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The classic symptoms of diabetes are excessive thirst, excessive hunger, excessive urination, weight loss, and genital pruritus. This is the clinical picture that usually is seen in juvenile diabetes. In adults, and especially older adults, the disease frequently is relatively symptomless or even completely asymptomatic.

The diagnosis of diabetes usually is dependent upon laboratory pro­cedures, the most important of which is the finding of increased concen­trations of glucose in the blood. In many cases the diagnosis can be established with a single one-hour postprandial quantitative blood glucose determination, which, using any of the true glucose methods, should not be above 160 mg percent. Fasting blood sugar determinations are less helpful than postprandial tests, being so much less sensitive that one third of the cases will be missed if these determinations are used.

When a single blood sugar determination does not permit a diagnosis of diabetes or yet rule out the disease, it is necessary to do a glucose tolerance test. To give the maximum amount of information about carbo­hydrate metabolism, the glucose tolerance test should be preceded by a regimen of three days on a high-carbohydrate diet (250 gm of carbo­hydrate per day). The test involves three blood sugar determinations: after fasting and one and two hours after the ingestion of 100 gm of glucose solution.

The interpretation of the glucose tolerance test is not uniform with all physicians. One practical system is as follows:

Maximum Glucose Level*
Fasting 110 mg % — 1 point if higher
1 hour 170 mg % = 1 point if higher
2 hours 120 mg % = 1 point if higher
3 hours 110 mg % = 1 point if higher * True glucose method {Soraogyi-Nelson).

In a person with two or more points, the presence of diabetes mellitus may be considered as established. With only one point, the person tested should be considered as a "potential diabetic" or a "prediabetic" and should be followed accordingly.