Prostate Specific Antigen
Prostate Specific Antigen (PSA), is a protein secreted by the acinar cells of the Prostate, and is highly specific for the Prostate. Serum PSA levels are useful for determining the extent of Prostate Cancer, and assessing the response to therapy. However, it is NOT Prostate cancer specific and other conditions such as: Benign Prostatic hyperplasia (BPH) or Prostatitis can affect PSA levels.
- PSA is commonly used as a tool to detect Prostate Cancer, but its role in screening programmes is widely debated and controversial.
Clinical utility:
PSA has a half-life of 2.2 days. Where levels are increased by different Benign conditions, the time to return to baseline levels is variable.
The common causes of an elevated PSA are:
A) Perineal trauma:
Mechanical manipulation of the Prostate during biopsy or transurethral resection of the Prostate (TURP) can significantly affect PSA. In a study of 101 men who underwent one of these procedures, it was determined that PSA levels should not be measured for at least 6 weeks thereafter. In the same study, the median change in PSA level was of a lesser magnitude following Cystoscopy.
- Digital Rectal Examination (DRE) has minimal effect on PSA levels. (Leading to transient elevations of 0.26 – 0.4 ng/ml).
- Sexual activity can also elevate PSA levels by approximately 0.4 - 0.5 ng/ml.
B) Infection and inflammation:
- Prostatitis, with or without active infection, is an important cause of an elevated PSA. Levels as high as 75 ng/ml have been reported. Many physicians will make a presumed diagnosis of infection, initially treating a patient with an isolated increase in PSA with antibiotics and repeating the PSA measurement afterwards.
- A reduction in PSA levels can be expected if prostatitis with infection was solely responsible for the elevation. However, prostatitis can often exist without active infection, in which case the PSA will not normalise after treatment with antibiotics. Serum PSA should only be repeated about 2 - 4 weeks after completion of treatment for reassessment.
C) Benign Prostatic hyperplasia:
There is a high prevalence of this condition in men older than 50 years of age, and serum PSA levels in patients with BPH overlap considerably with those obtained from men who have Prostate cancer.