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Diagnosis of Diabetes

Diabetes is first detected under various circumstances.

The symptoms of acute diabetes are so dramatic that it is almost impossible to miss the diagnosis. But in a number of patients, diabetes develops so gradually and silently that it is revealed only by the methodical examination of the urine and the blood. It is believed that undiagnosed diabetics probably outnumber known diabetics.

It is precisely for this reason that all persons above 35 years of age, especially if they are obese or have a family history of diabetes, should get their urine and blood examined at regular intervals of time, to ascertain the presence or absence of diabetes. Actually most of these tests are utterly simple and can be learnt or performed by every interested person.

Diagnostic investigations:

(A) Tests to detect the presence of sugar in the urine (glycosuria) :

(1) Benedict's Test : This is a very simple and effective method of ascertaining the presence or the amount of glucose in the urine and can be done by the diabetic himself.

Apparatus :

Benedict's solution (fresh; certainly not more than 3 months old),



Test-tube holder.

Procedure :

Take 5 ml (one teaspoon) of Benedict's solution in the test-tube.

Holding the test-tube with the holder, heat it over a spirit lamp till the Benedict's Solution boils without overflowing.

Drop 8 to 10 drops of urine into the boiling Benedict's solution.

After again boiling the mixture, let it cool down.

While cooling, the mixture changes colour.

The colour of the mixture serves as a guide to the amount of sugar in the urine: blue-sugar absent; green-0.5 % sugar; yellow-1 % sugar; orange-1.5 % sugar; brick red-2 % or more sugar.

The concentration of sugar in the urine can also be judged by matching the colour of the urine with one of the colours given below :

Note : It is essential that the above test be performed two hours after a meal. In the initial stages of the disease, a diabetic does not lose sugar in his urine, when on empty stomach. Hence if the Benedict's test is performed in the fasting state, it is possible to miss the diagnosis of the disease.

Even if sugar is detected in the urine by Benedict's test, the diagnosis of diabetes should be confirmed by blood­analysis. Sometimes sugar may overflow into the urine even without its concentration being high in the blood. This is a benign condition, termed 'renal glycosuria'.

Thus Benedict's test does not have a diagnostic significance. It is more important to ascertain the degree of control of the disease, in a person who is undergoing treatment.

Efforts have been made to devise tests simpler than this test. One such test is 'clinitest'. Clinitest tablets are available in the market. First, a mixture of 5 drops of urine and 10 drops of water is taken in a test-tube. A clinitest tablet, when dropped into the test-tube, makes the mixture boil on its own. The hot mixture gradually changes colour. A colour-chart provided with the tablets can be used to match the colour of the urine and hence judge the amount of sugar present.

The note given below the Benedict's test is applicable to clinitest too.

(2) Glucose oxidase test : Paper or plastic strips, called diastix or tes-tape are available in the market. A colour-chart is provided along with the strips. While passing urine two hours after a meal, the person has to hold a tes-tape or a diastix strip in the urine-stream for a few moments. The strip changes colour on coming in contact with the urine. After 30 to 60 seconds the colour of the strip should be matched with one of the colours of the provided chart to assess the amount of sugar in the urine.

Both the above tests are more simple and sensitive than Benedict's test; but they are somewhat expensive. They are very useful to a person who is away from home.

The note given below Benedict's test is applicable to glucose oxidase test as well.

(B) Tests to detect the amount of sugar in the blood : It should be noted that a certain amount of sugar is always present in the blood and necessarily so. In diabetes, the blood-sugar level rises above the normal or physiological limits.

(1) Fasting blood-sugar : A sample of the blood is obtained when the person is in a fasting state and the amount of sugar is assessed.

This test alone is not adequate for the diagnosis of diabetes because in early or mild diabetes, the blood-sugar values may be normal in the fasting state. Thus a diagnosis of diabetes may be missed.

However, if the amount of blood-sugar in the fasting state is found to be greater than 140 mg % on two separate occasions, it is a sure indication of diabetes.

(2) Post-prandial blood-sugar (amount of sugar in the blood after a meal or after consuming 75 gms of glucose) : A blood sample is obtained two hours after having a carbohydrate-rich meal and the amount of sugar present is determined.

According to the WHO criterion, if the amount of blood-sugar two hours after a meal is greater than 200 mg % on two separate occasions, diabetes is present. Blood-sugar values between 140 and 200 mg % should be termed 'impaired glucose tolerance'.

This is a more reliable test to diagnose diabetes than fasting blood-sugar estimation.

(3) Glucose tolerance test : This is a superb test to evaluate the metabolism of dietary carbohydrates in the body.

Certain precautions should be taken before undergoing this test.

During the three days preceding the test, the person should eat a carbohydrate-rich diet. During this period, cortisone group of drugs and other drugs like nicotinic acid, Vitamin C, aspirin, thiazide diuretics and oral contraceptives should not be taken.

After taking the evening meal on the day prior to the test-day, the person should not eat or drink anything. He should not even smoke. On the test-day, the person should go for the test early in the morning, with an empty stomach.

First of all, urine and blood samples are collected to determine fasting urine-sugar and blood-sugar. The person is then given to drink a solution containing 75 to 100 gms of glucose and a few drops of lemon juice. Thereafter, blood and urine samples are obtained every half an hour, for the next 2½ hours and analysed for the amount of sugar. On the basis of these findings, the efficiency of the body to metabolise dietary glucose is known.

The following characteristics are seen in a healthy person during this test:

  1. Fasting blood-sugar level is less than 120 mg % (many a time 100 mg %).
  2. The amount of glucose in the blood rises to a maximum value in 30 to 60 minutes after the meal. This maximum value is not more than 160 mg %.
  3. Two hours after the meal, the blood-glucose level comes down to the fasting level.

Diabetics, on the other hand, show the following characteristics during this test:

  1. Fasting blood-sugar level is equal to or greater than 140 mg%. However, in early or mild diabetes the value obtained may be a little lower, say 120 mg %.
  2. After the meal; the concentration of blood-sugar takes more than an hour to reach the maximum value. This maximum value is equal to or greater than 200 mg % (WHO criterion). However in early or mild diabetes the maximum value obtained may be 180 mg %.
  3. Two hours after the meal, the amount of blood­glucose is still quite high (140 mg % or more) as compared to normal.

The graph, plotted on the basis of blood-sugar values obtained during glucose tolerance test, is called 'glucose tolerance curve'.

(4) Stress (steroid primed) glucose tolerance test:

This test is more important to detect prediabetes or latent diabetes. The logic behind this test is that if persons with a possibility of developing diabetes in future (especially those having a family history of the disease) are given, besides glucose, a steroid drug like cortisone (50 mg) or prednisone (10 mg) or triamcilone (8 mg), a physical state resembling diabetes develops; such a diabetes-like state cannot be developed in healthy persons even with steroid drugs.

The procedure of this test is exactly similar to that of glucose tolerance test. After the person consumes 75 gms of glucose and the steroid drug (in above-mentioned amount), blood samples are periodically drawn from his body. If the blood-sugar is 160 mg or more after one hour or 140 mg or more after two hours, the person may be considered to be in prediabetic or latent-diabetes state and may develop frank diabetes in the future.

(5) Glycosylated haemoglobin test : This test is not important to detect diabetes. It is more important to judge the control of diabetes during a period of 6-10 weeks prior to the test, in a person undergoing treatment for the disease.

The haemoglobin present in the red blood corpuscles has a tendency to get bound to glucose. The greater the blood-glucose concentration, the greater is the amount of glucose-bound (called glycosylated) haemoglobin. Such glucose-haemoglobin linkage is quite stable and lasts for 60 to 120 days (the life-span of red blood corpuscles). Thus the amount of glycosylated haemoglobin is a sure guide to the concentration of glucose in the blood during the past 6-1 0 weeks (i.e., the degree of control over the disease achieved).

To detect the amount of glycosylated haemoglobin, the blood is passed through a chromatographic column, where glucose-bound haemoglobin separates out from normal haemoglobin.

This test is most important for pregnant diabetic women because uncontrolled diabetes may risk the lives of the mother and the child; therefore ignorance about the degree of control of the disease is undesirable.

Other investigations which may help the diabetic : Laboratory investigations are inevitable to assess the degree of control achieved while treating diabetes. Of such investigations urine-sugar estimation is the most common and important investigation.

Besides, there are other investigations which help to detect complications of diabetes. These include the estimation of acetone, albumin and chlorides in urine.

The presence of acetone in the urine is an indication of ketosis. On detection of acetone, rapid steps should be taken to prevent diabetic coma.

The presence of albumin in the urine is an indication that something is wrong with either kidneys or the ureter.

The estimation of the amounts of chlorides in urine gives information about the state of electrolyte-balance in the diabetic's body.

Rothera's Test for acetone:

  1. Take a test-tube. Fill up a third of it by solid ammonium sulphate.
  2. Add 5 ml of urine to the test-tube.
  3. Add 8 -10 drops of 0.25 % sodium nitroprusside solution.
  4. Finally add to the test-tube, 1-2 ml of concentrated ammonia solution.

Presence of acetone or aceto-acetic acid in the urine is indicated by permanganate-like purple colouration of contents of the test-tube.

Gerhardt's test for aceto-acetic acid :

  1. Take 5 ml urine in a test-tube.
  2. Add to it, drop by drop, a 3 % ferric chloride solution. A white precipitate of ferric phosphate will be formed.
  3. Add some more ferric chloride and filter the contents of the test-tube through a filter paper.

A purple or dark brown colouration of the filterate indicates the presence of aceto-acetic acid in the urine.

Sulphosalicylic test for albumin:

  1. Filter the urine.
  2. Take 1 ml urine in a test-tube.
  3. Add to it 1 ml of sulphosalicylicacid (concentration: 30 gms in 100 ml).
  4. Let the mixture stand for 10 minutes.

A milky or cloudy appearance of the mixture indicates the presence of albumin; a clear solution is an indication of its absence.

Another test for albumin :

  1. Fill up 2/3 of the test-tube with urine.
  2. Drop a red litmus paper into the test-tube. If the urine is alkaline it will turn the litmus paper blue. Now add to the test-tube, 10% acetic acid drop by drop. After every drop, shake the test-tube vigorously. Stop adding acetic acid as soon as the litmus paper is seen to turn red.
  3. Now hold the test-tube slightly inclined and heat the upper part of the mixture on a spirit lamp.
  4. A cloudy or milky appearance of the mixture indicates the presence of either albumin or phosphates.
  5. To the milky mixture, add 10% acetic acid drop by drop. Simultaneously, heat the test-tube. Disappearance of the milkiness is an indication of phosphates and persistence of milkiness is an indication of albumin in the urine.

Test for chlorides :

  1. Take 25 ml of urine in the test-tube.
  2. Slowly add to it, 10 drops of concentrated nitric acid.
  3. Finally add 2-3 ml of 3 % silver nitrate solution.

Normally a curd-like white precipitate forms in the test-tube. If the electrolyte-balance inside the body is disrupted, the amount of chlorides in urine decreases. Then the white precipitate does not form (or forms very slightly).

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