Laboratory Screening of Diabetes
by Prof. Upali Gunasekara
Diabetes is considered to be one of the commonest diseases to affect mankind causing a significant number of deaths and debility. It is so common that it causes a death every five seconds some where in the world and each second a new patient is diagnosed. There are nearly 300 million patients with diabetes world wide and in Sri Lanka it could be about a million. Common symptoms of diabetes include loss of weight, thirst, passage of large amounts of urine and skin problems. The complications of diabetes include heart attacks, strokes, ulcers in the legs, amputations, kidney failure and loss of vision.. An important feature in this illness is that in nearly 50% of those affected by it have no symptoms by the time the diagnosis is made some of these patients would be exhibiting the above complications. Therefore it is crucial to identify these patients who do not exhibit symptoms of diabetes so that the dreaded complications could be prevented.. The purpose of this letter is to discuss some important aspects of screening for diabetes to commemorate the World Diabetes Day which falls on the 14th of November . This is the birthday of Sir Frederick Banting, the co-discoverer of insulin, the life saving drug used in patients with Diabetes.
There are in fact two types of screening in diabetes. It could be "Screening for Diabetes" and "Screening in Diabetes".
Screening "for" diabetes
This indicates the use of tests for the diagnosis of undiagnosed diabetes. A large number of people who don’t have symptoms of diabetes are not bothered to test for it as they consider themselves healthy or indifferent to their own health. Suitable tests are available for screening and it could be carried out in the whole population (universal screening) or screening when the opportunity arises (opportunistic screening) or screening in high risk individuals (high risk screening). Universal screening is expensive and impracticable to carry out and is therefore not practiced even in highly developed countries such as the United States. However opportunistic screening is more practicable and is the type of screening carried out when a person presents to a doctor or a hospital for any other reason The screening done at medical examinations for insurance policies and employment purposes too could be considered as types of opportunistic screening. However the type of screening that brings about a diagnosis in a large number of patients is high risk screening where a person who is at a high risk of developing diabetes is screened. Those who are at high risk of developing diabetes in the future are shown below.
1. Those with a family history of diabetes
2. High blood pressure and high cholesterol values.
3. Sedentary occupations
4. Over weight persons
5. Those who have been fat (more than 3.5kg) and those who have been very thin (less than 2.5kgs) at birth.
6. Those on diabetes producing medications.
The presence of a family history confers a very high risk for the development of diabetes. Family history includes parents, children, siblings and paternal and maternal uncles and aunts. The risk of a child developing diabetes if both parents have the condition is nearly 60% whereas if only one parent is affected it is about 40%. It is therefore advised that all those who are more than 30 years old with a family history of diabetes should be screened at least once a year.
High blood pressure (hypertension) and high cholesterol are very common among Sri Lankans. Previous studies have revealed that nearly 40% of adults over the age of 30 years have high blood pressure (There is some recent evidence to indicate that those who are just below the blood pressure levels designated as high blood pressure called "prehypertension" too are prone to develop diabetes).
Most white collar occupations in our country are sedentary. There is hardly any exercise carried out by these workers, a fair number of whom become diabetic.
Even though the problem of over weight (measured by an index called body mass index) is not common in Sri Lanka a significant number of our people have increase of weight around their waists and this is called ‘central obesity’. Central obesity is caused by the deposition of excess amounts of fat around the waist. A simple measurement of the waist could identify these people. A non elastic tape held around the waist at the most protuberant part of the abdomen indicates waist size. In a healthy male it should be less than 90cms whereas in a female it should be less than 80cms. All those who have waist measurements above this range should therefore undergo testing for diabetes.
Birth weight of individuals have a profound affect on health. New born babies whose birth weight is less than 2.5kgs or more than 3.5kg are more prone to develop conditions such as diabetes and heart disease in adult life. Since at present most people have their birth weight records all those at the above ranges should be tested for diabetes.
The over use of drugs such a predisolone which could cause diabetes is rampant in Sri Lanka. This drug is used in the treatment of conditions such as asthma and skin conditions. All those who have taken these drugs on a long term basis should be tested for diabetes.
Tests used in screening for diabetes
The commonest test used is the fasting blood sugar where a sample of blood is taken after an overnight fast of 8 to 10hours. An abnormal result does not necessarily indicate the presence of diabetes until the person is re tested three days later. The other tests used include a blood test done 2 hours after ingesting some glucose-This test is done in certain special situation. A urine test for sugar is of no value in the diagnosis of diabetes.
Screening "in" diabetes
Screening in diabetes means identification of complications of diabetes. The patient may or may not exhibit the symptoms of complications. Of these complications now a days nearly all patients are screened for high cholesterol, kidney disease and, eye disease at the time of diagnosis of diabetes. High cholesterol is diagnosed by a blood test called the ‘lipid profile’ and the likelihood of kidney -involvement by a simple urine test called ‘microalbumin’. Eye screening is carried out by an instrument called the ophthalmoscope.
In addition during the course of time some patients need screening for unsuspected heart disease, kidney disease and disease of blood vessels.
A very close association exists between diabetes and heart disease A is mandatory that all patients with diabetes are screened for heart disease under the following circumstances.
1. A typical chest pain. A patient may not exhibit the typical symptoms of a heart attack but instead would manifest with other types of chest pain.
2. Difficulty in breathing
3. High cholesterol and high blood pressure
4. Diabetes of more than 5 years duration
5. An abnormal ECG
The tests used include ECHO cardiography, stress ECG and some times even coronary angiography where a dye is injected into the blood vessels supplying the heart muscle (called coronary arteries) and an Xray taken to identify which vessels are blocked.
Screening for kidney disease is indicated in situations where there is protein in the urine and uncontrolled blood pressure. The tests include urine tests, blood tests as well as X rays and scans-Tests used to determine the condition of the blood vessels supplying the legs include Doppler and arteriography where as in the case of the heart a dye is injected into the blood vessels of the legs to determine their patency.