False positive test result: what affects the indicators. Factors influencing test results Affect test results by
What are the dos and don'ts before a blood test?
Did you know that in order to get reliable test results, you need to prepare for donating blood? Online laboratory Lab4U has written a comprehensive guide for you on how to donate blood.
Don’t forget: Taking blood tests requires compliance with the rules: the procedure must be carried out by qualified medical workers who know all safety standards, and at the same time you must be in emotional and physical peace. Also, nowadays it is not customary to take blood from a vein with a syringe; for this there is a special system with vacuum tubes - a vacutainer. However, that's not all. The final conclusion can be influenced by your diet, habits and even workouts.
Are you planning to donate blood soon? Check if there is a Lab4U online laboratory near you and pay up to 2 times less! Permanent discounts up to 50% on most necessary tests!
ContentDo's and Don'ts before
Drink: Drink water in the usual amount, and for children you can even increase the portion a couple of hours before donating blood. This will reduce the viscosity of the blood and make the collection easier. Avoid sugary drinks and alcohol, alcohol affects the number of white blood cells and is eliminated from the body in only three days.
Eat: Eat your last meal 8 hours before your test. It is best to have dinner and come to the laboratory in the morning on an empty stomach. You should especially avoid eating fatty foods, as they can lead to chylosis, which will make the sample completely unsuitable for research.
Loads: It is advisable to avoid really hard workouts and a lot of stress the day before the blood test. A bathhouse is contraindicated, as is swimming in an ice hole; all this will affect the final results.
Do's and don'ts before biochemical tests:
Drink: Drink as usual, but make sure it is water and not soda or alcohol. It is advisable to eliminate coffee and tea one day before.
Eat: Before a biochemical blood test, there are most restrictions on food. The day before donating blood, it is necessary to exclude from the menu fatty foods (it will affect the indicators), sweets in large quantities, even grapes (the biochemical complex includes measurement), purine-rich foods such as meat, liver, legumes (so as not to mislead the doctor with high uric acid level). It is necessary to take the test on an empty stomach; you can have your last meal 8 hours before the procedure.
Medicines: All unnecessary medications must be eliminated the week before blood donation. But if you have medications prescribed by your doctor that cannot be canceled, do not be discouraged, indicate the names and dosages on the referral itself.
Even if you were inattentive and had a heavy breakfast on the day of the test, don’t be upset. Instead of having to go and donate blood and pay for results that may be incorrect - Just 3 clicks and any of our medical centers will be waiting for you at convenient time. And 50% discount on everything biochemical research will relieve you of stress!
Do's and don'ts before hormone tests:
Drink: There are no water restrictions.
Eat: Like all other tests, it is advisable to take hormones in the morning on an empty stomach. Eating a large breakfast may affect the readings or make the sample unusable for analysis.
Loads: Human hormones react to physical activity and stress very noticeably. From training the day before, your production may change, stress affects cortisol levels and. Therefore, if you are donating blood for tests, we advise you to avoid nerves and fuss as much as possible on the morning of the test and the day before. In the case of tests for sex hormones, exclude training, baths, and try to sleep for a sufficient amount of time.
Medicines: To test for it, it is better to exclude iodine preparations 2-3 days before donating blood; we recommend checking your multivitamins, they may contain iodine.
Other: do not forget that women need to take tests for sex hormones on certain days of the cycle; it is usually recommended to take tests on days 3-5 or 19-21 menstrual cycle, depending on the purpose of the study, unless the attending doctor prescribes other dates.
Do's and don'ts before testing for infections: PCR and antibodies
Tests for infections can be either the determination of antibodies in the blood serum, in which case all general preparation rules apply to blood donation, or the determination of infections PCR method, the material for which is taken using the urogenital smear method.
Drink: There is no need to increase the amount of water you drink, drink as much as you feel thirsty. You should especially not drink alcohol before testing for infections; it can serve as a provocation.
Eat: food has a lesser influence on the results of tests to detect infections. However, try to eat no later than 4-5 hours before donating blood and still avoid fatty foods.
Loads: If you are donating blood, cancel your workout, bath, or sauna the day before the procedure. In the case of a urogenital smear, this is not so important.
Medicines: You definitely risk getting an unreliable test result for infections if you start taking antibiotics before the test! Be careful, if treatment has already begun, identifying infections will be difficult! With the rest of the medications, everything is as usual - it is better to cancel it, if it is impossible to cancel it, indicate the names and doses on the directions.
Other: A urogenital smear must be taken by a doctor, so do not forget to make an appointment for the procedure in advance at a certain time. Men are advised not to urinate for 1.5-2 hours before taking material from the urethra. It is unacceptable to take material from women during menstruation and within 3 days after their end.
Tests for hormones and infections can be expensive, especially if you take more than one test, more than once. Lab4U offers you comprehensive examinations with a 50% discount.
What and how can affect the test results?
Why do we insist so much on eliminating food and especially fatty foods before donating blood? If this rule is not followed, your sample may not be suitable for analysis due to chylosis. This is a condition when the content of triglycerides (fat particles) in the blood serum is exceeded, it becomes cloudy and cannot be examined.
Alcohol affects so many blood parameters that it would be difficult to list them. This includes blood glucose, the content of red blood cells, the content of lactate in the blood, and uric acid. It’s best to just remember that 2-3 days before the test you should give up even low-alcohol drinks.
Following these simple rules will help you make an accurate diagnosis and avoid repeated visits to the treatment room.
Why is it faster, more convenient and more profitable to take Lab4U tests?
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Prescribing a general blood test is a long-established tradition for the vast majority of doctors of any specialty. A general analysis allows you to estimate the number of formed elements, namely red blood cells, platelets, leukocytes (without subtleties and fractions of various types), hemoglobin level and erythrocyte sedimentation rate (ESR).
The analysis is quite simple, however, this information is enough to suspect an inflammatory process, see anemia, and in some cases, suspect blood cancer or other stem cell pathology.
A complete blood count is a guideline for many subsequent tests and diagnostic procedures, so it is important to do it correctly.
How to take a general blood test correctly
A general blood test should be taken following the doctor’s recommendations
Any blood test, incl. general, it is necessary to take it on an empty stomach, i.e. the period between the analysis and the last meal should be more than 8 hours, but less than 14.
Before this, you should not eat spicy and fatty foods, or overeat - this can affect the ESR. In general, the day before taking a general analysis, it is better to avoid any provoking factors, such as stress, excess physical activity, dehydration or excessive fluid intake (for any reason).
The results of the analysis can be affected by various medications, some of which cannot be canceled (for example, acetylsalicylic acid cannot be canceled for a single day).
Of course general analysis You cannot donate blood while under the influence of toxic or alcoholic intoxication. The same applies to all varieties of hashish, etc. You need to understand that the half-life of the toxin is important. Your well-being cannot be the criterion in this case - at least 48 hours must pass from the moment of intoxication.
General principles of analysis (photo)
Arrive on time 
No smoking 
Don't drink alcohol 
Take on an empty stomach
It is advisable not to smoke an hour before the general analysis, because smoking reduces the number of eosinophils in the general blood pool, i.e. affects the indicator “number of leukocytes”.
You should not take the test “on the run”, i.e. It is advisable to sit and calm down for 15 minutes before the test.
It happens that with full compliance with the above principles, the results are distorted, which becomes clear a little later. This can lead to the fact that the correct diagnosis eludes the doctor for a long time, and the patient will waste time and money searching for a non-existent problem. The second unpleasant moment is the illusion of the absence of a pathological condition, which arose due to a number of factors not taken into account before the analysis.
Factors influencing the results of the analysis
Fear of the procedure greatly affects the results
We will not analyze laboratory errors (this is a separate topic for discussion); we will only describe factors on the part of patients that can lead to an erroneous interpretation of a general blood test.
Fear of doctors, tests, scarifiers. Formed since childhood. Due to the release of adrenaline, cellular elements (primarily red blood cells) leave the blood depot (liver, etc.). As a result, the number of blood cells and the level of hemoglobin in the blood increases, the doctor observes polycythemia and refers the healthy patient to a hematologist. The second option is that a patient with stomach bleeding, for example, due to stress, shows a normal hemoglobin level, he is sent home to “drink vitamins”, after which massive anemia develops with hospitalization and other unpleasant outcomes.
If you are afraid of all these people in white, as well as their scary instruments, warn your doctor about this in advance (or go for tests with your loved ones).
Complete blood count may change in pregnant women
Heavy menstrual bleeding(like any others) can also distort the results of a general blood test. It is advisable to take the test only 4-5 days after their completion.
The time during which the test must be taken must fall between 7:00 and 9:00 (morning). This is due not only to the order of operation of healthcare facilities (which can be overcome if desired), but also to the biorhythms themselves human body. Blood counts can change quite noticeably throughout the day.
If you are taking any painkillers or anti-inflammatory drugs, tell your doctor. Such substances conceal signs of inflammation, therefore (if possible) they are discontinued a week before the expected date of analysis.
Medicines: The influence of drugs on laboratory test results is varied and not always predictable.Meal: possible both direct influence due to the absorption of food components, and indirect - shifts in hormone levels in response to food intake, the influence of sample turbidity associated with increased content fat particles.
Physical and emotional overload: cause hormonal and biochemical changes.
Alcohol: has acute and chronic effects on many metabolic processes.
Smoking: changes the secretion of some biologically active substances.
Physiotherapy, instrumental examinations: may cause temporary changes in some laboratory parameters.
Phase of the menstrual cycle in women: is significant for a number of hormonal studies, before the study you should check with your doctor about the optimal days for taking a sample to determine the level of FSH, LH, prolactin, progesterone, estradiol, 17-OH-progesterone, androstenedione.
Time of day when blood is drawn: there are daily rhythms of human activity and, accordingly, daily fluctuations in many hormonal and biochemical parameters, expressed to a greater or lesser extent for different indicators; reference values - the boundaries of the “norm” - usually reflect statistical data obtained under standard conditions when blood is taken in the morning. 
General rules in preparation for the study: It is advisable to follow these rules when conducting biochemical, hormonal, hematological tests, complex immunological tests; the results depend on the physiological state of the person.
- If possible, it is recommended to donate blood in the morning, between 8 and 11 o’clock, on an empty stomach (at least 8 hours and no more than 14 hours of fasting, drink water, as usual), and avoid food overload the day before.
- If you are taking any medicines, you should consult with your doctor about the advisability of conducting a study while taking medications or the possibility of discontinuing the drug before the study; the duration of withdrawal is determined by the period of removal of the drug from the blood.
- Alcohol – avoid drinking alcohol on the eve of the test.
- Smoking – do not smoke for at least 1 hour before the test.
- Eliminate physical and emotional stress on the eve of the study.
- After arriving at the laboratory, it is recommended to rest (preferably sit) for 10–20 minutes before taking blood samples.
- It is not advisable to donate blood for laboratory research soon after physiotherapeutic procedures, instrumental examination and other medical procedures. After certain medical procedures (such as biopsy prostate gland before a PSA test), laboratory testing should be delayed for several days.
- When monitoring laboratory parameters over time, it is recommended to conduct repeated tests under the same conditions: in the same laboratory, donate blood at the same time of day, etc.
Time of day when taking blood samples for testing - recommendations
Note: “+” - recommended;
“+/-” - allowed with restrictions, the circadian rhythm should be taken into account when studying dynamics and the boundary values of the results relative to the reference limits;
“-” is undesirable.
PREPARATION FOR URINE STUDIES GENERAL RULES:
1. 10–12 hours before the test it is not recommended to consume: alcohol, spicy and salty foods, as well as food products that change the color of urine (beets, carrots).2. If possible, avoid taking diuretics.
3. After cystoscopy, a urine test can be prescribed no earlier than 5–7 days later.
4. Women are not recommended to take a urine test during menstruation.
5. The patient collects urine independently (with the exception of children and seriously ill patients).
6. Before taking the test, perform a thorough toileting of the external genitalia:
- in women, use a cotton swab moistened with warm soapy water to clean the external genitalia (treating the labia by moving the swab in front and downwards); dried with a clean cloth, previously ironed with a hot iron.
- in men - the external opening of the urethra is toileted with warm water and soap, then washed with warm water and dried with a clean napkin, previously ironed with a hot iron.
General urine test
For general analysis, use the first morning portion of urine (the previous urination should be no later than 2 am).Toilet the external genitalia. For men, when urinating, completely pull back the skin fold and release the external opening of the urethra. For women, spread the labia. Pour the first few milliliters of urine into the toilet. Collect the entire portion of morning urine in a dry, clean container while urinating freely. Pour 40–50 milliliters of the total volume of urine into a special container and close the lid tightly. You cannot take urine from a vessel or potty. Collected urine immediately deliver to the laboratory. Urine can be stored in the refrigerator (at +2° +4° C), but not more than 1.5 hours.
24-hour urine collection
Collect urine for 24 hours with normal drinking regimen (1.5–2 liters per day):- at 6–8 o’clock in the morning, empty the bladder (pour out this portion of urine);
- within 24 hours, collect urine in a clean container with a capacity of at least 2 liters; during collection, the container with urine must be stored in a cool place (optimally in the refrigerator on the bottom shelf at t +4° +8°C), preventing it from freezing;
- collect the last portion of urine at exactly the same time the next day when collection began the day before;
- measure the amount of urine, pour 50–100 ml into a clean container. Be sure to write on the container the volume of urine collected per day (daily diuresis).
Urinalysis according to Nechiporenko
Collect urine in the morning (immediately after sleep) using the 3-glass sample method: start urinating in the toilet, collect the middle portion in a container for laboratory testing, and finish in the toilet.The second portion of urine should prevail in volume. Deliver a medium portion of urine to the laboratory. Report the time of urine collection to the registrar. It is allowed to store urine in the refrigerator (at t +2° +4°), but not more than 1.5 hours.
Urine analysis according to Zimnitsky
Collect urine for 24 hours at the usual drinking rate (1.5–2 liters per day), taking into account the amount of liquid drunk per day.At 6 o'clock in the morning, empty your bladder (pour out this portion of urine).
Every 3 hours during the day, collect urine in separate containers, which indicate the time of collection and the portion number.
Total 8 servings:
- 1 serving – from 6-00 to 9-00,
- 2 servings – from 9–00 to 12–00,
- 3 servings – from 12–00 to 15–00,
- 4 servings – from 15–00 to 18–00,
- 5th portion – from 18–00 to 21–00,
- 6 portion – from 21–00 to 24–00,
- 7 portion – from 24–00 to 3–00,
- 8th portion – from 3-00 to 6-00.
Deliver the entire collected amount of urine in 8 containers to the laboratory.
Taking any tests will be as comfortable as possible for you. The analysis is carried out using expert-class diagnostic instruments.
Blood test: what affects the result
The list of blood tests is huge: general analysis (hemogram), biochemistry, studies of hormones, tumor markers, hemostasis, immunological studies, molecular genetic and a number of others.
The research results are influenced by:
- Medicines.
- Food: direct effect due to the absorption of food components, indirect effect due to a shift in hormone levels.
- Physical or emotional overload: they cause hormonal as well as biochemical changes.
- Physiotherapy, instrumental examinations: they cause a temporary change in a number of laboratory parameters.
- Alcohol: acutely affects a number of metabolic processes.
- Smoking: changes the secretion of a number of biologically active substances.
- The phase of the menstrual cycle: is significant for many hormonal studies, and before the study you should check with a clinic specialist on the optimal days for taking tests (FSH, LH, estradiol, prolactin, progesterone, 17-OH-progesterone and others).
- Time of day: the daily rhythms of the body’s activity are known and, therefore, daily fluctuations in biochemical and hormonal parameters are known (the boundaries of the “norm” usually reflect statistical data obtained when donating blood in the morning).
You need to talk about all of the listed “agents of influence” with the clinic’s doctor.
Features of blood tests
Clinic professionals can always tell you about the rules for proper preparation for any tests.
- For most tests, you need to donate blood on an empty stomach, after 8 a.m. and before 11 p.m. The analysis is taken 8 hours (or more) after a meal (evening). Drink water as usual.
- For a biochemical blood test, you need to follow a diet for a couple of days: do not eat foods rich in purines (liver, kidneys), limit meat, fish, tea, coffee to the maximum. You need to give up sports and intense physical activity.
- There are tests for which blood is donated on an empty stomach and after 12-13 hours of fasting. These are tests for gastrin-17, total cholesterol, a number of lipid profile tests, as well as a glucose tolerance test (with this test, you cannot brush your teeth in the morning, or even drink unsweetened tea or coffee. Contraceptives, diuretics, and a number of other medications also have an effect).
- Blood for hormonal studies is donated on an empty stomach in the morning. A day or two before the tests, foods high in fat are excluded. Do not overheat or overcool. Thyroid hormones: two to four weeks before the test, medications that affect the functioning of the thyroid gland are discontinued. Of course, this is discussed with the doctor. Sex hormones: in women, such tests are taken strictly according to the days of the menstrual cycle.
- A day before any analysis, alcohol, sports, powerful physical and emotional stress are excluded.
- You must discuss the possibility of taking medications with your doctor.
- Before the analysis (two hours), smoking, juice, tea, and coffee are excluded.
- Some studies require additional restrictions. The doctor at our clinic will tell you about them.
Urine examination: preparation
Various urine tests also have their own limitations and rules.
- Before taking the test, do not consume (12 hours before): alcohol, salty and spicy foods, foods that affect the color of urine (carrots and beets).
- If possible, remove diuretic medications.
- Women should not get tested during their period.
- Immediately before the test, the genitals are toileted.
- To submit a general analysis to the clinic, the first morning urine is taken. The first few milliliters need to be flushed down the toilet. Collect the entire portion in a clean container, pour approximately 50 milliliters into a special container, close tightly.
There are tests when daily urine is taken, tests using the methods of Nechiporenko, Zimnitsky, urine biochemistry, hormone testing, microbiological testing, testing for bladder cancer antigen. Each type has its own rules.
Modern equipment, latest technologies allow our clinic specialists to conduct any type of analysis quickly, accurately, and affordably. Trust your health to professionals.
Read also
Pregnancy test
The future placenta, from the very first day of its existence, secretes a specific human chorionic hormone (hCG), which blocks the function of the ovaries to produce the next egg, thereby preventing a secondary pregnancy. It is on the detection of this chorionic hormone that the principles of early diagnosis of pregnancy are based. HCG is produced from the first day of pregnancy, but tests are calculated on a certain level of hubbub, and therefore it is possible to reliably determine pregnancy using a test starting from approximately two weeks, i.e. with a delay in menstruation.
