Contents
Preparation for research is an extremely important stage that has a great impact on the quality of the results obtained. Improper preparation can falsify the results and lead to a misdiagnosis. What should you pay special attention to?
Time of download
It is recommended that blood be collected for testing in the morning, between 7 am and 9 am. Why then? You could say that it is easiest to fast then, but this is only part of the truth. The release of many substances in the body depends on the time of day, emotions, exercise, and even the season. Hormones that we test frequently (including TSH and FT4) are released in the circadian rhythm: their concentration in blood serum changes with the time of day. The reference values (with which the result should be compared) refer to the morning hours. The highest concentration of TSH is reached late in the evening and at night, the lowest around noon. The difference in concentrations is approx. 2 mIU / l, which, with reference values of 0,27-4,2 mIU / l, may contribute to a misdiagnosis. The value at which we should start treatment of hypothyroidism is 4 mIU / l. So if in the morning we would get a TSH result of about 5 mIU / l, and TSH is determined in the blood collected at about 12 o’clock, we will obtain a result within the range of normal values (e.g. 3), which may result in not taking the necessary therapy. Daily fluctuations also show such parameters as: iron, phosphorus, potassium, zinc, copper and erythropoietin.
Diet
We should come on an empty stomach for a blood donation. This ensures a sufficiently long fasting time necessary to obtain correct results. If it is not enough, protein, bilirubin, AST, ALT, ALP and LDH, lipid parameters, glucose, creatinine, urea, sodium, and even the number of leukocytes can change. After a meal, white blood cells have to “test” what we have eaten – an excess of leukocytes and an increased percentage of monocytes are normal reactions in this situation.
What does it mean to be fasting? We come after a break of at least twelve hours from the last meal, which should be easily digestible and dairy-free. This is especially important when examining the lipid profile, i.e. the fractions of cholesterol and triglycerides. If we eat a meal rich in fat for dinner, incl. in cheeses, the results will reveal undigested fats from your dinner, not the cholesterol we want to test. This can result in up to a fivefold increase in individual cholesterol fractions. We will then get completely wrong results. Apart from an easily digestible dinner, on the day before the test, it is recommended to follow a diet typical of your lifestyle – both overeating and starving yourself may distort the result.
On the day of the examination, we should also refrain from drinking coffee, even black, without additives. It affects the hormonal balance, the concentration of glucose and bile acids. It can also fake bilirubin levels and lower cholesterol. In addition, coffee leaches magnesium and therefore affects its serum concentration. Instead of coffee, take 2-3 sips of clean water in the morning. This will make it easier to cope with hunger. Most sources say that you can drink up to half a glass of water if you need to. However, if it is not necessary, then the less the better.
All medications should be taken after blood sampling (unless it is not harmful to your health and unless your doctor decides otherwise). Vitamins, herbs and supplements should be discontinued 3-5 days before the test. Otherwise, the concentration of the tested parameter may be overestimated. Some vitamins interfere with the assay method. Therefore, it is recommended, for example, to avoid taking vitamin C at least 48 hours before the planned tests (this especially applies to urinalysis). Herbal preparations, in turn, may affect the concentration of certain elements, the work of enzymes and the hormonal balance.
Another substance that should not be consumed for several days before the test is alcohol. It contains sugars, and sometimes it is additionally sweetened, so if we drink even one beer before going to bed, it may affect the blood test results and also the urine analysis. If we want to determine GGTP activity, it should be avoided for three weeks before the test.
All the tips given above are recommendations only. It happens that the doctor / dietitian wants to check how the body functions under the influence of a specific substance. So if the person referring us to the test recommends a different preparation, follow his instructions.
Collection point
Laboratory diagnostics has developed rapidly in recent years and is additionally commercializing. Collection points are located in hospitals, clinics, shopping centers and service points. If we are referred for tests by a doctor under an agreement with the National Health Fund, we usually cannot choose the collection point. However, if we do research privately, it is worth using the points that are directly adjacent to the laboratory. This can have a significant impact on several parameters, including on ESR (Biernacki’s reaction), morphology, coagulation system or glucose concentration. ESR should be assessed within two hours of blood collection. Even if the determination is not performed on the same day as the collection of the material, our sample will be protected in the laboratory against factors such as temperature or light. It is worth noting that most laboratory parameters are stable, unchanged for many hours after collection.
Physical effort
In the week leading up to testing, we should maintain a normal level of physical activity. It means something completely different to each of us – if you’ve been training five times a week for a year, there’s no reason to give up exercise. You shouldn’t just increase their intensity. Effort immediately before collecting blood may cause the blood to thicken by up to 10%, moreover, the body will use more energy substances, and therefore the levels of glucose and triglycerides will decrease. Under the influence of exercise, especially in beginners, there is microdamage to the muscles, which is most often manifested by the so-called acid acids, and the concentration of enzymes present in muscle cells (LDH, AST, CPK) increases in the blood serum. The body may also respond to sudden physical activity with a systemic inflammatory reaction, resulting in an increase in white blood cell counts and ESR. Exercise can also lead to slight proteinuria and hematuria.
Stres
The results may be influenced by both long-term stress, related to e.g. work situation, and short-term stress, caused e.g. by an argument in the queue for the examination. Under the influence of stress, they increase e.g. aldosterone, angiotensin, catecholamines, cortisol, prolactin, renin, somatropin, TSH, vasopressin, albumin, fibrinogen, glucose, insulin, lactate, and cholesterol.
Body position. The concentration of some substances may fluctuate due to changes in body position. While in hospital, we often lie down and sit down abruptly for examination. This may increase the concentration of parameters such as protein, calcium, hematocrit, cholesterol, and the number of white and red blood cells. They can differ by up to 15% from those measured at rest.
Monthly cycle
In women, the day of the menstrual cycle can also affect the results. Sex hormones (including LH and FSH) are particularly susceptible to this. Depending on what you want to check, you should examine them at the right moment. It is best to consult a doctor beforehand. If we test sex hormones before visiting a doctor, it is worth remembering on which day of the cycle the blood was taken.
Preparation for research in a nutshell
- It’s best to go for a blood test in the morning.
- A good idea for a pre-test dinner is cream soup or salad. The meal should be neither sweet nor fatty.
- It is worth doing blood tests in the same laboratory.
- Before testing, you should not be physically active unless you have been training regularly for a long time.
- Before the tests, it is worth discontinuing supplements and herbs for 3-5 days.
- It is a good idea to avoid stress before testing.
- Women should avoid testing during menstruation.
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