Self-monitoring of blood glucose (SMBG) is the regular measurement of blood glucose levels by patients using a portable glucometer. It is an important component of diabetes management that enables patients and healthcare providers to evaluate glycaemic control, assess the effectiveness of treatment, detect hypo- and hyperglycaemia early, and make informed decisions regarding medication, diet, and physical activity.

SMBG is particularly valuable in patients receiving insulin therapy or medications that increase the risk of hypoglycaemia. When performed correctly and interpreted appropriately, it contributes to improved glycaemic control, reduces diabetes-related complications, and promotes patient self-management.

Indications

SMBG is recommended in the following situations:

• Patients receiving insulin therapy

• Patients taking sulphonylureas or other medicines that may cause hypoglycaemia

• During pregnancy and pre-pregnancy planning

• During acute illness or infection

• Following changes in diabetes treatment

• During major lifestyle modifications affecting glucose control

• When HbA1c measurements are unreliable (e.g., haemoglobinopathies, haemolytic anaemia)

• Patients with recurrent hypoglycaemia

• Patients with poor glycaemic control requiring treatment adjustment

Objectives

The objectives of SMBG are to:

• Assess daily glycaemic patterns

• Detect asymptomatic hypoglycaemia

• Detect persistent hyperglycaemia

• Guide adjustment of insulin and oral hypoglycaemic therapy

• Assess the effects of meals, exercise, illness, and medications

• Improve patient understanding of diabetes

• Reduce the risk of acute and chronic diabetes complications

Recommended frequency of monitoring

The frequency of SMBG should be individualized according to the patient's treatment regimen and clinical status.

Patients receiving intensive insulin therapy

Monitoring is generally recommended:

• Before each meal

• At bedtime

• Occasionally 2 hours after meals

• Before exercise

• After exercise if hypoglycaemia is suspected

• Whenever symptoms of hypo- or hyperglycaemia occur

• Before driving or operating heavy machinery if appropriate

This usually results in 3–7 measurements daily.

Patients receiving basal insulin

Monitoring is commonly recommended:

• Daily fasting blood glucose

• Additional testing when insulin doses are adjusted

• During illness or symptomatic episodes

Patients receiving oral hypoglycaemic agents

Routine SMBG may not be necessary for all patients.

Monitoring is useful:

• During treatment initiation

• During medication adjustment

• When using sulphonylureas

• During illness

• When glycaemic control deteriorates

Pregnancy

Women with diabetes during pregnancy generally require more frequent monitoring, including:

• Fasting blood glucose

• Before meals

• One or two hours after meals

• At bedtime

The frequency should be individualized according to obstetric and diabetic management.

Target blood glucose levels

General glycaemic targets for most adults are:

Targets should be individualized for elderly patients, pregnant women, children, and those at high risk of hypoglycaemia.

Procedure

Patients should be educated on the correct technique for blood glucose testing.

The procedure includes:

1. Wash and dry hands thoroughly.

2. Insert a test strip into the glucometer.

3. Use a sterile lancet to obtain a capillary blood sample from the side of the fingertip.

4. Apply the blood sample to the test strip according to the manufacturer's instructions.

5. Read and record the blood glucose result.

6. Dispose of the lancet safely in an approved sharps container.

Patients should avoid squeezing the fingertip excessively, as this may alter the result.

Interpretation of results

SMBG results should always be interpreted together with:

• Meal timing

• Medication use

• Physical activity

• Symptoms

• Recent illness

• Stress

• Alcohol intake

Persistent abnormal readings should prompt medical review and treatment adjustment.

Causes of high blood glucose readings

Common causes include:

• Missed medication or insulin doses

• Excess carbohydrate intake

• Acute illness

• Infection

• Psychological stress

• Reduced physical activity

• Inadequate insulin dosing

• Corticosteroid therapy

Causes of low blood glucose readings

Common causes include:

• Excess insulin

• Excess sulphonylurea dose

• Delayed or missed meals

• Increased physical activity

• Alcohol intake

• Vomiting or diarrhoea

• Renal impairment

Recording blood glucose

Patients should maintain a blood glucose diary documenting:

• Date

• Time of measurement

• Blood glucose result

• Meals

• Medication doses

• Physical activity

• Symptoms of hypo- or hyperglycaemia

• Any unusual events

These records assist healthcare providers in optimizing treatment.

Advantages

SMBG offers several benefits, including:

• Early detection of abnormal glucose levels

• Improved glycaemic control

• Better treatment adjustment

• Increased patient engagement

• Reduced risk of severe hypoglycaemia

• Prevention of diabetes complications

• Improved quality of life

Limitations

Potential limitations include:

• Cost of test strips and lancets

• Pain associated with finger-prick testing

• Inaccurate technique leading to erroneous results

• Poor adherence

• Limited usefulness in patients with stable diabetes managed by diet alone

• Anxiety related to frequent testing in some patients

Patient education

Patients should receive education regarding:

• Proper glucometer use

• Correct hand hygiene before testing

• Safe disposal of lancets

• Appropriate testing frequency

• Interpretation of results

• Recognition of hypo- and hyperglycaemia

• Importance of maintaining a glucose record

• Situations requiring medical attention

When to seek medical attention

Patients should seek medical review if they experience:

• Persistent fasting blood glucose above target despite treatment

• Recurrent hypoglycaemia

• Severe hypoglycaemia requiring assistance

• Persistent blood glucose greater than 15 mmol/L

• Symptoms of diabetic ketoacidosis or hyperosmolar hyperglycaemic state

• Repeated unexplained fluctuations in blood glucose

Clinical pearls

• SMBG complements but does not replace HbA1c measurement.

• Patients using insulin generally require more frequent monitoring than those managed with oral medications alone.

• SMBG results should always be interpreted in the context of meals, medications, physical activity, and clinical symptoms.

• Education on proper glucometer technique is essential to obtain accurate and reliable results.

• Maintaining a blood glucose diary improves treatment decisions and supports long-term diabetes management.