For many years the diagnosis of diabetes mellitus was based on the fasting and two-hour post meals blood glucose levels.
In 1997 data was examined and the level of blood sugars at which there was a very low prevalence of diabetic retinopathy (eye changes in diabetes) was established.
These data confirmed the 200 mg/dl cut off point two hours postprandial as one of the diagnostic criteria for diabetes but the cut off for fasting blood glucose was lowered from 140 mg/dl to 126 mg/dl.
The prevalence of retinopathy (eye changes in diabetes) at blood sugar levels defined by fasting and postprandial levels were similar to glycated hemoglobin levels of greater than 6.4%. Because of the laboratory standardization, it was not approved until recently as a diagnostic tool.
Similarly, patients who had a random plasma glucose of more than 200 mg/dl along with the classical symptoms of hyperglycemia were also included.
|Criteria for the diagnosis of diabetes mellitus|
|1.||Fasting plasma glucose of 126 mg/dl or more. Fasting is defined as no caloric intake for eight hours.|
|2.||Two – hour plasma glucose of more than 200 mg/dl during an oral glucose tolerance test.|
|3.||Glycated hemoglobin (HbA1C) of more than 6.4%|
|4.||Random blood glucose of more than 200 mg/dl in a patient with classical symptoms of hyperglycemia (increased urination, increased thirst, increased appetite)or hyperglycemic crisis.|
|In the absence of unequivocal hyperglycemia; criteria 1 – 3 should be confirmed by repeat testing|
Diabetes Diagnosis – the role of Glycated hemoglobin (HbA1C or A1C):
Glycated hemoglobin is widely used as a marker of glycemic status over the past three months. It has been approved as a diagnostic tool in patients with diabetes mellitus. Its greatest use is to monitor the diabetic status of the patient and adjust antidiabetic medications accordingly.
Glycated hemoglobin levels cannot be reliably used to deduce either mean fasting or mean postprandial glucose values of a patient. But since A1C correlates well with both microvascular and to some extent macrovascular complications, it is widely used for the adequacy of diabetic control.
Apart from its association with complications, it is also convenient for the patients since fasting is not required and there is less day to day variations during stress or illnesses.
These advantages must be balanced by limited availability, greater cost and falsely high or low results in certain conditions, especially in anemias, hemoglobinopathies, and polycythemia. It is also important not to use it in certain types of diabetes especially those with rapid onset and gestational diabetes.
Screening for Diabetes Mellitus:
In diabetes, screening plays a very important role to diagnose the patient at an earlier age. Screening healthy subjects may lead to early diagnosis.
Initiation of early treatment prevents the patient from complications and diabetes-associated complications. Unlike patients with ischemic heart disease and many other diseases, patients with diabetes are usually asymptomatic.
Patients thus present years after the disease onset. Most of these patients present with either non-specific symptoms or present to the hospital because of some other illness and are found to have diabetes.
The American Diabetes Association recommends screening of all individuals above 45 years of age at 3 yearly intervals.
Patients who are at increased risk should be screened earlier.
In a systematic review of 44,203 individuals, those with glycated hemoglobin between 5.5 and 6.0% had a substantially increased risk of diabetes.
The 5-year incidence of diabetes ranged from 9 to 25%. A glycated hemoglobin range of 6.0–6.5% had a 5-year risk of developing diabetes between 25 and 50%.
Who are at risk of developing type 2 Diabetes Mellitus:
- A family history of diabetes (i.e., parent or sibling with type 2 diabetes)
- Obesity (Body Mass Index ³25 kg/m2)
- Physical inactivity
- Race/ethnicity (e.g., African American, Latino, Native American, Asian American, Pacific Islander)
- Previously identified with impaired fasting glucose, impaired glucose tolerance, or glycated hemoglobin of 5.7–6.4%
- History of gestational diabetes mellitus (diabetes in pregnancy) or delivery of baby >4 kg (9 pounds)
- Hypertension (blood pressure ³140/90 mmHg)
- High density lipoprotein cholesterol level <35 mg/dL (0.90 mmol/L) and/or a triglyceride level >250 mg/dL (2.82 mmol/L)
- Polycystic ovary syndrome or acanthosis nigricans
- History of cardiovascular disease.
Gestational Diabetes Mellitus:
Gestational Diabetes Mellitus carries risk to both the mother and the child.
Diagnostic cutoffs were defined for fasting, one hour and two hours plasma glucose based on the odds ratio of adverse outcomes of at least 1.75 times.
It is now recommended that all pregnant women not known to have diabetes should undergo a 75 gm oral glucose tolerance test at 24 to 28 weeks of gestation.
The screening and diagnosis of GDM are summarized in the following table:
One step approach (IADPSG consensus):
Perform a 75 gm OGTT after an overnight fast of at least 8 hours. GDM is diagnosed when any of the following values are exceeded:
- Fasting: 92 mg/dL (5.1 mmol/L)
- 1 hour: 180 mg/dL (10.0 mmol/L)
- 2 hour: 153 mg/dL (8.5 mmol/L)
2. Two-step approach (NIH consensus):
Perform a 50-g Glucose tolerance test (nonfasting), if plasma glucose ³ 140 mg/dl proceed to 100-g oral glucose tolerance test (Step 2 – after an overnight fast). Diagnosis of gestational diabetes mellitus is made when any two values are exceeded
Carpenter/Coustan or NDDG
Fasting 95 mg/dL 105 mg/dL
1 h 180 mg/dL 190 mg/dL
2 h 155 mg/dL 165 mg/dL
3 h 140 mg/dL 145 mg/dL
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