Each laboratory has specific methods, calibrations and controls of blood analyses. However, how should you prepare for blood analyses?
Which factors should you avoid in order to get the most accurate results?
Most often, blood analyses are affected by food intake. This means that it is best to take the blood sample in the morning (on an empty stomach), 12 hours after the last meal. For example, if your blood analyses is appointed for 8am, then your last meal should be at 8pm the previous day. This is necessary because food consumption in the period prior to blood analyses leads to an increase in the concentration of glucose, triglycerides, proteins, iron, electrolytes, as well as a number of other bio chemical metabolites.
It is recommended that a day before blood analyses you consume light food which is not rich in fat and sugar (avoid mayonnaise, mustard, whole dairy products, like cheese, lamb, pork, chocolate, oriental sweets, cakes) and have a light meal by 8pm at the latest.
Before coming to the lab for blood analyses you should have some water, because it often happens that the patient comes dehydrated from the night’s sleep and we can not perform the process of venipuncture (taking blood). I must say that a glass or two of water does not affect the laboratory test.
The Oral Gluose Tolerance Test (OGTT), golden standard in discovering diabetes, takes two hours, 120 minutes, and is performed in the laboratory. The test for men and women who are not pregnant is performed in two phases: first on an empty stomach and then, two hours after the patient has had the solution given by the nurse. During the test procedure the patient must rest and is not allowed to eat, drink or smoke. Several days before the test the patient should restrain from hard work. The patient should stop taking medicaments that may affect the glucose metabolism (ex. corticosteroids), but only after having consulted the doctor. It is important to have abundant sugar intake three days before the test. The test is performed in the presence of medical professional.
In case the patient takes therapy, there are specific rules how to handle the therapy before the blood test. The patient must inform the lab about the kind of therapy s/he takes. Patients who take oral anticoagulant therapy should have the test done in the morning, and have their regular therapy after the blood test.
Talking of the impact of the therapy over the laboratory analyses, no matter what kind of therapy is in question, like: iron supplementation for anemia reasons, or antibiotics for infection, or hormonal therapy, you should consult your doctor to arrange a wash out period (time necessary to clean the body of the medicaments) which lasts 7-10 days and then have blood sample taken. If you are to test CK (Creatine Kinase) or LDH (Lactate Dehydrogenase), you should avoid physical activities since they increase the levels of these muscle enzymes.
Taking blood for prolactin, cortisol, ACTH, catecholamines, takes 20-30 minutes and the patient must be completely relaxed and laid. This type of hormones vary in levels throughout the day, therefore it is recommendable to do the analyses from blood sample taken early in the morning.
The analyses of three-month glycated hemoglobin or HBA1c test, is not related to food intake. The test determines the average sugar level in the blood within three months, so it is irrelevant whether the blood is taken in the morning or in the afternoon, or on an empty stomach or not. The same goes for the thyroid hormones (TSH and FT4), blood sample can be taken any time of the day, irrelevant of the food intake. Further no-risk parameters, that do not depend on food and need no special preparation procedure, are: thyroid gland antibodies (anti TPO and anti Tg), then, infection marker (CRP), all infective viral markers (hepatitis A markers (HAV IgG and HAV IgM, hepatitis B markers (HBsAg I), hepatitis C markers (Anti HCV) and anti AIDS, as well as tumor markers etc.
Marija Dimkovska Ribarova, MS, graduated engineer in biochemistry