Diabetes mellitus laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [2]

Overview

The diagnosis of diabetes has been done in past, based on glucose levels in plasma (fasting, post-prandial). The Expert Committee on the Diagnosis and Classification of Diabetes Mellitus (1997) had put forth diagnostic criteria based on the association between fasting plasma glucose and the presence of retinopathy. Based on the association between plasma glucose and retinopathy, the diagnostic cutpoint for diabetes was determined to be: ≥126 mg/dl (7.0 mmol/l) - Fasting glucose; 200 mg/dl (11.1 mmol/l) - Post-prandial.

Laboratory Findings

American Diabetes Association Diabetes Diagnostic Criteria (DO NOT EDIT)

Criteria for the diagnosis of diabetes

A1C ≥6.5%. The test should be performed in a laboratory using a method that is NGSP certified and standardized to the DCCT assay

or FPG ≥126 mg/dl (7.0 mmol/l). Fasting is defined as no caloric intake for at least 8 h

or 2-h plasma glucose ≥200 mg/dl (11.1 mmol/l) during an OGTT. The test should be performed as described by the World Health Organization, using a glucose load containing the equivalent of 75 g anhydrous glucose dissolved in water

or In a patient with classic symptoms of hyperglycemia or hyperglycemic crisis, a random plasma glucose ≥200 mg/dl (11.1 mmol/l)

Note that any one of the criteria above must be confirmed on a separate day (ideally with the same test) to appropriately diagnose a patient with diabetes, unless unequivocal symptoms of diabetes are present. Point of caution: Hemoglobin A1C testing is not considered sufficiently accurate to use for diagnosing diabetes.

Impaired Glucose Tests/Pre-Diabetics

The patients with impaired fasting glucose have higher risks of developing diabetes (formerly called "prediabetes"). The glucose level used to diagnose impaired glucose tests are:

• Impaired fasting glucose (IFG): FPG >100mg/dl but <126mg/dl
• Impaired glucose tolerance (IGT): Oral glucose tolerance test result at 2 hours of 140-199mg/dl
• A1C between 5.7 and 6.4%

Recent Modifications in Diabetes Diagnostic Criteria

1. Recent guidelines have been slightly modified and include HbA1C in the diagnostic criteria.

2. HbA1C provides an "integration" of plasma glucose levels over the past 2-3 months.

3. The diagnostic HbA1C cut point of is 6.5% and correlates with diabetic retinopathy complications.

4. The diagnostic test should be performed using a method that is certified by the National Glycohemoglobin Standardization Program (NGSP) and standardized or traceable to the Diabetes Control and Complications Trial reference assay.

Advantages of HbA1C

• HbA1C is more closely associated with both microvascular and macrovascular complications.
• Greater availability and standardization of the procedure to measure HbA1C has helped in its wider use.
• Physicians are familiar with the method
• Convenient for patient as no fasting required
• Minimal variability due to stress and illnesses

Disadvantages of HbA1C

• Costly
• Still not widely available in developing
• Incorrect estimates in patients with certain forms of anemia and hemoglobinopathies.
  • In patients with sickle cell anemia (abnormal hemoglobin, but normal red cell turnover) an A1C assay without interference from abnormal hemoglobin should be used
  • In patients with anemia from hemolysis and iron deficiency (abnormal red cell turnover) the diagnosis of diabetes should be done based on glucose criteria exclusively.

Other Laboratory Findings

Blood sugar | Fructosamine | Glucose tolerance test | Glycosylated hemoglobin