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Diabetes: Reading A Glucometer

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What is a glucometer?

A glucometer is a portable medical device which can be used by diabetics for home blood glucose monitoring (HBGM). 

The table below offers a comparison between the 2 main types of glucometers which are available commercially – Self-monitoring Blood Glucose (SMBG) systems and Continuous Glucose Monitor (CGM) systems.

Comparison of features of SMBG vs CGM

Self-monitoring Blood Glucose (SMBG) Systems Continuous Glucose Monitor (CGM) Systems
  • Require finger pricks for capillary blood sampling with each measurement
    •  E.g. Accu-Chek
  • Single needle stick to insert sensor under skin, thereafter obviates the need for finger pricks for measurement
    • E.g. FreeStyle Libre
  • Provides only snapshots of blood glucose concentration, limited by the number of finger-sticks a patient is willing to perform per day
  • Monitors blood glucose concentration almost continuously (every 5 mins, ~ 288 readings daily) and can help to identify trends in glucose control
  • More accurate measurement of true blood glucose; provide results that are within ±15% of a laboratory standard for concentrations >100 mg/dL or within ±15 mg/dL for concentrations <100 mg/dL, ≥95% of the time.
  • Not as accurate because they read the glucose levels in the interstitial fluid which lags behind the levels in the blood
  • Relatively affordable
  • More expensive (~≥2x)
  • Useful features like memory storage (e.g. 50 to 500 readings), average of glucose readings (e.g. 7-day or 30-day averages), customisable alarms
  • More sophisticated data management:
    • Data can be shared with multiple followers – family members, healthcare providers
    • Glucose levels can be predicted and user alerted way before glucose excursions for prompt action to be taken, especially useful for asymptomatic hypoglycaemia
    • Some can work in tandem with an insulin pump, calculate a precise bolus dose of insulin with meals.
  • Some glucometers require manual calibration with each new batch of test strips used; others may be automatically coded.
  • Some may still need calibration with SMBG

When choosing a glucometer for home blood glucose monitoring, some considerations include ease of use, blood sample volume requirement, affordability and special features e.g. reminder alarms, audio capability for those with visual impairment, memory storage.

How to use a glucometer?

As SMBG systems are more commonly used than CGM systems, the steps below are a guide on how to operate SMBG systems.

  • Insert a test strip into your meter.
  • Use your lancing device on the side of your fingertip to get a drop of blood.
    • With some meters, you can also use your forearm, thigh, or fleshy part of your hand.
    • Most lancets allow the user to set how deep they penetrate skin. People with thicker drier skin should set penetration higher.
  • Touch and hold the edge of the test strip to the drop of blood and wait for the result.
  • Your blood glucose level will appear on the meter’s display in units of mg/dL or mmol/L.

It is important to note that all meters are slightly different, so always refer to the user’s manual for specific instructions.

How to ensure accurate blood glucose readings

Certain factors may affect accuracy of SMBG readings, and it is important to observe the following to ensure validity of results:

1) Wash and dry your hands thoroughly before pricking your skin.

  • Contamination of the fingers with food residue will impact blood glucose levels. For example, just touching a banana or cutting a piece of fruit can send your numbers sky high. 
  • If your finger is wet, the blood sample may be diluted, and reading may be falsely low.

2) Store glucometer and test strips in a cool, dry place at room temperature

  • Test strips should be stored in their original container.

3) Use appropriate test strips.

  • Do not use expired test strips; check the manufacturer’s recommendation on shelf life of test strips after opening.
  • Use only strips that are meant for your specific glucometer.

4) Ensure proper coding of meter.

  • Some meters must be coded to each container of test strips. Be sure the code number in the device matches the code number on the test strip container.

5) Repeat testing on fingertip if you have reason to suspect inaccurate reading from another test site.

  • Due to the physiological differences in blood circulation at various parts of your body, blood samples from alternate sites are not as accurate as fingertip samples when your blood sugar level is rising or falling quickly. 
  • If you are using a site other than your fingertip and you think the reading is wrong, test again using blood from a fingertip.

6) Ensure adequate blood is applied to the test strip. 

  • You can increase blood flow by washing your hands with warm water prior to testing.
  • If you still have insufficient blood, squeeze your finger beginning at the part closest to your palm, and work your way down your finger until you have enough.

7) Match your glucometer reading with lab results. 

  • Take the glucometer along when you visit your doctor or have an appointment for bloods. 
  • Check your blood sugar level with your glucometer at the same time that blood is drawn for lab tests. Then compare your meter’s reading with the lab results. Results that are within 15% of the lab reading are considered accurate.
  • If your meter is not functioning properly, contact the manufacturer for advice, repair or replacement.

Interpreting Blood Glucose Levels

Targets for blood glucose levels:

  • Blood glucose before meals – 4.0 to 7.0 mmol/L
  • Blood glucose 2 hours after meals – Below 10 mmol/L

Targets may vary from person to person depending on individual’s age, weight and co-morbidities (other medical conditions). It is useful to keep a record or log of food eaten and correlate with blood glucose readings. It may also enable your healthcare provider to better adjust your medications as necessary.

Besides high blood glucose readings, diabetics should be mindful of excessively low blood glucose readings i.e. hypoglycaemia, defined as blood glucose <70 mg/dL (3.9 mmol/L). The symptoms include tremor, palpitations, sweating, hunger, dizziness, weakness, drowsiness, confusion, and at critically low levels, may result in seizure, coma or death. 

In the event of hypoglycaemia as confirmed with glucometer, the user should consume 15 to 20 grams of sugary food (e.g. glucose tablets, candy) or beverage (soft drinks, honey, fruit juice) and recheck blood sugar levels 15 minutes after. Repeat until blood sugar is above 70 mg/dL (3.9 mmol/L).

How often should you check your Blood glucose?

  • Type 1 diabetes – 3 or more times daily
  • Type 2 diabetes
    • Insulin treated – 2 to 3 times a day, on 2 to 3 days a week
    • Non-insulin treated – Sufficient to facilitate reaching glucose targets

Why is measuring your blood glucose important?

Diabetes, if untreated, can potentially lead to serious complications e.g. kidney damage, nerve damage, heart disease or stroke. However, lifestyle changes and medications can be effectively manage it. Regularly testing your blood glucose helps measure the effectiveness of your dietary modifications, physical activity and medications. 

Self-monitoring can also alert you to blood glucose levels that are deranged, which requires prompt treatment. For example, readings that are high may prompt you to adjust your insulin dose (as per doctor’s instructions), whereas readings that are low may prompt you to eat a snack.

HBGM will facilitate achievement of good blood sugar control and maintenance within safe limits.

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