Screening tests are those that are done at regular intervals to detect a disease such as prostate cancer at an early stage. If the result of a screening test is normal, the disease is presumed not to be present. If a screening test is abnormal, the disease is then suspected to be present, and further tests usually are needed to confirm the suspicion (that is, to make the diagnosis definitively). Prostate cancer usually is suspected initially because of an abnormality of one or both of the two screening tests that are used to detect prostate cancer. These screening tests are a digital rectal examination and a blood test called the prostate specific antigen (PSA).
In the digital rectal examination, the doctor feels (palpates) the prostate gland with his gloved index finger in the rectum to detect abnormalities of the gland. Thus, a lump, irregularity, or hardness felt on the surface of the gland is a finding that is suspicious for prostate cancer. Accordingly, doctors usually recommend doing a digital rectal examination in men age 40 and over.
The PSA test is a simple, reproducible, and relatively accurate blood test. It is used to detect a protein (the prostate specific antigen) that is released from the prostate gland into the blood. The PSA level is usually higher than 4ng/mL in people with prostate cancer than in people without the cancer. Situations of large prostate size, infection and inflammation are other reasons why the PSA may be elevated. The PSA, therefore, is valuable as a screening test for prostate cancer. Accordingly, doctors usually recommend doing a PSA in men age 40 and over. Subsequent screening is recommended based on individual preference and assessment of risk for developing prostate cancer. For example, patients with a high risk of developing prostate cancer due to a family history or a high initial PSA should have more frequent evaluation (usually annually).
Although, still considered controversial, most urologists recommend regular screening for prostate cancer in men who are likely to live for more than 10 years. The American Urological Association (AUA) issued their latest guidelines for prostate cancer in 2009. According to these, men at the age of 40 should be offered a baseline PSA test and a prostate exam (digital rectal exam or DRE) to ascertain the risk of prostate cancer. Subsequent screening and tests may be performed according to the findings on this initial evaluation and an individual's risk of getting the disease on the basis of other factors such as race, ethnicity, and family history of prostate cancer. As mentioned, most urologists currently would advise some form of screening in men with a life expectancy greater than 10 years. Most frequently, it would be performed on an annual basis. Although, there is no definite cutoff age to stop prostate cancer screening, most physicians would rarely screen men more than 75 years of age for this disease.
Results of the PSA test under 4 nanograms per milliliter of blood are generally considered normal. There is a recent trend, however, to perform prostate biopsy in all patients with a PSA more than 2.5 ng/ml in order to detect prostate cancer at an earlier (and hopefully, completely curable) stage. The American Urological Association guidelines (2009) do not define a definite cutoff point but advise that all the other risk factors for prostate cancer should be taken into account while making a decision on whether to proceed for a biopsy. One of the important factors that needs to be considered is the rate at which the PSA value has increased over time on repeated measurements (PSA velocity). Results between 4 and 10 are considered borderline. These borderline values are interpreted in the context of the patient's age, symptoms, signs, family history, and changes in the PSA levels over time. Results higher than 10 are considered abnormal, suggesting the possibility of prostate cancer. It has been shown that the higher the PSA value, the more likely the diagnosis of prostate cancer. Moreover, the level of PSA tends to increase when the cancer has progressed from organ-confined prostate cancer to local spread to distant (metastatic) spread. Very high values, such as 30 or 40 and over, are usually caused by prostate cancer.
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Archived: March 20, 2014
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