The diagnosis of type 1 diabetes and many cases of type 2 diabetes is usually prompted by recent-onset symptoms of excessive urination and excessive thirst often accompanied by weight loss. A diagnosis of diabetes is made when any three of these tests is positive, followed by a second positive test on a different day:

1. Fasting plasma glucose of greater than or equal to 126 mg/dL with symptoms of diabetes
    
2. Casual plasma glucose (taken at any time of the day) of greater than or equal to 200 mg/dL with the symptoms of diabetes
    
3. Oral glucose tolerance test (OGTT) value of greater than or equal to 200 mg/dL measured at a two-hour interval. The OGTT is given over a three-hour time span.

Diagnosis of Gestational Diabetes:
Gestational diabetes is diagnosed with a 50 gram glucose screening test, which involves drinking a glucose drink followed by measurement of the blood sugar level after one hour.

Diabetes mellitus is characterized by recurrent or persistent hyperglycemia, and is diagnosed by demonstrating any one of the following:

Diagnosing Diabetes
Stage	Test (mmol/L -- mg/dl)
	Fasting Plasma Glucose Test (FPG) (Preferred) 1	Casual Plasma Glucose Test	Oral Glucose Tolerance Test (OGTT) 75 gram load
1. Normal	Fasting Plasma Glucose (FPG) less than 5.6 / 100	N/A	Two-hour plasma glucose (2hPG) less than 7.8 / 140
2. Impaired Glucose Tolerance	Impaired Fasting Glucose (IFG) = FPG greater than or equal to 5.6 / 100 and less than 7.0 / 126	N/A	Impaired Glucose Tolerance (IGT) = 2hPG greater than or equal to 7.8 / 140 and less than 11.1 / 200
3. Gestational Diabetes	Fasting Plasma Glucose (FPG) greater than or equal to 7.0 / 126 2	N/A	Two-hour plasma glucose (2hPG) greater than or equal to 8.6 / 155 <>
4. Diabetes	Fasting Plasma Glucose (FPG) greater than or equal to 7.0 / 126 2	Casual Plasma Glucose greater than or equal to 11.1 / 200 plus symptoms 3	Two-hour plasma glucose (2hPG) greater than or equal to 11.1 / 200 4

Notes:

1. The FPG is the preferred test for diagnosis, although any of the three is acceptable. In the absence of unequivocal hyperglycemia with acute metabolic de-compensation, one of these three tests should be used on a different day to confirm the diagnosis.
2. Fasting is defined as no caloric intake for at least eight hours.
3. Casual is defined as any time of day without regard to time since last meal; symptoms are the classic ones of polyuria, polydipsia, and unexplained weight loss.
4. OGTT should be performed using a 75 gram glucose load. The OGTT is not recommended for routine clinical use.

Prevention and Treatments

Generally, the risk of developing diabetes increases with age. The disease can also affect women during pregnancy, leading to complications for both mother and child. The treatment of diabetes requires daily insulin injections, proper nutrition and regular exercise.
 
Type I
Currently there is no way to prevent type 1 diabetes. Type I diabetes have seen improved control with intensive insulin therapy, using multiple daily injections or an insulin pump.

Type II
New pills for the treatment of Type II diabetes are now available. Many cases of Type 2 diabetes could be prevented or delayed through simple lifestyle changes, maintaining an ideal body weight that lower the risks of diabetes and other chronic diseases, such as cardiovascular diseases and cancer.

Gestational Diabetes
A cure for Diabetes has not been found yet.  Treatment involves taking steps to keep your blood glucose levels in a target range. However, your blood glucose levels can be controlled by:

1. Maintaining blood glucose levels,
2. Maintaining blood fat levels and
3. Maintaining weight
4. Changing your meal plan
5. Physical activity
6. Insulin (if needed)