Depending upon prescribed test, as some tests are designed to measure the effect of drugs and prevent toxicities from too high a level. Those tests should be done using blood specimens collected at precise times, such as just before the next dose, to make the right interpretation.

White cell counts are slightly higher for smoker than non-smokers because of irritation to the lungs and probably to blood vessels too. Smokers also have higher levels of carbon monoxide. With chronic lung disease from smoking, oxygen levels fall in the blood, and carbon dioxide rises. Elevation of enzymes in the blood from the liver is caused if for mild drinking, which can be confused with early stage hepatitis. Alcoholics are at risk to develop serious liver disease such as cirrhosis, which produces marked abnormalities in many laboratory tests (e.g., bilirubin, AST, ALT, LDH, albumin, and others).

A few endocrine tests (especially cortisol from the adrenal cortex) are strongly influenced by time of day, which should be specified by the ordering physician. Some tests are best done after 12 hrs fasting (cholesterol, triglycerides, and other lipids).

All lab test results are reported with a normal range that is expected in good health. If the numerical result is outside that range, it may indicate illness or organ damage that requires medical treatment. The more out-of-range the results, the more likely it is to be a serious change.

Depends upon the Physician and kind of test prescribed. Mild abnormalities may lead a physician to repeat a test on the next visit or to order a confirmatory test that makes a diagnosis more certain. If the result is normal, it may not be necessary to re-test for a few years if the patient feels well.

Laboratory measurements have become highly reliable due to advances in instrumentation. However, the quality of the specimen (How well was it collected? How was it stored and handled before testing?) may lead to abnormal results that should be re-tested before embarking on a new course of treatment. We always suggest patients to go directly to Laboratory for blood testing to avoid / minimize pre-testing error.

There are many factors minor and major which can effect the quality of report. Preparation taken by patient before sample collection to serum extraction and then quality of reagents and equipments used for testing. Day to day standardization of equipments also plays a vital role in giving accurate report.

The body metabolism goes through cycles every time food is eaten. Glucose rises in the blood, phosphates fall, lipids rise, etc. Accurate timing of blood collection around meals is very important for some diagnostic tests. These include glucose and lipids. Some other tests are not affected much by eating and can be collected in the morning or in the afternoon after lunch. These include blood cell counts, coagulation tests, many tests for kidney and liver function, and most common blood chemistry tests.