How to Check Blood Sugar at Home and Avoid Common Errors

What a Home Meter Can and Cannot Tell You

A home glucose meter measures the sugar level in a small drop of blood from the fingertip at one moment in time. Repeated readings, taken at planned times, show patterns — for example, whether levels are higher after certain meals, lower at night or changing after a medicine adjustment.

Home meters are designed for monitoring, not for diagnosing diabetes. Their results can differ somewhat from a laboratory test on a vein sample, and this is expected. If a meter reading seems very different from how the person feels, or from recent laboratory results, repeat the test carefully and discuss it with the doctor.

Before You Test

• Wash hands with soap and warm water, then dry them completely. This is the single most important step. Fruit juice, sweets or even handling food can leave sugar on the skin and produce a falsely high reading. Water left on the finger can dilute the drop.
• Check the test strips. Strips past their expiry date, or strips that have been left in heat, humidity or sunlight, may give inaccurate results. Keep the container closed and store it as the manufacturer directs — avoid leaving it in a vehicle or near a window.
• Use the correct strips for the meter. Some meters need to be coded or set up for a new batch of strips; follow the instructions for your model.
• Have the logbook ready so the result can be written down straight away.

Step by Step: Doing the Test

1. Insert a new strip into the meter as instructed.
2. Use the side of a fingertip rather than the pad, which is more sensitive. Rotate fingers from test to test to avoid sore spots.
3. Use a new lancet if possible. Re-using lancets makes them blunt and more painful, and increases infection risk.
4. Allow a drop of blood to form. If needed, hang the hand down or gently massage from the base of the finger towards the tip. Avoid squeezing hard at the fingertip, which can dilute the sample with tissue fluid.
5. Touch the drop to the strip and wait for the result. Do not smear blood onto the strip or add a second drop unless the meter instructions allow it.
6. Record the result, dispose of the lancet safely in a rigid container, and do not share lancing devices between people.

Common Errors That Affect Readings

• Testing without washing hands, especially after preparing or eating fruit.
• Using an alcohol swab and testing before the skin has dried.
• Expired or poorly stored strips, or strips from a different meter brand.
• Too small a drop of blood, or squeezing the finger forcefully.
• Very cold hands, dehydration or poor circulation, which can make fingertip readings less reliable.
• Writing results down later from memory, or recording only "good" readings.

When to Test and How to Record Results

How often and when to test depends on the type of diabetes, the medicines used and the reason for monitoring. People taking insulin usually need more frequent testing than those managed with diet or some tablets. Your doctor or diabetes team should tell you which times are useful — for example before breakfast, before other meals, two hours after a meal or at bedtime.

A useful record includes the date, time, the reading, whether it was before or after a meal, and any medicine taken. Note anything unusual, such as illness, a missed meal, unusual exercise or a missed dose. Bring the logbook or meter to appointments and to a doctor home visit.

Target ranges differ between people. An older person at risk of falls, a pregnant woman and a young adult may all have different targets. Rather than relying on general figures, ask your doctor to write down the range that applies to you and the readings that should prompt a call.

Low Blood Sugar (Hypoglycaemia)

People taking insulin or certain diabetes tablets can develop low blood sugar. Symptoms may include shaking, sweating, hunger, a fast heartbeat, irritability, confusion or unusual behaviour. Older people may show mainly confusion, drowsiness or unsteadiness, and some people have few warning symptoms.

If a person with diabetes has symptoms like these, check the blood sugar if it can be done quickly. If they are awake and able to swallow safely, follow the low-sugar plan given by their doctor, which usually involves a fast-acting sugar source followed by a recheck. Tell the doctor about any episode of low blood sugar, because medicines may need to be reviewed.

Readings During Illness

Infections, vomiting, not eating and dehydration can all change blood sugar levels, sometimes quickly. During illness, more frequent testing may be needed, and some medicines may need temporary adjustment. This should be done according to advice from your doctor rather than guesswork. If you are unable to eat or drink normally, contact your doctor early.

Related Guides

• How to Measure Blood Pressure Correctly at Home
• Fasting Blood Tests: Which Tests Actually Require Fasting?
• Preventing Dehydration in Older Adults
• When Home Care Is Not Enough: Signs You Should Go to Hospital