Blood and urine laboratory tests are necessary to diagnose the state of the patient. These tests are also helpful in the assessment of diet and nutritional status of the organism. It is recommended that both blood and urine for laboratory tests be collected in the morning, from fasting patients after an overnight rest. These conditions are defined as the standard conditions for collection of material for laboratory testing. Before testing, patients should follow their natural diet and avoid physical exertion, night work, long-distance travel, as well as consumption of alcohol and drugs. They should also reduce the consumption of synthetic vitamins and herbal remedies and other dietary supplements. Medications should be limited to those that are absolutely necessary. All of these factors can affect the results of laboratory tests.