2Diabetes is characterized by high blood glucose for a prolonged period of time. In order to find a cut off value that separates diabetes from “non-diabetes” the experts looked at the incidence of diabetic retinopathy, a disorder typical of diabetes but not found in any other disease. It was found that the incidence of diabetic retinopathy goes up dramatically once the fasting venous plasma glucose crosses 120 mg/dl or so (Fig. 1.1).
In 1997 an international expert committee decided that patients with a fasting venous plasma glucose of 126 mg/dl (corresponding to 7.0 mmol/l) or more will be classified as diabetic. Fasting was defined as a fast of 8 hours or more and it was required that the test be confirmed on one more occasion. It was also stipulated that the values applied to healthy individuals, i.e. someone with acute appendicitis and a FPG of 130 mg/dl could not be called diabetic unless the value was repeated when the patient was fully recovered.
Fig. 1.1: Prevalence of retinopathy by deciles of the distribution of FPG, 2-hPG, and HbA1c in Pima Indians (A) described by McCance et al. In Egyptians (B) described by Engelgau et al, and in 40- to 74-year-old participants in NHANES III (K. Flegal, National Center for Health Statistics, personal communication). The x-axis labels indicate the lower limit of each decile group. Note that these deciles and the prevalence rates of retinopathy differ considerably among the studies, especially the Egyptian study, in which diabetic subjects were oversampled. Retinopathy was ascertained by different methods in each study; therefore, the absolute prevalence rates are not comparable between studies, but their relationships with FPG, 2-hPG, and HbA1c are very similar within each population
Source: American Diabetes Association, 2004 Guidelines.
4OGTT or oral glucose tolerance test: A post glucose value of 200 mg/dl was considered equivalent to a FPG of 126 mg/dl. The glucose had to be administered after an overnight (8 hr) fast, first thing in the morning in a dose of 75 g in adults and the sample drawn 2 hours from the time of starting the glucose ingestion. During this time the subject was required to be at rest and refrain from eating or smoking.
Three terms are in vogue at present. IFG or impaired fasting glucose where the FPG lies between 100 mg/dl and 125 mg/dl; IGT or impaired glucose tolerance when the 2 hrs PPPG lies between 140 and 199 mg/dl; GDM or gestational diabetes mellitus when diabetes was first diagnosed during a pregnancy. IFG and IGT are currently being collectively labelled as pre-diabetes.
Diabetes is basically classified as Type 1 or Type 2. In the former there is beta cell destruction usually due to autoimmune factors while in the latter there is a insulin deficiency relative to the needs of the individual. The full classification is given in Table 1.1.
GDM A screening test is advisable for all patients in the 24th to 28th week of pregnancy. This consists of a 50 g glucose load given at any time without fasting. Values over 140 mg/dl need further work up with a 100 g 3 hr OGTT (US) or a 75 g 2 hr OGTT (WHO).
Fasting 1 hr 2 hr 3 hr | 105 mg/dl 190 mg/dl 165 mg/dl 145 mg/dl |
Screening for the general public. It has been estimated that type 2 diabetes is present for 5 to 10 years before it is diagnosed, which is why many patients present with complications at diagnosis (e.g. there is symptomatic neuropathy in 25 percent of all newly diagnosed type 2 individuals.) There is no consensus on this issue but certainly high-risk individuals should be screened.
The following are considered major risk factors for type 2 diabetes:
- Previous IFG or IGT or GDM
- 1st degree relative with type 2 diabetes
- Physical inactivity
- BMI over 23 kg/m2 (Different from Western standard of 25 kg/m2)
- Hypertension (over 140/90 mm Hg)
- HDL under 35 mg/dl and or TG over 250 mg/dl
- History of delivery of a baby of birth weight over 4 kg
- Presence of polycystic ovary syndrome.
The best screening test is venous plasma glucose drawn after a 8 hr fast. Values ≥ 126 mg/dl are diagnostic of diabetes. A capillary finger prick glucose is not accurate enough. If the value is in the IFG range 8it is sometimes necessary to do a 2 hrs PPBG. This is because there is currently evidence that type 2 diabetes can be prevented or at least delayed by appropriate measures.
SPECIAL TYPES OF DIABETES IN INDIA
- Fibrocalculous pancreatic diabetes (FCPD). Here there is calcification and fibrosis in the pancreas with stone formation in the pancreatic duct. Surgical treatment is necessary if the stones cause duct dilatation and severe pancreatic pain. Management is with insulin and sometimes fairly high doses are required. FCPD is thought to be a risk factor for pancreatic cancer. It has now been classified as a disease of the exocrine pancreas. The exact etiology is yet unknown.
- Malnutrition related diabetes mellitus (MRDM). Diabetes has been thought to be due to malnutrition especially due to protein deficiency. An association between malnutrition and subsequent diabetes has been shown in human and animal studies but a true cause and effect relationship has yet to be established. Therefore the current classification of diabetes does not mention this entity.