How to measure blood glucose

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Background

The level of glucose in the blood can be measured by applying a drop of blood to a chemically treated, disposable ‘test-strip’, which is then inserted into an electronic blood glucose meter. The reaction between the test strip and the blood is detected by the meter and displayed in units of mg/dL or mmol/L. There are a number of different types of meters available, and all are slightly different. Take care when applying the general principles described in this article to the specific glucose meter you are using.

Why measure blood glucose?

• It can be used as a screening tool for diabetes mellitus (diabetes).
• It is an important tool in the assessment of the unwell patient, especially in the young or old.
• Potentially life-threatening extremes of blood glucose can be detected to enable the patient, carer or health worker to respond to high (hyperglycaemia) and low (hypoglycaemia) blood glucose by adjusting the diet or using insulin.

When to measure blood glucose

• Blood glucose should be measured whenever your patient with diabetes is feeling unwell in any way.
• In the diabetic patient, it should be measured before surgery to ensure that the patient is not going be become unwell during surgery and/or after general anaesthetic. Measure regularly until the patient is eating and drinking normally and blood glucose is stable.
• In newly diagnosed diabetes patients, more frequent measurements are needed, until blood glucose is stable.

NOTE: Blood glucose monitoring is done to measure the concentration of glucose in the blood (glycaemia) over time, and is important in the care of patients with diabetes mellitus. Information about individual patterns of blood glucose changes, gathered through blood glucose monitoring, can be used to plan meals, activities, and at what time of day to take insulin. The better the patient’s blood glucose control, the less likely it is that the diabetes will cause damage in the body and lead to complications such as loss of vision (due to diabetic retinopathy) and amputation.

You will need

• Blood glucose monitor
• Test strips (check that they are in date and have not been exposed to the air)
• Alcohol swab
• Single-use safety lancets or lancing device
• Gloves
• Cotton wool/gauze
• Sharps box
• Control solution for calibration

Method

Apply these general principles when using the different types of electronic blood glucose meters available.

• Ask the patient to sit down and explain what you are going to do.
• Wash your hands and put on gloves.
• Choose the site for the blood sample: usually the side of a finger, but the arm or thigh may be used (change the site used if frequent measurements are needed).
• Use an alcohol swab to clean the site and let the alcohol dry.
• Insert the test strip into the monitor, following the instructions (Figure 1).
• Use a single-use lancet or a lancing device to draw blood (Figure 2) and dispose of it in a sharps container.
• Apply the blood to the testing strip (Figure 3) in the correct way: some strips need the blood drop to be over the whole of the test pad and some suck up the blood directly from the site of the bleeding.
• Place the alcohol swab (note: it will sting) or a piece of gauze over the site (Figure 4) and hold it there, or let the patient hold it there until the bleeding stops. Monitor for excess bleeding.
• Read and record the result, reporting and/or responding to abnormal readings.
• Tell the patient what the result is, explain it and discuss options.
• Dispose of all used equipment safely, in line with hospital or health care policies.