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Laboratory tests go through three stages from sample collection to result reporting. The pre-analytical stage, which occurs before sample collection, is the phase that should be under the control of the laboratory. It involves selecting, ordering, appropriately collecting samples for analysis, processing, transporting, and preparing samples according to the patient’s clinical condition. The process always begins with the patient and ends with the patient. The pre-analytical stage can be classified based on factors related to the patient, sample, and specimen, or it can be divided into periods such as before, during, and after sample collection.


Factors Affecting Laboratory Tests

Effect of Posture: The blood volume of a normal adult in the standing position is 600-700 ml (a 10% decrease) less than that of a person lying down. This results in a significant difference in plasma volume because proteins will pass through capillaries in an upright posture. As a result, the concentration of all proteins will increase (enzymes, hormones in protein structure, drugs carried by proteins, calcium, and bilirubin). During a few days of bed rest, plasma and extracellular fluid volume decrease, leading to a 10% increase in hematocrit. Prolonged bed rest leads to fluid retention, resulting in a decrease in protein and albumin levels. Increased ionized calcium levels occur due to mobilization of bone calcium.


Effect of Exercise: The effect of exercise on body fluids depends on the duration and intensity of the activity. After exercise, blood samples show elevations in aspartate aminotransferase (AST), lactate dehydrogenase (LDH), creatine kinase (CK), urea, creatinine, and transferrin levels. Changes in plasma renin activity, aldosterone, and growth hormone reaching pathological levels should be considered. Hematuria and proteinuria may occur. To minimize the impact of exercise as a pre-analytical variable, it is recommended not to engage in strenuous sports, long-distance walking, or running a day before blood donation. Exercise can also cause changes in some hormones.


Fasting Status: Generally, a fasting period of 10-12 hours is required for laboratory tests. A fasting period longer than 16 hours is not preferred.


Effect of Foods: The effect of certain plasma components can vary with the foods consumed during a meal. The most significant increases occur in serum glucose, iron, total lipids, and alkaline phosphatase levels. Caffeine-containing beverages such as coffee, tea, and cola affect the concentration of blood components.


Smoking: Smoking affects many laboratory tests due to the nicotine it contains. These include lipids, hormones, vitamin B12, and CEA. Glucose tolerance is also impaired in smokers.


Alcohol Consumption: Short and long-term effects of alcohol consumption can cause changes in various analytes. Short-term effects of ethanol intake 2-4 hours after intake reduce plasma glucose levels and increase uric acid and lactate levels. Long-term use causes an increase in GGT, AST, and ALT levels. Hypertriglyceridemia is observed after alcohol consumption.


Medication Use: Medications have both in vivo and in vitro effects on laboratory tests. When administered intramuscularly, drugs can cause muscle irritation, leading to an increase in some enzymes (such as creatine kinase, aldolase, and lactate dehydrogenase).


Fever: Fever affects many parameters, including serum hormone levels, lipids, calcium levels, and uric acid.


Effect of Age and Gender: Although there are generally reference values for children, adolescents, adults, and the elderly for laboratory tests, there are significantly different reference values, especially for the neonatal period. For example, alkaline phosphatase reaches its highest levels during puberty, parallel to bone growth. Activity decreases after puberty. Structural differences between males and females lead to very different reference values in many biochemical and hematological tests, especially in endocrine tests.


Pregnancy: Although pregnancy is a physiological condition, the changes that occur in the organism affect many laboratory parameters. The most important change in pregnancy is hemo-dilution due to an increase in average plasma volume. This should be considered in the interpretation of all laboratory test results.


Diurnal Rhythm: Changes in the secretion, metabolism, or circulation of some analytes can be observed throughout the day. For example, serum iron may vary between two different times of the same patient around 08:00-14:00. Serum cortisol levels peak around 06:00 in the morning and reach their lowest levels around 00:00 at night. Also, glucose values in glucose tolerance tests performed in the afternoon may be slightly higher than those performed in the morning.


Seasonal Changes: Especially between the summer and winter seasons, some laboratory parameters may differ. These include higher vitamin D levels in summer.


Altitude: Living at higher altitudes than sea level affects some laboratory parameters. High levels are observed in tests such as hemoglobin, hematocrit, and CRP.

To start collecting a 24-hour urine sample, empty your bladder into the toilet immediately upon waking up and note the time (e.g., 8:00 in the morning). From this point on, collect all your urine carefully in the collection container throughout the day and night (without missing a single drop). After collecting the first urine of the next morning (e.g., your urine at 8:00 the next morning), add it to the collection container to complete the urine collection process. Bring it to the laboratory without waiting. During urine collection, keep your collection container protected from the sun and in a cool environment. You can obtain your 24-hour urine collection container from our laboratory.

If a protective substance was given to you during urine collection: These substances are corrosive! Keep them out of reach of children. If it comes into contact with your skin, wash it immediately with plenty of water. Open it carefully and empty it slowly into the collection container. Stir the entire urine with each addition. If the first urine collection container is full, when you switch to another urine collection container, mix about half of the urine in the previous container into this one.

Sample Collection



The collection method, urine containers, and storage conditions are crucial in the collection and transportation of urine samples to the laboratory, as these variables can significantly impact analysis results, guiding diagnostic and treatment decisions.


Urine samples should not be collected in bottles, plastic cups, or similar containers. They should always be collected in sterile containers obtained from the laboratory.


Midstream urine is the recommended collection method for urine bacterial culture. All necessary materials for genital hygiene are provided by the laboratory staff. After the cleanliness process, a portion of urine is collected in the provided container after voiding a small amount of urine externally.


The sample should be delivered to the laboratory as soon as possible.


Samples should not be collected from patients with catheters at home. Our laboratory staff will assist you in the sample collection process.


For tuberculosis culture requests, the suitable sample is the morning’s first urine collected on three consecutive days.




Sputum samples are often requested to identify respiratory pathogens. Similar to urine, sputum samples should not be collected in bottles, plastic cups, or similar containers; they should always be collected in sterile containers obtained from the laboratory.


After rinsing your mouth with water, expectorate sputum into a sterile container with a strong cough. There should be no saliva or postnasal drip with the sample.


For tuberculosis culture requests, the suitable sample is the morning sputum sample collected on three consecutive days.




Fecal samples are commonly used to find viral/bacterial causes of diarrhea, search for parasites and parasite eggs, and detect gastrointestinal system bleeding (hidden blood).


  • Collection for Culture
  • Collecting the fecal sample
  • The patient collects the sample in a container provided by the laboratory.
  • After placing the stool in a dry container, it can be transferred to a screw-capped transfer container using a plastic or wooden spoon.
  • Toilet paper should not be used for sample collection.
  • For babies, an inverted (with the plastic side inside) diaper should be used to prevent the diaper from absorbing the stool.
  • Considerations during sample collection
  • Urine should not mix with feces under any circumstances.
  • Samples should be taken from mucous, purulent, and bloody parts of the stool.
  • A walnut-sized (1-2 g) stool is sufficient for fecal examinations.
  • After collecting the stool, it should be sent to the laboratory as soon as possible (within 1 hour).
  • Collection for Parasite Examination
  • For the detection of parasites and parasite eggs, it is preferred to collect samples on three consecutive days and send them to the laboratory.
  • The sample should be fresh and not dried, especially for samples where amoebas are to be searched; they should be in the laboratory within half an hour.
  • Before sampling, it should not be exposed to contrast agents used in radiology.
  • Enterobius vermicularis examination (Cellophane tape method)

Since pinworms lay eggs around the anus early in the morning, a sample taken from this area using the cellophane tape method is attached to a slide and sent to the laboratory. Detailed information on this can be provided by laboratory personnel.


Collection for Hidden Blood in Stool

Samples can be sent to the laboratory in a sample container, or after applying the stool to test cards provided by the laboratory, they can be sent back for testing for hidden blood.

Blood Donation

In our country, the habit of blood donation is not well-established, leading to a shortage of blood and blood products. Therefore, in our hospital, we strive to obtain the necessary blood for patients with urgent blood needs, those undergoing surgery, or those with chronic blood diseases who require continuous blood transfusions, by utilizing the blood donations from their relatives or individuals in our community who show sensitivity to blood donation. Blood donation is entirely based on voluntarism, and no one can force another person to donate blood!

Before donating blood, please check your eligibility for it!

Who can donate blood?

  • Women and men between the ages of 18-60,
  • Individuals weighing over 50 kg,Those without blood pressure problems,
  • Should not have a fever,
  • Those without detected anemia,
  • Those whose last donation date is at least three months ago.
  • Who cannot donate blood under any circumstances?
  • Those who test positive for HBsAg, HCV, anti-HIV, or VDRL,
  • Heart patients,
  • Individuals with asthma and allergies,
  • Epilepsy patients (those with epilepsy),
  • Those with high blood pressure,
  • Those using continuous medication,
  • Pregnant women,
  • Individuals with immunodeficiency who are first-degree relatives of patients.

Before donating blood, the eligibility of voluntary donors is checked for their well-being. Therefore, a tube of blood is first drawn for a blood count, and blood pressure and pulse are checked. If these are suitable, the person donating blood is asked to fill out the background questionnaire form correctly.

Your blood will be tested for diseases such as hepatitis B and C, AIDS, and syphilis. During the blood donation process, a separate sterile needle and blood set are used for each person.

The questions on the “Donor Inquiry Form” are designed to protect the blood donor and the person receiving the blood. Remember that the blood you give can be given to an innocent patient or a newborn baby who has no chance of rejecting the blood, and it may carry diseases such as AIDS virus. Even if you feel well, you could transmit this virus. If you still have doubts about donating blood when you fill out the form, you can leave the Blood Donation Station without explaining to anyone or speak privately with the responsible person at the Blood Donation Station.

Department Doctors


Spec. Dr. İhsan AYTURAN

Biochemistry Specialist