What is being tested? Glucose is a simple sugar, which is the main source of energy for the body. The carbohydrates we eat are broken down into glucose, among other sugars. Glucose is absorbed by the small intestine, and then circulated through the body.

Glucose is vital for energy production; the brain and nervous system cells rely on glucose and can only function when the glucose levels in the blood remain within a certain range.

The body cannot use glucose without the help of insulin. Insulin is a hormone produced by the pancreas and acts as a ‘vehicle’ to control the transport of glucose into the body’s cells. After a meal, the blood glucose level rises, and insulin is excreted from the pancreas to lower it. The amount of insulin that is released is dependent upon the content of the meal.

This test may be used as part of a routine examination in people with increased thirst, increased urination, tiredness, blurred vision, slow healing infections, sweating, trembling, anxiety, confusion, fainting episodes, diabetes management or initial diagnosis, impaired conscious level and diarrhoea and vomiting. Blood glucose monitoring is also recommended in nil by mouth patients receiving only IV fluids for longer than 12 hours, post-operative patients, patients on medications that are known to affect blood sugar levels such as diazoxide, and patients with metabolic or endocrine conditions. Neonatal factors that might require blood glucose testing include intrauterine growth retardation, pre-term infants, infants of insulin-dependent mothers, or hypothermic babies.

A blood sample is required to complete this test. First, wash and ensure the chosen site is clean and free from glucose contamination. A drop of blood is taken from a finger/toe by using a small lancet needle. The blood is then ‘absorbed’ onto a glucose test strip, and a device called a glucose meter is used to measure the glucose in the blood.

In each test strip, a chemical called glucose oxidase reacts with the glucose in the blood sample and creates an acid called gluconic acid.

The glucose meter then runs an electronic current through the blood sample on the strip, and this determines how much glucose is in the sample. This number is then relayed on the screen of the device, telling you the patient’s blood glucose level.

The blood sugar level is the amount of glucose present in the blood. The reading obtained is expressed as millimoles per litre (mmol/l). The normal blood sugar level in people with stable blood sugars is 4–8 mmol/l.

A high blood sugar level is known as hyperglycaemia, i.e., a reading above 8 mmol/litre. There are several reasons for high blood glucose levels, including infection, stress, medication use, such as steroids, increased consumption of certain food stuffs such as cakes and biscuits, and if the patient is diabetic, then insufficient medication or problems with the injection technique or injection sites.

A low blood sugar level is known as hypoglycaemia, i.e. a reading less than 4 mmol/litre. The reasons for low blood sugar can include fasting or skipped meals, increased or unexpected exercise, alcohol intake, dehydration, and if the patient is diabetic, then too much insulin or problems with the injection technique or injection sites.

Bodily functions rely on the use of glucose for energy. Sudden episodes of high or low blood sugars can be life-threatening and can cause organ failure, brain damage, coma and death.

High blood glucose levels present in the blood can damage the blood vessels. Over a sustained period of time, poorly controlled blood sugar levels can increase your chances of damaging the blood vessels. Blood glucose monitoring in diabetic patients is often performed by specialist practitioners.