Inaccurate Blood Test Versus Lifesaving Screening Tool
– By William M. Figlesthaler, M.D. –
Prostate cancer screening has received a great deal of press over the past decade or two. The introduction of the prostate specific antigen blood test (PSA) in the late ’80s has resulted in a significant number of prostate cancers being diagnosed at early clinical stages. In fact, each year over 200,000 cases of prostate cancer are diagnosed in the United States alone and over 30,000 men die of this disease annually.
Early Diagnosis is Key
Early diagnosis is a key ingredient to successful cure rates with decreased morbidity. Current knowledge on how to use PSA values to determine which men need urological evaluation is vitally important to primary care providers, especially when dealing with healthy males between the ages of 40 and 80 years of age.
It was once considered standard of care to interpret any PSA reading between zero and 4.0ng/dl as normal. Fluctuations within this range were given little if any significance. In addition, levels as high as 6.5ng/dl were even considered acceptable in men over the age of 70 at one time. Using these parameters was successful in minimizing the “over diagnosis” of prostate cancer in elderly males with clinically insignificant prostate cancers. Unfortunately, many younger patients with more aggressive cancers were left undiagnosed until they had non-organ-confined disease, which negatively impacts cure rates as well as morbidity of treatment.
In addition to the total PSA blood test, free PSA testing may be used to increase the specificity of a borderline or high PSA result (4-10ng/dl). Free PSA is reported as a percentage of the total PSA, and represents the fraction of serum PSA that is unbound to a carrier protein. Patients with prostate cancer have less free PSA.
Guidelines for Interpreting PSA Values in the Screening for Prostate Cancer
The following guidelines represent the current standard for interpreting PSA values in the screening of men for prostate cancer. It is important to include in this discussion the necessity of the digital rectal exam which if abnormal must be evaluated, regardless of the PSA result:
- PSA levels over 2.0ng/dl in males under the age of 50 and PSA levels over 2.5ng/dl in males under the age of 60 should be considered abnormal.
- PSA levels over 4.0 ng/dl should always be considered abnormal and warrant urological evaluation.
- An increase in PSA (PSA velocity) of 0.7ng/dl over an 18-month time span should be considered significant, even if within the normal range for PSA (0-4ng/dl).
- Free PSA levels below 10% indicate a significant risk for prostate cancer.
- PSA levels should be considered inaccurate if obtained in the presence of a urinary tract infection, prostatitis or after a traumatic foley catheter placement. A period of four to six weeks after treatment should be sufficient to allow the PSA to return to baseline.
- 5-a-reductase inhibitors such as Proscar or Avodart lower the PSA by 50% over a six-month period of time, and discontinuing these medications will result in the return to the baseline PSA reading over a similar time frame. Therefore, a patient who is started on Avodart, takes it as directed and then has a similar PSA reading a year later should be referred for urological evaluation and possible prostate biopsy. It is important to question patients who are prescribed these medications regarding treatment compliance when interpreting their PSA values.
PSA Blood Test is a Valuable Adjunct to Digital Rectal Exam
In summary, the PSA blood test is a valuable adjunct to the annual digital rectal examination. In order to maximize the benefit of PSA, it is essential to properly interpret the result as it relates to the patient’s age, velocity of change and other factors, which could alter the PSA value such as infection, trauma or medications. The primary care provider is the first responder when it comes to determining when a patient may be at an elevated risk for prostate cancer based upon annual screening. Both the digital rectal exam and the PSA blood test are necessary to properly screen male patients for prostate cancer. Urological referral should be considered whenever there is a question of an abnormal PSA or digital rectal examination.
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