There are several tests to diagnose diabetes mellitus. Some of the tests can be carried out at the household level, while there are some sophisticated ones that are carried out only in clinics. Whatever be the case, the diagnostic tests of diabetes mellitus are quite efficient in finding out the onset of the disease.

The tests of diagnosis of diabetes mellitus are classified into three main categories:-

  • Urine Tests
  • Blood Tests
  • Glucose Tolerance Tests

(1) Urine Tests

(i) Benedict’s Test

The Benedict’s reagent is used to determine the presence of sugar in the blood at the household level. A sample of the urine is collected and a few drops of the Benedict’s reagent are put into it. The quantity is 5 drops of Benedict’s reagent in 8 drops of urine sample. The solution is warmed until coloration is formed. The nature of the color gives the idea of sugar content in the urine.

The following chart is used to estimate the percentage of sugar in the blood.

Color Obtained

Percentage of Sugar in the Blood



Clear Green


Turbid Green


Green and Yellow (Precipitate formation)

0.5 to 1.0





Brick Red

More than 2.0

Hence, the Benedict’s reagent test is a very simple test for the confirmation of sugars in the urine. But the test is no longer used at a clinical scale for the following reasons:-

  • The Benedict’s test is not a definitive test for glucose. It is an aldehyde test. Hence, it will give coloration even if other sugars are present in the urine, such as maltose, galactose, fructose, sucrose, etc.
  • Some antibiotics can give positive results due to presence of aldehyde groups in them. Examples are aspirin, penicillin and vitamin C antibiotics.
  • The Benedict’s test shows results only when the blood sugar is increased by more than 180mg%. Hence, mild cases of diabetes mellitus cannot be confirmed.

(ii) Dipstick Tests

Dipstick tests are also color tests to ascertain the presence of sugars in the urine. Dipsticks are actually strips of paper that change their color in presence of sugars. The change of color depends on the chemicals used in preparing the dipstick. Each dipstick comes with its own manual for decoding the color information.

Again, dipstick methods are not very confirmative, because of the following reasons:-

  • Being color tests, there is a liability that the results could be misinterpreted.
  • Dipsticks are generally costly, so people do not tend to use them on a daily basis.
  • Other ketonic and aldehydic groups can interfere with the results.

(2) Blood Tests

(i) Blood Sugar Test

The person is made to fast for a day (minimum10 to 14 hours) and then some quantity of their blood is taken for the test. The blood is extricated from a vein or capillary. Once this sample is procured, the estimation of the amount of sugar in the blood is done through methods such as:-

  • ELISA – Enzyme-Linked Immunoabsorbent Assay
  • RIA – Radio-Immuno Assay

The sample can also be tested using dipsticks.

The problems that occur with the blood sugar test are:-

  • The test shows results for glucose presence only if the concentration is high. So, mild cases of diabetes mellitus can be overlooked.
  • The test may give wrong results if the fasting has not been done properly. Even a cup of tea or coffee or a single fruit can cause erroneous results.

(ii) Random Blood Sugar Test

The random blood sugar test is called so because it is taken at any time of the day and without imposing any dietary restriction on the patient, like the fasting condition mentioned above. Naturally, this test is not a very decisive test. It confirms the presence of glucose only if the recorded sugar values are more than 250 mg%.

(3) Glucose Tolerance Test

(i) Post Prandial Sugar Test

The human body normally takes two to two and a half hours to digest sugars completely. After this period, the body returns back to its normal fasting state. In case the sugars are still persistent in the blood after this length of time, then it is indicative of a faulty metabolic process, which marks the onset of diabetes mellitus.

The patient is given glucose water in a much diluted quantity and a blood test is conducted after two to two and a half hours.

This test is much better test than the others in order to understand the correct body capacity in utilizing glucose. However, the test is subjective. If the person has done any physical activity after the glucose intake, then lower values will be recorded; or if the person has had a nap, then the values recorded will be higher. Similarly, if the person has vomited or had an antibiotic like aspirin, then the recorded values will certainly be lower.