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Serum PSA test and it’s significance

PSA or prostate specific antigen is a protein that is produced by normal as well as cancerous prostate 

gland. Normally a small quantity of PSA is secreted by prostate gland but abnormal levels are produced in prostate cancer. Testing PSA levels are widely used as screening test for prostate cancer. Though it is an excellent test to detect cancer prostate many noncancerous conditions also may produce high levels of PSA. A large benign ( non cancerous prostate ), prostate inflammation or so called prostatitis , urinary tract infection may elevate PSA levels even to a very high level. Sexual intercourse and ejaculation, rectal examination of prostate, trans rectal sonography, cystoscopy and prostate biopsy and prostate surgery ( TUR P ) also elevate PSA level in blood.

Long term usage of dutasteride / finasteride ( Dutas/ Finast ) may lower PSA level. So high PSA level interpretation needs careful consideration of all relevant factors.

It is widely accepted that PSA level less than 4 ng/ml is considered as normal. Above 10 ng/ml arises suspicions about cancer. Between 4 to 10 ng/ml is considered equivocal. But patient may have cancer even with normal values and high level of PSA may not have cancer. it’s better to measure free PSA level simultaneously. If free PSA is more than 25% of total PSA then prostate cancer is unlikely. If free PSA is 10% or less than total PSA then prostate cancer is more likely. Highly suspicious levels should be biopsied after a contrast MRI.

As prostate cancer is a disease of elderly and early diagnosis of prostate cancer helps patient to get a cure ( either by surgery or radiation ). PSA testing with all its shortcomings should be advocated for all males above the age of 50 years. But if there is family history of prostate cancer then screening should start from the age of 40 years.

Limitations of PSA testing : test result may be false positive ( high PSA – but no cancer ) or false negative ( low PSA – but cancer present ). Sometimes a small and slow growing tumour is detected that may not necessarily result in death from prostate cancer. This often result in over diagnosis and over treatment. Over treatment result in unnecessary complications and side effects of cancer treatment. So one have to be very careful and judicious in treatment selection.

PSA testing is helpful in detecting cancer recurrence following treatment. But a single rise in PSA level may not be that indicative of recurrence; serial measurement and rise would be more significant

PSA DOUBLING TIME : rapid doubling time may indicate presence of cancer 
PRO PSA : pro PSA is more strongly associated with prostate cancer then non cancerous enlargement
ISO PSA : PSA exists in many isoforms. Measuring isoforms rather than total PSA may help In detecting prostate cancer better.
PSA AND BIOMARKERS : Measuring PSA along with various biomarkers associated with prostate cancer may be an excellent screening tool in future.

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