Diabetes diagnosis and screening are two different entities. Diagnosis is usually undertaken when an individual exhibits symptoms or signs of the disease. The purpose of screening is to identify high risk and non-symptomatic individuals who are likely to have diabetes. Separate diagnostic tests using standard criteria are used in screening for diabetes.
When does screening take place?
Screening is undertaken in any of the following seven conditions:-
If the disease is a major public health problem – diabetes is a major health problem worldwide
The pathophysiology and course of the disease is well understood
The disease has a pre-clinical stage where there are no symptoms
There are tests that can detect the patient in these preclinical stages
If treated at these preclinical stages patients are likely to benefit
Screening tests are cost effective
Screening can be undertaken as a long term process and not merely an isolated one-time effort
For diabetes, conditions 1, 2, 3 and 4 are met.
Screening for diabetes
Screening for diabetes needs to be begun by age 45 and needs to be repeated every three years in normal persons. The decision to test for diabetes is usually based on clinical judgment and patient preference. Testing should be considered at a younger age or be carried out more frequently in high risk individuals e.g. those with a family history or obese individuals. Those presenting with symptoms of diabetes should receive diagnostic testing for diabetes.
There is a rise of diabetes prevalence especially type 2 among children and adolescents. The American Diabetes Association recommends that overweight (defined as BMI >85th percentile for age and sex, weight for height >85th percentile, or weight >120% of ideal [50th percentile] for height) youths with any two of the risk factors should be screened for diabetes. Testing should be done every 2 years starting at age 10 years or at the onset of puberty if it occurs at a younger age.
Risk factors include:
family history of diabetes
certain race/ethnic groups like Native Americans, African-Americans, Hispanic Americans, Asians/South Pacific Islanders
having insulin resistance or conditions associated with insulin resistance like high blood pressure, high blood cholesterol, polycystic ovary syndrome or acanthosis nigricans
The best screening test for diabetes is the fasting plasma glucose (FPG). This is also a vital test for diagnosis of diabetes. The FPG test and the 75-g oral glucose tolerance test (OGTT) are both suitable tests for diabetes. Fasting blood glucose test is preferred as it is faster to perform and more acceptable to patients and less expensive. A fasting blood glucose of more than 126 mg/dL or 7 mmol/L indicates further testing.
Impaired glucose tolerance is considered in individuals with FPG more than 110 mg/dL or 6.1 mmol/L but less than 126 mg/dL or 7 mmol/L. This is a risk factor for future diabetes.
The A1C test values remain a valuable tool for monitoring glycemia, but it is not currently recommended for the screening or diagnosis of diabetes.