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  • Writer's pictureDr. Karuturi Subrahmanyam

Difference between Glucometer and Lab test Glucose (Sugar) Readings


If you have diabetes, you need to check your blood glucose (sugar) levels regularly to monitor your condition and manage it better. There are two common ways to check your blood glucose levels: using a glucometer at home or getting a lab test at a clinic or hospital. But what is the difference between these two methods and which one is more reliable? Let’s find out.

What is a glucometer?

A glucometer is a small device that measures the amount of glucose in your blood using a drop of blood from your finger. You can use a glucometer at home or anywhere else to check your blood glucose levels at any time of the day. A glucometer consists of:

  • A meter that displays the result

  • A test strip that reacts with the blood sample

  • A lancet that pricks your finger to get the blood sample

  • A lancing device that holds the lancet and makes the prick easier and less painful

To use a glucometer, you need to insert a new test strip into the meter, prick your finger with the lancet, and touch the edge of the test strip to the drop of blood. The meter will then show your blood glucose level in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L).

What is a lab test?

A lab test is a more accurate and reliable way to measure your blood glucose level. A lab test involves taking a sample of your blood from a vein in your arm and sending it to a laboratory for analysis. A lab test can measure different types of blood glucose levels, such as:

  • Fasting blood glucose, which is the level of glucose in your blood after not eating or drinking anything except water for at least eight hours

  • Postprandial blood glucose, which is the level of glucose in your blood after eating a meal

  • Random blood glucose, which is the level of glucose in your blood at any time of the day regardless of when you ate last

  • Hemoglobin A1c (HbA1c), which is the average level of glucose in your blood over the past two to three months

A lab test can also measure other factors that affect your blood glucose levels, such as insulin, ketones, cholesterol, and triglycerides.

What is the difference between glucometer and lab test results?

The main difference between glucometer and lab test results is the accuracy of the results. Glucometers are less accurate than lab tests, and the results can vary depending on several factors, such as:

  • The quality and calibration of the device

  • The technique and timing of obtaining the blood sample

  • The storage and handling of the test strips

  • The environmental conditions, such as temperature and humidity

  • The individual variation in blood composition, such as hematocrit (the proportion of red blood cells)

Another difference between glucometer and lab test results is the source and type of blood sample. Glucometers use capillary blood, which is the blood from the small vessels in your finger. Lab tests use venous blood, which is the blood from the large vessels in your arm. Capillary blood contains more glucose than venous blood because it reflects the recent changes in glucose intake and metabolism. Venous blood contains less glucose than capillary blood because it reflects the average glucose level over a longer period of time.

Moreover, glucometers measure whole blood glucose, which is the amount of glucose in both plasma (the liquid part of blood) and red blood cells. Lab tests measure plasma glucose, which is the amount of glucose only in plasma. Whole blood glucose is lower than plasma glucose because red blood cells contain less water than plasma.

How much difference between glucometer and lab test results?

The difference between glucometer and lab test results can vary depending on several factors mentioned above. Generally, glucometer readings are considered acceptable if they are within 15% to 20% of lab test results. For example, if your lab test result is 100 mg/dL, your glucometer result should be between 80 to 120 mg/dL.

However, some studies have shown that some glucometers may have larger errors than others, especially at high or low glucose levels. Therefore, it is important to compare your glucometer results with lab test results periodically to check their accuracy and consistency.

You can do this by:

  • Taking your glucometer with you when you go for a lab test

  • Giving a blood sample for the lab test from your arm

  • Checking your blood glucose with your glucometer from your finger immediately after giving the sample

  • Comparing the results and noting the difference

  • Repeating this process at different times of the day and under different conditions

If your glucometer results are within 15% to 20% of your lab test results, you can trust your glucometer and use it for regular monitoring of your blood glucose levels. If your glucometer results are more than 15% to 20% different from your lab test results, you may need to:

  • Check the quality and calibration of your device

  • Follow the instructions and precautions for using your device correctly

  • Replace your device or test strips if they are expired or damaged

  • Consult your doctor or pharmacist for advice

Difference between Glucometer and Lab test Glucose (Sugar) Readings: Summary

Glucometer and lab test are two common ways to check your blood glucose levels. Glucometer is a convenient and quick way to check your blood glucose levels at home or anywhere else. Lab test is a more accurate and reliable way to check your blood glucose levels at a clinic or hospital.

The main difference between glucometer and lab test results is the accuracy of the results. Glucometer results are less accurate than lab test results, and they can vary depending on several factors. Lab test results are more accurate than glucometer results, and they can measure different types of blood glucose levels.

The difference between glucometer and lab test results can vary depending on several factors. Generally, glucometer readings are considered acceptable if they are within 15% to 20% of lab test results. However, some glucometers may have larger errors than others, especially at high or low glucose levels.

Therefore, it is important to compare your glucometer results with lab test results periodically to check their accuracy and consistency. You can do this by taking your glucometer with you when you go for a lab test, giving a blood sample for the lab test from your arm, checking your blood glucose with your glucometer from your finger immediately after giving the sample, comparing the results and noting the difference, and repeating this process at different times of the day and under different conditions.

If your glucometer results are within 15% to 20% of your lab test results, you can trust your glucometer and use it for regular monitoring of your blood glucose levels. If your glucometer results are more than 15% to 20% different from your lab test results, you may need to check the quality and calibration of your device, follow the instructions and precautions for using your device correctly, replace your device or test strips if they are expired or damaged, or consult your doctor for advice.


Dr. Karuturi Subrahmanyam, MD, FRCP (London), FACP (USA)

Internal Medicine Specialist


Kify Hospital

Danavaipeta

Rajahmundry

Phone : 85000 23456

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