What is it?

Laboratory test samples are analyzed to determine whether the test results fall within normal ranges. They also may be checked for changes from previous tests. Normal test values are usually given as a range, rather than as a specific number, because normal values vary from person to person. What is normal for one person may not be normal for another person. Many factors (including the patient's sex, age, race, medical history and general health) can affect test results. Other factors that sometimes affect test results include specific foods, drugs the patient is taking, how closely the patient follows preparatory instructions, and variations in laboratory techniques. It also is common for normal ranges to vary somewhat from laboratory to laboratory.