Diabetes is always a slow progressive disease marked by its mild and occult symptoms. Because of its complications in short and long term, it is crucial to diagnose it as early as possible. This is the importance of the disease screening.
Nonpregnant adults:
Multiple professional organizations have published screening recommendations for type 2 diabetes, although slight differences exist (. Based on cohort studies, the American Diabetes Association (ADA) recommends screening a broader population based on risk, including all adults 45 years or older regardless of risk, and includes screening for prediabetes in the guidelines.
Screen asymptomatic adults with a body mass index ≥ 25 kg per m2, and one or more additional risk factors:

• A1C > 5.7%, impaired glucose tolerance, or impaired fasting glucose on previous testing
• Acanthosis nigricans
• Cardiovascular disease
• First-degree relative with type 2 diabetes
• HDL cholesterol level < 35 mg per dL and/or a triglyceride level > 250 mg per dL
• High-risk ethnicity: black, Native American/Alaska Native, Hispanic/Latino, Asian American, and Native Hawaiian/Pacific Islander
• Hypertension (blood pressure > 140/90 mm Hg or taking medication for hypertension)
• Physical inactivity
• Polycystic ovary syndrome
• Women who had gestational diabetes or who delivered a baby weighing > 9 lb

In persons without risk factors, testing should begin at 45 years of age
If test results are normal, repeat testing should be performed at least every three year
Pregnant women:
Hyperglycemia increases the risk of congenital malformations and intrauterine fetal death. Women with gestational diabetes mellitus (GDM) who have fasting hyperglycemia have a three- to fourfold increased risk of infant malformations. The goal of screening is to reduce maternal and fetal complications such as preeclampsia, cesarean delivery, congenital malformations, macrosomia (and later childhood/adolescent overweight), shoulder dystocia, nerve palsy, bone fracture, jaundice, and infant death
The ADA advises screening pregnant women in their first trimester if they have risk factors for developing type 2 diabetes or GDM:

• obesity,
• advanced maternal age (older than 35 years),
• history of GDM,
• family history of diabetes, and
• belonging to a high-risk ethnic group.

Screening for GDM should be performed using a two-step 50-g nonfasting oral glucose challenge test; if the result is positive, this is followed by a diagnostic 100-g fasting oral glucose tolerance test
Children:
The ADA recommends screening children and adolescents 18 years and younger who are:overweight (i.e., body mass index greater than 85th percentile for age and sex, weight for height greater than 85th percentile, or weight greater than 120% of ideal [50th percentile] for height) and who have any two of the following risk factors:

• history of type 2 diabetes in a first- or second-degree relative, \
• belonging to a high-risk ethnic group (Table 18,16–20),
• acanthosis nigricans,
• hypertension,
• hyperlipidemia,
• polycystic ovary syndrome.35

The American Academy of Pediatrics and the ADA recommend screening at-risk patients every two years starting at 10 years of age, or at onset of puberty if before 10 years of age.
Older adults:
 No organizations currently recommend routine screening in geriatric patients, although the ADA does support the consideration of screening to prevent complications that could lead to functional impairment. Although treatment goals may differ in older patients, diagnostic thresholds