Diagnosis and monitoring of diabetes mellitus
Blood glucose
The diagnosis and monitoring of diabetes continues to be centred around glucose. Two measurements are widely performed: direct measurement of glucose itself, and glycated haemoglobin, a modified form of haemoglobin, the concentration of which is proportional to the prevailing glucose concentration over a period of time. It should be clear from the section on glucose metabolism and diabetes mellitus (pp. 62–63), however, that although many features of diabetes are related to hyper- and hypoglycaemia, it is, pathologically, a much wider metabolic disorder.
Diagnosis of diabetes mellitus
Criteria for diagnosis
The current World Health Organization criteria for diagnosing diabetes mellitus are shown in Table 32.1. The figures shown apply to the concentrations found in venous plasma; slightly different figures (not shown) apply to whole blood or capillary samples. Glucose is routinely measured in blood specimens that have been collected into tubes containing fluoride, an inhibitor of glycolysis. Because of the need sometimes to obtain rapid blood glucose results and the widespread self-monitoring of diabetic patients, blood glucose may also be assessed outside the laboratory using devices such as those shown in Figure 32.1. The fasting and 2-hour criteria define similar levels of glycaemia above which the risk of diabetic complications increases substantially.
Fasting blood glucose
A fasting blood glucose concentration of ≥7.0 mmol/L is regarded as diagnostic of diabetes, whether or not hyperglycaemic symptoms are present. The patient should be fasted overnight (at least 10 hours). If the result falls between 6.0 and 6.9 mmol/L, the patient is said to have ‘impaired fasting glycaemia’ (see below). Interpretation of fasting glucose results is shown in Table 32.1.
Table 32.1
Criteria for the diagnosis of diabetes mellitus
| Fasting blood glucose | ||
| Non-diabetic | Impaired fasting glycaemia | Diabetes |
| <6.0 | 6.0–6.9 | ≥7.0 |
| Oral glucose tolerance test | ||
| Fasting | 2-hour | |
| Impaired glucose tolerance | <7.0 |
