Glycosylated Haemoglobin: An indicator of Diabetes mellitus

In this blog, I would like to post a very common complication involved in Diabetes mellitus (particularly Type I Diabetes),i.e.- Glycosylated Haemoglobin.

Glycosylated (or glycated) haemoglobin is a form of haemoglobin used primarily to identify the average plasma glucose concentration over prolonged periods of time. Its name is sometimes abbreviated as HbA1C. It is formed in a non-enzymatic pathway when hemoglobin remains exposed to high plasma levels of glucose (more than physiological glucose level in blood). Glycosylation of hemoglobin has been implicated in nephropathy, retinopathy, microangiopathy and consequently neuropathy in diabetes mellitus. Monitoring the HbA1c in diabetic patients may improve treatment.

The normal life span of haemoglobin is 120 days.Also, the gIycosylation of haemoglobin is a very slow process.It takes normallyl 120 days to complete gycosylation of a single haemoglobin molecule.In individuals with poorly controlled diabetes, increase in the quantities of these glycated haemoglobin is noted.

Once a hemoglobin molecule is glycated, it remains that way. A buildup of glycated hemoglobin within the red cell reflects the average level of glucose to which the cell has been exposed during its life cycle. Measuring glycated hemoglobin assesses effectiveness of therapy by monitoring long-term serum glucose regulation.

In general, the normal range of glycosylated haemoglobin found in healthy persons is quite low,just about 4%–5.9%.
Higher level of glycosylated haemoglobin is found in people with persistently elevated blood sugar, as in diabetes mellitus, particularly type I diabetes. A diabetic person with good glucose control has a HbA1c level that is close to or within the reference range. Persistent elevations in blood sugar (and therefore HbA1c) increase the risk for the long-term vascular complications of diabetes such as coronary disease, heart attack, stroke, heart failure, kidney failure, microangiopathy, neuropathy and demyelination of axons, blindness, loss of sensation, especially in the feet, gangrene etc. Poor blood glucose control also increases the risk of short-term complications of surgery such as poor wound healing.

The microangiopathy caused may also decrease immunocompetency of the patient rendering him more susceptible to secondary infections.

Lower than expected levels of glycosylated haemoglobin can be seen in people with shortened red blood cell life span, such as with glucose-6-phosphate dehydrogenase deficiency, sickle-cell disease, or any other condition causing premature red blood cell death. Conversely, higher than expected levels can be seen in people with a longer red blood cell life span, such as with Vitamin B12 or folate deficiency (since, these are maturation factors and render the presence of comparitively long living precursor cells of RBC).

Glycosylated hemoglobin is recommended for both:

(a) checking blood sugar control in people who might be pre-diabetic
(b) monitoring blood sugar control in patients with more elevated levels (diabetes mellitus).

Few very beautiful sites that may be referred for more information on this topic are enlisted below:

a) http://medweb.bham.ac.uk/easdec/prevention/what_is_the_hba1c.htm#diagram
b) http://www.doctorndtv.com/topics/detailtopics.asp?id=72
c) http://www.rssdi.org/1985_july-sept/free_paper3.pdf
d) http://www.mydr.com.au/default.asp?article=2458
e) http://www.officialdiabetesblog.com/2007/03/01/the-hba1c-%E2%80%A6%E2%80...