What affects test results: 7 factors that change the picture of health

Why test results may be inaccurate

Have you ever had a blood or urine test and then had it repeated and received a completely different result? In most cases, it's not a lab error, but influence of external and internal factors, which change the indicators. Even a cup of coffee or stress before the procedure can distort the data.

Understanding, What exactly affects the test results?, helps to obtain accurate information about the condition of the body and avoid unnecessary diagnoses or incorrect treatment.

The main factors that change the results of laboratory tests

1. Food and drinks before tests
   Even a light breakfast before donating blood can increase glucose, cholesterol, and iron levels. Coffee, juices, and sweet tea activate metabolism and affect liver enzymes. Therefore, most tests should be taken on an empty stomach — at least 8–12 hours after eating.

2. Physical activity the day before
   Intense exercise or even climbing stairs before the test can increase the levels of creatine phosphokinase (CPK), lactate, and leukocytes. If the goal is to assess the general condition of the body at rest, it is important avoid physical exertion 24 hours before the test.

3. Stress, lack of sleep and emotional stress
   The psycho-emotional state directly affects the level of hormones: cortisol, adrenaline, prolactin, as well as glucose and blood pressure. For the hormonal profile it is important to rest, get some sleep and come to a state of calm.

4. Medications and dietary supplements
   Even vitamins or herbal supplements can change the results. For example, taking iron will increase its level in the blood, diuretics affect electrolytes, antibiotics - on microflora indicators. Be sure to inform your doctor or laboratory technician about all the medications you take.

5. Time of day
   Some hormones (e.g. cortisol, testosterone, TSH) have a clear circadian rhythm. Their levels change throughout the day, so it is important to adhere to the recommended time of delivery — usually by 10:00 am.

6. Smoking and alcohol
   Nicotine activates the cardiovascular system, while alcohol disrupts liver enzymes and clotting parameters. Give up alcohol for 48 hours, and from smoking - at least 2 hours before the analysis.

7. Physiological states: menstruation, pregnancy, lactation
   Hormonal changes during these periods affect the results of blood tests, urine tests, and coagulation tests. For example, pregnant women experience changes in hemoglobin, ESR, and albumin levels. Mandatory inform the medical staff about your condition.

Table: How different factors affect popular analyses

How to prepare for accurate results

• do not eat for 8–12 hours before blood collection

• do not smoke for at least 2 hours before the analysis

• avoid physical exertion and stress

• report taking medications or dietary supplements

• take the tests in the morning, preferably at the same time

• for women - if possible, avoid blood sampling during menstruation (unless required by indications)

References to sources

1. WHO – Manual of basic techniques for a health laboratory

2. Mayo Clinic – Lab test preparation: What you need to know

3. FDA – Laboratory test interpretation and patient preparation

Knowing what affects test results will not only help maintain accuracy, but also avoid retesting and false alarms. Proper preparation is part of your responsibility for your own health.