Laboratories perform tests on blood samples and measure the results against accepted ranges. Results are used to diagnose illness, measure medication levels, help employers make hiring decisions and indicate the presence of drugs and alcohol for legal purposes. Certain supplements, such as vitamins and minerals, may affect blood test results by causing false positives or false negatives. Your doctor can provide information about supplements and their influence on blood testing.
Medical professionals and laboratories follow strict procedures to draw and test blood samples. Each effort helps ensure that blood test results are correct. False test results occur because of errors or because specific substances, such as supplements, corrupt the test results. A false negative test result rules out the condition or substance when it actually exists. A false positive says that the condition or substance is present when it is not. Inaccurate test results can cause patients to undergo unnecessary tests and procedures or delay treatment for a serious condition.
A blood test used for early detection of prostate cancer measures the amount of prostate-specific antigen, or PSA, in the blood. High levels of PSA may indicate the presence of prostate cancer. Supplements made of herbal mixtures can mask the high PSA levels that might indicate the presence of prostate cancer. If you are undergoing this test, let your doctor know about any supplements you are taking.
Hormone supplements taken by women can affect the results of a blood test used to measure the amount of human chorionic gonadotropin, or HCG, in the blood. The body produces the HCG hormone during pregnancy. Hormone supplements can cause the test results to show a false positive by indicating a pregnancy when there isn't one.
Very high doses of vitamin C supplements can elevate blood sugar levels and, because of blood glucose test results, indicate Type 2 diabetes when the patient does not have the condition. People with diabetes show high levels of glucose in their blood, which indicates the body’s inability to move glucose from the blood to the cells. Vitamin C supplements also interfere with a true diabetic’s glucose monitoring, which is necessary to manage the disease and control blood sugar levels.