HbA1c-The Reliable Diabetes monitoring parameter

Compiled by : Prateek Mittal

Embee Diagnostics Pvt. Ltd

HbA1c is a modified form of haemoglobin. Haemoglobin is the molecule in our red blood cells which carries oxygen around the body; most of the haemoglobin is of a type called HbA. A small fraction of HbA becomes modified during its lifetime (HbA1). In the late 1950s it was found that HbA1 could be separated further into HbA1a, HbA1b and HbA1c. A decade later, the clinical significance of HbA1c became apparent when it was revealed that many diabetics had uncharacteristically high levels of this haemoglobin variant.

HbA1c is formed when glucose molecules attach to HbA molecules in a process known as glycosylation. Glycosylation reactions are common and occur naturally in the body. Normally though, they take place in a controlled environment, regulated by enzymes. The process by which HbA1c is formed, however, occurs in the absence of enzymes and is therefore referred to as non-enzymatic glycosylation, or simply 'glycation'.

What controls the process then? Essentially, the reaction between glucose and protein is time and concentration dependent. This means that the amount of haemoglobin which forms HbA1c will depend on:

• The concentration of glucose that the haemoglobin is exposed to

  Not all cell types in the body require insulin for the uptake of glucose. Red blood cells have 'insulin-independent' glucose transporters on their surface. So if glucose levels in the plasma (the watery part of the blood) are high, then glucose levels inside the red blood cells will also be high. The higher the blood glucose level, therefore, the more glycosylation of haemoglobin will occur.

   

• The length of time that the haemoglobin is exposed to a given concentration of glucose

  The longer the blood glucose level is high, the more glycosylation will occur.

  Note, also, that this factor is influenced by the age of the red blood cell - many cells in our body are continually being broken down and replaced; the average life span of a red blood cell is about 120 days. The haemoglobin is continuously being glycated at a rate which is proportional to the prevailing blood glucose level. At any given time, there will be a mixture of old and new red blood cells circulating in the bloodstream. Old cells will have been exposed to recent, and not so recent, blood glucose levels. New cells will only have been exposed to recent blood glucose levels. So the more recent glycaemia will have the largest influence on the overall HbA1c reading. Indeed, it has been suggested that half of an HbA1c value is attributable to the previous month, a further quarter to the month before that, and the other quarter to the two months before that.

  Red blood cells in patients with haemolytic anemia have a short lifetime and they are therefore subject to less glycation; HbA1c levels in these people are therefore lower.

The HbA1C test is currently one of the best ways to check diabetes is under control; it is the blood test that gets sent to the laboratory, and it is done on the spot in some hospital clinics. Remember, the HbA1C is not the same as the sugar level.

Coincidentally the sugar/HbA1C numbers for good control are rather similar though: sugar levels 5.5-6.5 mmols/l half an hour before meals versus 7% HbA1C.

Below are two examples of people who have their HbA1c measured. One is poorly controlled, one well controlled.

Why should the HbA1C be measured?

Sugar levels fluctuate from minute to minute, hour to hour, and day to day. Thus for hour to hour control, or day to day, a sugar level is the best guide.
The HbA1C level changes slowly, over 10 weeks, so it can be used as a 'quality control' test.
In diabetes sugars tend to rise more than usual, dropping with exercise, rising after food, rising a lot more after sugary food, and can make it hard to control.

If your diabetes is controlled (an HbA1C lower than 7%), every 3-6 months but if the last reading is above 7% and you are in reasonable health, you will need to achieve a lower level if possible, and the next reading should be sooner. This assumes you will make changes to improve your control. There is no point in having your HbA1c measured if you are not trying to achieve good control of your diabetes, although the level does predict the likelihood of complications from your diabetes.

Here's a chart as given by HbA1c and Mean Blood Glucose comparison :

How should the HbA1C be measured?

Conventional methods including the measurement of Glycosylated Hemoglobin by Immunoturbidimetric methods are comparatively unreliable. Such tests measure HbA only and are neither accurate, nor specific markers for HbA1c. Furthermore, the presence of an abnormal Haemoglobin causes interference in the test, finally affecting the result considerably. Accurate diagnosis of HbA1c requires certain instruments. We have a wide range of instruments for testing HbA1c. 

Micromat II™ : A reliable instrument for testing HbA1c. Micromat provides on the spot and accurate results. The instrument is easy to operate and is ideal for all clinicians, diabetologists and small labs. It provides results in less than 5 minutes!!! Based on borate affinity chromatography, there is no interference from abnormal Haemoglobins and is very reliable. At Embee, we see HbA1c using Micromat as the future of diabetes testing.

Click here to know more about this instrument.

Diastat™ : This is an ideal HbA1c monitoring device for the labs and hospitals. The instrument is fast and accurate and is definitely recommended for all the Pathological Labs who wish to conduct HbA1c tests. 

Click here to know more about Diastat.

Variant™ and Variant II™ : The VARIANT™ Hemoglobin Testing System provides automated diabetes monitoring, sickle cell screening, beta-thalassemia testing and hemoglobinopathy screening. The system is a perfectly ideal solution for major labs who wish to perform a total, fast and accurate testing of these. The Variant and Variant II are both state-of-the-art systems and a must for every quality lab and hospital with considerably large work load.

Click here to know more about Variant or here for Variant II