Framework. In addition, we aim to identify determinants, in particular the modifiable risk factors, for the progression from IFG to DM. These results will provide valuable information for designing optimal follow-up plan and diabetes prevention programme for local IFG patients, with the ultimate goal to reduce health care burden of DM on our society.

Inclusion criteria

• Aged ≥ 18 year
• Chinese ethnicity
• Diagnosis of impaired fasting glucose (i.e. FG between 5.6-6.9mmol/L) +/- impaired glucose tolerance (i.e. 2-hour postprandial PG between 7.8-11.0mmol/L) confirmed by latest OGTT results within 60 months prior to recruitment

Exclusion criteria

• Confirmed diagnosis of DM or on hypoglycaemic treatment
• Women who are pregnant or breast-feeding at recruitment
• Patients taking glucocorticoid at recruitment
• Active and uncontrolled thyroid diseases (including subjects on thyroid replacement therapy or anti-thyroid drugs) or active endocrine diseases such as Cushing's syndrome or Acromegaly at recruitment
• Severe renal impairment i.e. eGFR ≤ 30 ml/min/1.73m2
• Clinically significant anaemia at recruitment
• History of blood donation or blood transfusion within 3 months prior to recruitment