"Doctor, the blood glucose level indicated by my glucometer is quite unreliable! Should I depend on the A1c level instead?"
– Anonymous patient
A glucometer is a simple device for blood glucose testing at home. Many people find that a glucometer often gives erroneous readings. Almost every person with Diabetes would like to know how accurate is the glucometer? When and how often should people test glucose at home? In order to clarify these important issues, the cover story of this Diabetes Health issue is dedicated to demystifying the glucometer.
Any glucometer may be, occasionally, off the mark by about 9-18 per cent. It is important to confirm glucometer accuracy by a simultaneous laboratory measure of glucose. Nevertheless, the glucose meter remains useful as a rough, quick and available guide to current glucose levels. In contrast, another test called the A1c is a better measure of long term glucose control.
"The A1c is like a school teacher who always catches students talking in the class but does not notice them sleeping during a lecture".
The A1c, also called the HbA1c, tells us what proportion of hemoglobin is bound to glucose. If less than 7 per cent of your haemoglobin is bound to glucose, your doctor might say that your glucose control has been good over 3 months.
Why 3 months? That's because haemoglobin resides in red blood cells, and these cells have a life of 3 months. The A1c test is very convenient as it does not require fasting. However it has some problems. In addition to biological variations in value, as mentioned in the quote above, A1c is like the teacher who often detects hyperglycaemia (high blood glucose), but fails to point out hypoglycaemia (low blood glucose). Hypoglycaemia can be devastating, especially at night, causing coma and even convulsions. Hypoglycaemia may occur due to several anti-diabetes medications. For confirming hypoglycaemia, a glucometer is very useful as a person with Diabetes can do the test when they have early symptoms of low blood glucose like hunger, giddiness and sweating. But, what about continuous glucose monitoring (CGM)? Isn't that better than glucometer measurements?
"CGM is like a moving selfie of blood glucose".
– Yours truly
CGM is done by a small chip that can be painlessly placed under the skin and can sense glucose levels continuously: over 100 readings a day. This empowers both doctors and their patients with continuous insights into their own episodes of normal, high and low glucose. It is currently an expensive and sometimes, an approximate tool, suitable only for special cases.
A1c, Blood Glucose and CGM stand for the A, B and C of glucose measurement. All of these tests predict diabetic complications, but they are different from one another. Like the adage, "horses for courses", your doctor may choose to run the A, B or C as the appropriate test for a particular situation.
Read away to a healthy life!
Dr Unnikrishnan AG