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How is HbA1c testing used to detect diabetes?

How is HbA1c testing used to detect diabetes?

Diabetes is one of the fastest growing health problems in western societies and it’s estimated that there are currently more than 3.5 million people living with the condition in the UK.

Modern medicine means that the condition can be mostly managed, with most sufferers living long and relatively unhindered lives.

However, it is also a condition that often goes undiagnosed and the later that diabetes is found, the more dangerous it is to the patient. This means that accurate testing is a vital defence against this growing threat.

How HbA1c testing can help

Various tests for diabetes have been available for decades, but have suffered from problems which meant diagnosis wasn’t always accurate. However, a more modern test is now available which solves the biggest problems of previous methods. This test is known as the HbA1c test, also referred to as a1c testing or glycol haemoglobin testing. It has been recommended for use in the diagnosis of type 2 diabetes and – crucially – the condition of prediabetes since 2009.

HbA1c is the shorthand term for glycated haemoglobin, a substance formed in human blood when red blood cells (haemoglobin) become attached to molecules of blood sugar (glucose). This formation of glycated haemoglobin is a natural process which depends on the levels of glucose in the blood – the higher the glucose level, the more red blood cells become glycated. HbA1c is, therefore, a proxy measurement for blood sugar level, with obvious implications for detecting diabetes.

However, the crucial point is that once haemoglobin becomes glycated, it stays that way until the cell dies naturally, which typically takes between eight and twelve weeks. This has the effect of providing an indirect measurement of historical blood sugar levels over roughly a 3 month period, as peaks and troughs of glycation will tend to smooth out the aggregate HbA1c count over time.

Why is this important for diabetes diagnosis?

Measuring the level of HbA1c in the blood effectively provides a 3 month average of blood sugar levels, and is expressed as a percentage. The average person has an HbA1c count of less than 6%. Someone with type 2 diabetes has a score of 6.5% or higher. This leaves a gap between 6% and 6.5%, where the patient is said to have prediabetes.

Prediabetes is a risk factor for type 2 diabetes rather than a waypoint on its development. A person with prediabetes will not necessarily go on to develop full diabetes and does not require treatment in the meantime. However, the increased risk means that further tests at annual intervals are recommended to detect full diabetes as early as possible, should it develop.

Why HbA1c is better than traditional testing

This ability of HbA1c testing to detect the pre-diabetes condition is one of its great strengths. Previous tests only identified full diabetes, either because of limitations in the techniques used or because they were rarely used unless there was already a strong suspicion, their result would be a definite diagnosis of type 2 diabetes.

HbA1c testing is also more accurate than older testing methods. The measurement is thought to be accurate within half a percentage point of the result, meaning that only borderline cases are likely to be misdiagnosed. In these cases, the second test at a later date will almost always provide a firm diabetes diagnosis or rule it out.

Lastly, HbA1c testing is far more convenient. Previous test methods which measured blood sugar levels directly could be heavily influenced by modern diet, stress levels, fatigue, alcohol consumption and the taking of medication. This inaccuracy meant that either multiple tests were needed for a firm diagnosis, or that the test required to be viewed in combination with other symptoms – which of course, do not tend to show up until diabetes is well established.

The smoothing effect of HbA1c means that a single test is far more reliable, and it’s a simple procedure. A preliminary analysis can be carried out during a routine health care visit, as part of a general test whether the doctor suspects diabetes or not. It is hoped that this convenience and reliability will detect far more people with prediabetes or the early stages of diabetes so that treatment can be given.

Is HbA1c testing perfect?

Unfortunately, nothing in life is perfect and HbA1c testing also has a few drawbacks to go with its certain advantages. Firstly, there is the previously mentioned margin of error which can make diagnosis difficult in borderline cases. However, the margin involved is far smaller than with older testing methods.

Secondly, some people naturally have a slightly different type of haemoglobin, known as a variant, which can interfere with HbA1c test results. This variant haemoglobin is most often found in people of African, Mediterranean, or SE Asian descent or in people with sickle cell anaemia, thalassemia or some other blood disorders. In these cases, HbA1c testing cannot be definitively relied upon and subsequent testing using old methods should be used to confirm the results.

Lastly, some underlying health problems can interfere with the normal production of glycated haemoglobin, rendering the HbA1c test unreliable. These conditions include relatively minor problems such as iron deficiency or far more serious ones including reduced kidney function and liver disease.

Nonetheless, despite these drawbacks, HbA1c testing is a giant stride forward in the detection of type 2 diabetes – and just as importantly, the previously under-diagnosed condition of prediabetes.


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