Fresh and relaxed is how you should be and also early in the day, when taking those common but numerous “medical tests” that many of us are ordered to do by our doctors.
A battery of laboratory tests……sugar tests, lipid profile, liver function test, kidney function test, urine full report or stools for occult blood has been ordered but how many of us know the preparation required for them. To do the tests right and get the authentic results, MediScene delved into ‘Laboratory Medicine’ and spoke to two experts in the fields of “biochemical” and “haematological” reports.
It is best if you do most tests in the morning, unless otherwise specified by your doctor, stresses Consultant Chemical Pathologist Dr. Rajitha Samarasinghe, pointing out that this is because each test has a normal range specified and the standard samples have usually been taken in the morning.
It is also vital for patients to be relaxed and not be after vigorous exercise, according to this specialist, who echoes the view of Consultant Haematologist Dr. Mala Jayatilaka that if there has been strenuous walking, the person undergoing the test should relax for at least 15-20 minutes.
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| Pic by M.A. Pushpa Kumara |
This is particularly relevant for the lipid profile, as well as most of the haematological tests, MediScene understands.
When collecting samples of blood, laboratories should ensure a free-flowing sample and not one where there has been pumping, it is learnt.
Getting into important detail, Dr. Samarasinghe says when taking the common sugar (for diabetes) and lipid (for fats or cholesterol) profile, most people fast religiously, abstaining from eating food as well as drinking liquids. The fasting should be only for food and liquid, other than plain water, she says, adding that the usual amount of plain water that the person drinks should be taken during the fast.
Another issue that most people are not aware of that for the sugar test, the fasting period should be 8-10 hours while for the lipid profile it is 12 hours. So if both tests are being taken during the same fasting period, blood should be drawn for the sugar test at 8-10 hours and only after 12 hours for the lipid profile.
“If the fasting is more than 16 hours, then the tests are invalid,” emphasizes Dr. Samarasinghe. If the person undergoing the test is a diabetic and is on medication, the medication should not be stopped at the time of the test, as it would give the wrong figures which would not indicate the status of control of the disease.
For the Post-Prandial Blood Sugar (PPBS) test, meanwhile, the blood should be collected two hours after a standard meal, it is learnt.
Talking more sugar tests, Dr. Samarasinghe points out that when an Oral Glucose Tolerance Test is ordered two samples need to be taken after the fasting patient drinks the glucose liquid -- after one hour and after two hours.
It is important for the patient not to exert himself/herself by giving a sample after one hour and then leaving the laboratory to do the marketing or attend to some other business before returning to give the second sample after two hours.
The patient must remain at the lab and rest until the second sample of blood is drawn.
According to this Chemical Pathologist if the doctor who is treating a patient requires a thyroid profile, the blood test should invariably be done in the morning and the patient should under no circumstances stop taking his/her medication.
The thyroid profile is done to check whether the treatment is working and the thyroid issues are adequately controlled. If the patient stops the medication before taking the test, it would be futile.
This is because both the tests for sugar in a diabetic or thyroid profile in someone suffering from thyroid issues are “monitoring tests”, MediScene understands, while for specialized hormone tests to determine growth etc., which are dynamic function tests, the guidelines of the doctor should be followed to the letter.
Referring to the urine test for micro-albumin, which is ordered for the early detection of kidney trouble in those suffering from diabetes, she specifies that the first urine outflow early morning should be collected as the sample. “The laboratory too needs to test the sample freshly and as soon as possible. Otherwise there could be problems when checking electrolytes, sodium and even calcium.”
If a 24-hour urine test is needed, the patient needs to follow the instructions of the lab which will give a large bottle to him/her and collect urine throughout the day into that bottle, she says.
Moving from urine to faeces, both these Consultants advise that if a Stool Occult Blood test is ordered to check whether there is gastrointestinal bleeding which could be an early sign of cancer or peptic ulcer disease, the patient should stop taking oral iron, if he/she is on it, for the duration of the three-consecutive day test. The patient should also not take any worm treatment or brush the teeth vigorously as bleeding gums could stain the stools, giving a false reading.
Green-leafy vegetables and red meat which have iron should also not be eaten during this time as they too could stain the stools.
It’s all about blood
Usually for haematological (blood) tests, fasting is not necessary as sometimes fasting may produce erroneous results due to the blood being concentrated, points out Consultant Haematologist Dr. Mala Jayatilaka, underlining the fact that the results would depend on good quality samples, which are as fresh as possible.
The blood must flow freely from one prick and the blood to anti-coagulant ratio should be right, she says. If a 1ml sample is needed from a baby, which may be difficult to take, drawing 0.5ml first and then another 0.5ml and mixing them together is not the right way to do it.
When a ‘blood picture’ is required to check out cell morphology in someone, it is of paramount importance not to take blood after that person has received a blood transfusion. “Then the donor’s blood cells are mixed with the patient’s and a conclusive blood picture cannot be got. Neither can the type of anaemia be determined,” says Dr. Jayatilaka.
When doing coagulation (clotting) tests, the sample should be taken freshly, not tested after 4-6 hours later, says this Specialist Haematologist, pointing out that the ‘bleeding time’ test is a diagnostic one in the screening of certain bleeding disorders and not to ascertain whether the patient will bleed during a surgical operation. Bleeding time would depend on the platelet count and the function of the platelets. The coagulation test is not a measure of this.
When taking a Serum Ferritin test to find out the body’s iron stores, the patient should not have any infection, she says, as then the acute phase protein will be high and it will not show a realistic picture.
Some will also take a serum iron test while taking iron, which once again will not give an accurate reading, it is learnt, with this Specialist explaining that it would be similar to checking for serum B12 levels while taking the B12 injection.
With regard to the ‘blood disease’ of Thalassaemia, Dr. Jayatilaka draws the line between Thalassaemia Major and Thalassaemia Minor and when and why blood pictures are necessary.
Hb electrophoresis or a High Performance Liquid Chromatology (HPLC) test to quantify different types of haemoglobin is necessary to confirm Thalassaemia Major as it helps detect the different types of haemoglobin in the blood. Once again, this should not be done while the patient is getting blood transfusions as the donor’s blood would be mixed with the patient’s.
In the case of Thalassaemia Minor which is not a disease but indicates that the person is a carrier, it is always better to exclude co-existing iron deficiency or treat it completely before doing an HPLC since there is no treatment involved in Thalassaemia Minor. However, if an iron deficiency is not treated it has an impact on the patient’s cognitive (memory) development.
An HPLC to find the Thal trait may be necessary only before marriage, so that they may be adequately counselled about marrying a partner with Thal Minor, says Dr. Jayatilaka, adding that at the same time results of an HPLC can be affected by the presence of an iron deficiency masking the proper diagnosis.
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