Definition of the HbA1C test.
Table of Contents
- Definition of the HbA1C test.
- What are the indications for HbA1c tests?
- Instruction and preparation for the HbA1C test.
- Reference Value
HBA1c is a blood test used to monitor blood sugar control in persons with diabetes mellitus. Diabetes is one of the commonest chronic metabolic diseases today. The central pathophysiology of diabetes is inadequate action of the hormone insulin. This is due to a lack of production by the pancreas, the resistance of body tissue to the action of insulin or a combination of the two.
Haemoglobin, the oxygen-carrying molecule of blood, forms non-covalent bonding with glucose forming HbA1C. Its also referred to as glycated haemoglobin. This process occurs even without diabetes, however, the level of HbA1C is relatively low. As the amount of glucose rises in diabetes, HbA1c rises in tandem.
HbA1c Testing in the laboratory.
The level of HBA1c is correlated with the glucose level in the blood for a preceding period of 2-3 months. Thus, measuring HBA1c gives an indication of how well blood glucose control has been.
Levels of HBA1c are closely correlated with the risk of long-term complications of diabetes mellitus.
What are the indications for HbA1c tests?
This test is endorsed by the WHO for monitoring diabetes. So persons with the disease are advised to have their HbA1C test done at regular intervals, either 3 or 6 monthly. The WHO does not advocate using it for diagnosis, although other authorities use it for this purpose (see additional points below). However, it can be done at the time of diagnosis to give an indication of how high the sugars had been prior to the diagnosis. A level of >6.5% is in keeping with a diagnosis of diabetes.
HbA1c Testing Recommendations
- Perform the HbA1c test at least two times a year in patients who are meeting treatment goals (and who have stable glycemic control).
- Perform the HbA1c test quarterly in patients whose therapy has changed or who are not meeting glycemic goals.
- Point-of-care testing for HbA1c provides the opportunity for more timely treatment changes
Instruction and preparation for the HbA1C test.
This test doe not require any special preparation e.g. fasting, as opposed to fasting blood sugar. It’s important for the doctor to be aware of your anti-diabetic medication and dosages as this will inform subsequent management.
HbA1c Specimen Collection and Processing
Universal precautions apply. Collect whole blood specimens in vacuum collection tubes containing EDTA and mix thoroughly. The minimum volume required for analysis directly from collection tubes is 1 mL of whole blood. Whole blood samples as small as 100 uL may be run in sample cups – only for QC, patients must be in a tube.
Specimen Storage and Stability:
Blood samples for HbA1C can be stored at room temperature (5-25 °C) for up to 3 days, 17 days at 2-8 °C and 6 months if frozen at (-15) – (-25) °C
Many different systems are in use for HbA1C tests, most of which are automated.
Test Waiting time
Test results for HbA1c are usually available within 30 min- 1 hour.
The universal reference value for HbA1C is <6.5%. However, each diabetic patient should have a personalised glycemic target that’s realistic and compatible with his/her circumstances.
Additional Considerations on the HbA1c Test
- For diagnostic purposes, mmol/mol HbA1c values (IFCC) and % HbA1c values (DCCT/NGSP) should be used in conjunction with information from other diagnostic procedures and clinical evaluations.
- The test is designed only for accurate and precise measurement of mmol/mol HbA1c (IFCC) and % HbA1c (DCCT/NGSP). The individual results for total Hb and HbA1c concentration should not be reported.
- The test is not intended for the diagnosis of diabetes mellitus or for judging day-to-day glucose control and should not be used to replace daily home testing of urine or blood glucose.
- Care must be taken when interpreting any HbA1c result from patients with Hb variants. Abnormal haemoglobins might affect the half-life of the red cells or the in vivo glycation rates.
- Any cause of shortened erythrocyte survival will reduce exposure of erythrocytes to glucose with a consequent decrease in HbA1c
Causes of shortened erythrocyte lifetime include:-
- hemolytic anaemia or other hemolytic diseases
- homozygous sickle cell trait
- recent significant or chronic blood loss
- The assay does not detect glycated HbF as it does not contain the glycated Beta-chain that characterizes HbA1c. If a sample contains high amounts of HbF (> 10 %), this may result in lower-than-expected HbA1c levels
What is the cost of the HbA1C Test?
This test shows great variability in pricing across facilities and laboratories in Kenya. The price ranges from Kes 1200 to as high as 4800. Standalone laboratories, public hospitals and mission hospitals tend to charge on a lower scale, while big private hospital charge a premium. On a brighter note, most health insurance including NHIF cover the cost of the test.
Hope this article helps you understand the basics of the HbA1C test. In case of any questions don’t hesitate to contact us or comment below.
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Till next time, happy and healthy living!