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What Does an HbA1c Blood Test Measure?

What does an HbA1c blood test measure?

HbA1c is a form of haemoglobin and is also known as haemoglobin A1C, glycated haemoglobin or just A1C.

Haemoglobin is the protein within red blood cells that circulates oxygen from our lungs to the rest of our bodies. The name is derived from the Greek word for blood and the Latin word for ball. Glycated haemoglobin differs from other types by being bonded to a blood sugar like lactose, fructose or glucose. The latter  is a fundamental fuel for human metabolism. All three are monosaccharides: the chemically simplest form of sugar.

What is HbA1c?

This chemical bonding between haemoglobin and sugars – glycation – occurs spontaneously when blood sugar reaches a certain level. Therefore HbA1c can indicate high levels of blood sugar: a key symptom of diabetes

Diabetes is an increasingly common disorder, which affects the ability of the body to properly metabolise glucose, causing this substance to accumulate in the bloodstream, with potentially very serious effects on health. The multiple risks of diabetes include heart disease, kidney disease, nerve damage, eye damage and hearing impairment.

Glucose metabolism is regulated by the hormone insulin. It occurs in two forms:

  1. Type 1 diabetes: this will develop if the pancreas fails to produce sufficient insulin. This is the more severe form and is often lifelong, typically developing in childhood.
  2. Type 2 diabetes: this usually develops more gradually over time, usually in later life as a result of an unhealthy diet containing too much sugar. The body slowly becomes less responsive to insulin, and as this insulin resistance develops, glucose metabolism begins to deteriorate. This is called prediabetes. If left untreated, prediabetes will turn into type 2 diabetes

What is an HbA1c test and what does it test for?

An HbA1c blood test is designed to assess the quantities of glycated haemoglobin in your bloodstream over a period of time in order to develop as full a picture as possible of your average blood glucose levels.

It is important to be tested at least once a year if you are at risk: but it is better still to be tested every few months, especially if doctors have already established that your HbA1c is higher than it should be. This is because blood cells only circulate through our bodies for around three months before being replaced by fresh, unglycated cells. Therefore any reading can only reflect blood glucose levels for the previous twelve weeks or so.

How does the test work?

A blood sample – normally taken from the patient’s arm – is despatched for analysis in a clinical laboratory. Testing equipment will assess the amount of glycated haemoglobin present. It is not a difficult substance to detect and the amount of blood taken for the sample may be quite small. No more than a few droplets is normally required from children.

Limitations of HbA1c tests

Like most testing procedures, HbA1c tests are not flawless and cannot offer 100% accuracy. There are a number of potentially complicating factors:

  • A spike in blood sugar levels in the run-up to the test can overshadow levels in the proceeding weeks, distorting the assessment. Some illnesses can cause a temporary jump in blood sugar levels.
  • Pregnancy may lead to inaccurate glycated haemoglobin readings
  • Anaemic patients often have abnormally low haemoglobin levels, preventing accurate test results.

Benefits of HbA1c tests

HbA1c blood tests enable accurate diagnoses of both type 1 and type 2 diabetes, as well as prediabetes. They also allow those who have already been diagnosed to proactively manage their health and avoid diabetic complications. 

If you suspect that you may be at risk of developing type 2 diabetes you should certainly speak to your doctor, who will refer you for testing. But if waiting times are lengthy, why not get a head start with a home-administered HbA1c blood test? The results will lay out your personal level of risk and allow you to proactively modify your diet to reduce your chances of developing the condition.

Understanding your test results

Your HbA1c test results will be listed in the international standard measurement mmol/mol or millimoles per mol. The mole or mol is an internationally recognised chemical unit, used to measure the amount of a substance present. The mmol/mol metric is defined by the International Federation of Clinical Chemistry (IFFC).

Even slightly elevated levels of glycated haemoglobin increase your risk of developing diabetes and the associated complications. According to the National Institute for Health and Care Excellence (NICE), a patient who has already developed diabetes should be looking to maintain an HbA1c level of 48 mmol/mol or less. Meanwhile, an ideal level for a person in a state of prediabetes is 42mmol/mol or lower.

It is helpful to track your results over time and correlate these with events in your life for added context. Lifestyle changes, medication, illness and stress can all affect the results.

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