Laboratory tests a sample of your blood, urine, or body tissues. your doctor analyzes the test samples to see if your results fall within the normal range. The tests use a range because what is normal differs from person to person. Many factors affect test results. These include:

• Your sex, age and race
• What you eat and drink
• Medicines you take
• How well you followed pre-test instructions

Your doctor may also compare your results to results from previous tests. Laboratory tests are often part of a routine checkup to look for changes in your health. They also help doctors diagnose medical conditions, plan or evaluate treatments, and monitor diseases.