HBA1C -what AN obstetrician NEED TO REMEMBER??

All about HBA1C :--

The relevance of Glycosylated Hemoglobin Estimation?

1)                      This kind of blood test  is useful to estimate the average control of blood glucose in the previous 90 days. 2) Unrelated to food ingestion --the blood can be drawn any time of the day. 3) Reliable Lab  is warranted: If done by a reliable laboratory it provides  important information  which  blood glucose   estimation cannot provide ideally it should be done at every three monthly follow up visit In addition to blood glucose estimation. Blood glucose(not sugar) & HBA1C are the  two values together give vital information.

For example:

1)                      Normal  HbA1c,  high FBS  :- Well the interpretation is overall control over the last 90 days was satisfactory. It is possible that either control was lost  recently or the patient  did not take the previous evening’s  medication ,. If HBA1c is normal but FBG is relatively high then consider that missed dose in previous day . This fact should be kept in mind.   Before increasing the dosage of medication under   such circumstances.

2)                       Now the reverse report:-High HbA1c  with  normal fasting  and post lunch blood  glucose :-- post prandial values need to be checked because it is easier to estimate than Post dinner B Glucose. Some people take small working  lunch but a large dinner with family members , In such men & women  their  post dinner blood  glucose values  are much higher than post lunch blood glucose values

3)                      The third  possible combination: High  HbA1c   but normal blood glucose Interpretation overall  control over th last 90 days    was poor . Whatever control is observed in FBG or PP B G is due to control of diet and more exercise was  done which has lead to achieve near normal b glucose in the last   few days. If such results are obtained in per employment check up one should suspect the possibility   of a diabetic   person hastily achieving control through   treatment   from a private  doctor so as to pass the pre employment  medical examination .

Estimation of  HbA1c has become an integral part of routine laboratory  tests in day to day management of diabetes in  economically advanced   countries  and also in any centers  in our country..

Principles  of HbA1c  test :

HbA1c  has very good co relation with  micro vascular complications  of diabetes. However  it has certain  limitations  which precludes it’s  widespread use in our  country  such as cost of estimation  and non availability  of standardizationIn circulating  blood  glucose is constantly  getting attached to hemoglobin through non enzymatic process. This attachment  is irreversible and percentage  of hemoglobin in glycated form  out of total  hemoglobin in circulation depends  upon blood  glucose level. Thus in  a diabetic  patient  depending on the degree of hyperglycemia over previous 90 days  higher percentage of hemoglobin  is glycated as  compared  to normal  percentage of hemoglobin is glycated as  compared  to normal  persons in who around  4% to 6%  of hemoglobin is glycated,. In  other words   HbA1c levels are in the range of 4% to 6% in non diabetic normal persons . Thus  a diabetic  with persistent  poor control  will have  very high  level of HbA1c  while a diabetic  with persistent  tight blood glucose  control will have his HbA1c values  near those  for normal  persons. All diabetics  should  aim to keep their HbA1c  constantly between 6.5% to 7% .

Haemoglobin A1c  as a diagnostic test for diabetes mellitus . Are we ready for it ? 

Diabetes  mellitus is a metabolic and vascular  disease  with hyperglycemia  and specific micro vascular complications in those who are poorly controlled over  a long term  period as it characteristic features . However  there is no well defined  threshold  level of blood  glucose  beyond which  micro vascular  complications develop and below which  there is a  complete immunity  from complications. Thus fating venous plasma glucose   value of 126 mg %  and tow hours post 75g  oral glucose   load   value of 200 mg%  are somewhat arbitrary diagnostic  values for diabetes  mellitus. At present   for the want   of better diagnostic  test blood glucose  values are used as the only criteria for the diagnosis of diabetes  however these  have certain  limitations.

 Among  the micro vascular  complications of diabetes diabetic retinopathy is the most extensively studied complication as regards  its co relationship  with  fasting and post  glucose   load blood glucose   values. Till 1997  fasting venous plasma  glucose and the two hours post 75 g oral glucose load cut off point  for diagnosis of diabetes were 140 mg% and 200 mg% respectively  . These points were based on symptoms  of  diabetes and not on risk for development of micro vascular  complications  Even though there  is no clear cut threshold  blood glucose value for retinopathy some people with fasting  blood glucose values  between  126-140 mg% have  evidence  of early non proliferative diabetic retinopathy however retinopathy  is very rare in those having fasting venous  plasma glucose value below 126 mg% . Thus in 1997  criteria for diagnosis  of diabetes based on fasting blood glucose were lowered  from 140 to 126  mg.  Moreover  fasting value of 126 mg% has better co  relation with post glucose  load  value of 200 mg%  as regards  micro vascular   complications  Even  though lowering  of diagnostic  fasting blood  glucose  value  was seen  as a definite  improvement  using blood glucose  values for diagnosis  of diabetes  still have some limitations such as 1)  poor reproducibility due to analytical variance 2) need to remain in fasting state  for 8hours 3)false  lower values if the blood sample is not analyzed with  in 1 hour  due to glycolysis . Laboratory methods for estimation of Haemoglobin  A1c  and instruments used for estimation  have been standardized in the advance countries by National Glycohamoglobin standardization program 99% of the laboratories estimating HbA1c  are NSGP  certified in USA.

HBA1c :--In order in express average  blood glucose  in patient  friendly and meaningful manner a large multi centric multinational work was carried out in 700 persons . 300 each had type 1 and 2 diabetes and 100 were normal controls Originally 11  centers  spread across North America Europe Africa  and Asia  were included . One centre dropped out   due to technical reasons. Those  having conditions such as anemia haemoglobinopathies and renal impairment  were  excluded from eh study  A large amount   of data on glycemic control was generated in these people by studying  was generated in these  people by studding them for 4 months  in this period   all were subjected in continuous interstitial fluid  glucose  monitoring for 48  hours every months for 4  months In addition they were subjected to HbA1c   estimation 3 times at a central laboratory in Europe Participants also  underwent self capillary glucose monitoring  seven times a day three  times a week for 4 months. From this data average  glucose value was calculated and it’s  correlation with HbA1c  was worked out and a mathematical formula to convert HbA1c  in to average glucose  value  was developed Interstitial fluid values  were scaled up by 5% to derive capillary glucose values 507  participants  completed the entire study.