PSA is also known as Prostate Specific Antigen is a marker for Prostate Cancer. Although there is no consensus about using the PSA test to screen for prostate cancer in asymptomatic men however it is routinely used along with digital rectal exam for the same, The total PSA test may be used as a monitoring tool to help determine the effectiveness of treatment. and to detect recurrence of the cancer. If either the PSA or the DRE are found to be abnormal, then the doctor may choose to follow this testing with a prostate biopsy and perhaps imaging tests, such as an ultrasound. If the DRE is normal but the PSA is moderately elevated, the doctor may order a free PSA test to look at the ratio of free to total PSA. This can help to distinguish between prostate cancer and other non-cancer causes of elevated PSA. Since the total PSA test can be elevated temporarily for a variety of reasons, a doctor may order another PSA a few weeks after the first to determine if the PSA is still elevated. PSA test results can be interpreted a number of different ways and there may be differences in cutoff values between different laboratories. The normal value for total PSA is considered to be less than 4.0 ng/ml (nanograms per milliliter of blood). There are some that feel that this level should be lowered to 2.5 ng/ml in order to detect more cases of prostate cancer. Others argue that this would exacerbate over-diagnosing and over-treating cancers that are not clinically significant. There is agreement that men with a total PSA level greater than 10.0 ng/ml are at an increased risk for prostate cancer (more than a 67% chance,). Levels between 4.0 ng/ml and 10.0 ng/ml may indicate prostate cancer (about a 25% chance), BPH, or prostatitis. These conditions are more common in the elderly, as is a general increase in PSA levels. Concentrations of total PSA between 4.0 ng/ml and 10.0 ng/ml are often referred to as the "gray zone." It is in this range that the free PSA is the most useful. When men in the gray zone have decreased levels of free PSA, they have a higher probability of prostate cancer; when they have elevated levels of free PSA, the risk is diminished. The ratio of free to total PSA can help the doctor decide whether or not a prostate biopsy should be performed. During treatment for prostate cancer, the PSA level should begin to fall. At the end of treatment, it should be at very low or undetectable levels in the blood. If concentrations do not fall to very low levels, then the treatment has not been fully effective. Following treatment, the PSA test is performed at regular intervals to monitor the person for cancer recurrence. Since even tiny increases can be significant, those affected may want to have their monitoring PSA tests done by the same laboratory each time so that testing variation is kept to a minimum. Since the DRE can cause a temporary elevation in PSA, the blood is usually collected prior to performing the DRE. Prostate manipulation by biopsy or resection of the prostate will significantly elevate PSA levels. The blood test should be done before surgery or six weeks after manipulation. Rigorous physical activity affecting the prostate, such as bicycle riding, may cause a temporary rise in PSA levels. Ejaculation within 24 hours of testing can be associated with elevated PSA levels and should be avoided. Large doses of some chemotherapeutic drugs, such as cyclophosphamide and methotrexate, may increase or decrease PSA levels. In some men, PSA may rise temporarily due to other prostate conditions, especially infection. A recent study found that in about half of men with a high PSA, values later return to normal. Some authorities recommend that a high PSA should be repeated, between 6 weeks and 3 months after the high PSA, before taking any further action. Some physicians will prescribe a course of antibiotics if there is evidence that there is infection of the prostate.