Tests to measure blood sugar levels are often carried out as part of routine check-ups or for monitoring those with a pre-existing condition. There are two primary methods by which blood sugar levels are gauged. The simplest method involves pricking a fingertip and letting a drop of blood fall on the strip of a glucose meter, a handheld device to measure blood sugar levels. This incites a reaction on the strip causing electric currents to pass through and give a reading. The results can be obtained almost immediately with acceptable accuracy using this method.

The second method involves drawing a blood sample from a vein (usually at the elbow) and checking the amount glucose in the sample. This test requires the use of a clinical laboratory and the results take longer, but is more accurate than the fingerstick test mentioned above. To make the results more reliable, the blood test is often performed at different times of day i.e. in the fasting state and 2 hours after ingestion of glucose solution (oral glucose tolerance test or OGTT).

A more reliable way of checking the long-term sugar levels is to check the level of hemoglobin in the blood with glucose attached. This test, called the glycated (glycosylated) hemoglobin or HbA1c measures the average glucose levels for the past two to three months as opposed to a glucose meter or a lab glucose test which provides a reading of sugar levels at the moment of testing. The amount of HbA1c present in the blood is proportional to the sugar levels during that period.

In addition to normal individuals and those with diabetes mellitus, blood glucose testing can also unearth another category of individuals i.e. those in whom the blood sugar values are higher than normal, but not high enough to be classified as diabetes. This condition is known as “pre-diabetes” and is an important stage in the natural progression from normal to diabetes. Individuals with pre-diabetes are at high risk of progressing to diabetes, but this can be prevented or delayed by early identification and institution of lifestyle modification measures such as dietary changes and physical activity, with or without the use of medications.

Insulin is a hormone secreted by the pancreas that stimulates the absorption of glucose from the blood into the liver, muscle and fat cells. When the responsiveness of liver, muscle and fat cells to insulin decreases, it results in increased glucose levels in the blood. This deterioration in response is termed insulin resistance. The pancreas tries to mitigate the situation by producing more insulin which would maintain homeostasis. However, when the pancreas becomes incapable of keeping up with the demand or when the responsiveness of target cells further weakens, pre-diabetes occurs which in turn can progress to type 2 diabetes.

There are specific cells in the pancreas called beta-cells which are responsible for the production of insulin in the body. A genetic predisposition or certain environmental factors can cause the body to mistakenly recognize these beta-cells as foreign matter and subsequently attack them, ultimately destroying them completely. The halt in insulin production leads to high glucose levels in the blood. This form of diabetes is classified as Type 1diabetes and the treatment involves the injection of chemically synthesized insulin to maintain blood glucose levels, failing which the patient can die. This reliance on external insulin for survival is called insulin dependence.

The production of insulin by the pancreas is accompanied by the formation of a by-product called C-peptide. It is made up of 31 amino acids and plays a vital role in the diagnosis of various diseases. Since the production of C-peptide and insulin occurs in tandem, lower levels of C-peptide in the blood are indicative of Type 1 diabetes. However, even in type 2 diabetes, insulin production and C-peptide levels can decrease with time, as discussed earlier. Individuals whose C-peptide levels are low or absent will need to administer insulin to control their diabetes.

The two types of diabetes, type 1 and type 2, were initially classified as child-onset (juvenile-onset) and adult-onset diabetes respectively, however, recent observations are contrary to this observation. While type 1 diabetes usually sets in during childhood and adolescence, the onset has been reported even in the seventh decade of life. Similarly, while type 2 diabetes is typically found in adults over 45, there has recently been an increase in the numbers of adolescents and even children diagnosed with this disorder. Lifestyle, dietary habits and genetic factorsusually determine the age of onset of diabetes.