HbA1c is a laboratory test that shows the average level of blood glucose over the previous 3 months and how well a diabetic patient is controlling the sugars.

How is the HbA1c test carried out?

The blood specimen is obtained in two ways: either by venipuncture or fingerstick.

HbA1c may be separated by charge and size from the other hemoglobin A components in the blood by high-pressure liquid chromatography (HPLC). Here, blood is separated into its various components by adding mixtures to special liquids and then passing them under pressure through columns, which then separate it into its different component molecules.

Because HbA1c is not affected by short-term fluctuations in blood glucose concentrations.

Fasting for the blood test is not necessary.

Basic Physiology Behind The Test

Red cells have hemoglobin, which is responsible for oxygen transport. About 90% of hemoglobin is hemoglobin A, which is the adult type of hemoglobin. Hemoglobin type A is made up of 4 minor hemoglobin components. These components are slightly different chemically. They include hemoglobins A1c, A1b, A1a1, and A1a2.

Hemoglobin A1c (HbA1c) is a minor component of hemoglobin to which glucose is bound. HbA1c, also is sometimes referred to as glycated hemoglobin, is known as A1c. (C for carbohydrate), glycosylated hemoglobin, or glycohemoglobin.

When there are high levels of glucose, there is more binding of this glucose to the hemoglobin, and when measured in percentage, it is known as HbA1c or percentage HbA1c.

The hemoglobin A1c test depends on the chemical charge on the HbA1c molecule, which is different from the charges on the other three components of hemoglobin (A1b, A1a1, A1a2).

Red blood cells carry the memory of that glucose in the form of A1c. This constantly changes as the RBCs keep on changing with the new RBCs. As the lifespan of the RBCs is 3-4 months that is 120 days on average then the RBCs will carry that memory for the last 3 months.

HbA1c, therefore, helps to identify age-accelerating glycation reactions in the body.

Indications

The test is indicated for all diabetics.
It is the Gold standard test to measure glucose control for the last 3 to 4 months.
It can also be used in diabetes diagnosis.
It assesses the relative risk of diabetes.

Interpretation

Normal Results

The results of this test are expressed as a percentage of total hemoglobin, with a normal result being 4% to 7% (SI, 0.04 to 0.07) or less than or equal to 5.6% (SI, 39 mmol/mol)

Abnormal Results

An Hb A1c level greater than 6% (or blood glucose level of 126 mg/dL [SI 7.0 mmol/L]) indicates an increased risk of developing diabetes
An Hb A1c level of 5.7% to 6.4% (SI, 30 to 37 mmol/mol) is considered the prediabetic range.
In a patient with diabetes, an Hb A1c level of 7% or higher (blood glucose 170 mg/dL [SI, 9.3 mmol/L] or higher) indicates that diabetes isn't well controlled. The patient may need to undergo a repeat test to confirm the results. Note that each patient's target Hb A1c level is individually determined by the patient and practitioner.
A patient with a low hemoglobin level may have a falsely low Hb A1c level.
A patient with iron deficiency may have a falsely high Hb A1c level.

Fasting plasma glucose or random blood glucose just gives a snapshot and does not tell you about your overall diabetic state. Therefore, it will not measure the severity or control of diabetes.

For any non-diabetic individual, the goal is to maintain HbA1c levels close to or even less than 5%.
In diabetic patients, the goal is to keep the levels below 7%.

The test may be incorrect in patients with

Anemia
Kidney disease
chronic excessive alcohol intake,
Hypertriglyceridemia.
Vitamin C and E can cause a falsely low HbA1C level because of there inhibition of the glucose and hemoglobin binding.

Medical conditions that may falsely decrease HbA1c include

Acute or chronic blood loss,
Sickle cell disease,
Thalassemia.

When there are high HbA1C levels, They mean that one is at risk of developing

Eye disease-retinopathy.
Heart disease.
Kidney disease-nephropathy.
Nerve damage-neuropathy.
Stroke-CVA.

Purpose of the test

To determine whether a patient has diabetes
To determine whether a patient with diabetes is managing it successfully,

Preparation

Note that the patient does not need to fast before the test.
Notify the laboratory and practitioner of all medications that the patient is taking because some medications can affect the test results, requiring the patient to hold them before the test.

Teaching Points

Be sure to include the patient's family or caregiver in your teaching, when appropriate.

Explain that the test determines average blood glucose levels over the past 2 to 3 months to help diagnose diabetes or evaluate diabetes management.
Inform the patient who will perform the test and where it will take place.
Explain that the patient need not restrict food or fluids before the test.
Tell the patient that the test requires a blood sample from a vein, which may cause slight discomfort from the tourniquet and needle puncture.
Inform the patient that the test should take less than 5 minutes.
Explain to a patient with diabetes that measurement of glycosylated hemoglobin A1c (Hb A1c) level does not replace daily glucose monitoring.

Diagnostic Procedure

Key Steps

Perform hand hygiene.
Put on gloves.
Confirm the patient's identity using at least two specific and unique patient identifiers.
Perform a venipuncture.
Collect a blood sample in a 5-mL purple-topped tube.
Note on the laboratory request the time that you collected the sample, label the tube with the patient's identification, and then immediately send the sample to the laboratory.