<prompt> Mr. Chaturvedi a 70 year old man comes to casualty with urinary retention and back pain. Which investigation should be performed ?Serum acid phosphataseSerum CalciumSerum alkaline phosphataseSerum electrophoresis  <response>: Ans. is a Serum acid phosphatse This pt. is suspected to have Ca Prostate as Prostatic Ca is the most common malignant tumor in men over 65 yrs. of age. Symptoms of Bladder outlet obstruction and back pains due to bony metastasis in the pelvis lumbar veebra indicate towards prostate Ca. Serum acid phosphatase is a tumor marker of prostate Ca. But now serum acid phosphatase assay has been superseeded by PSA assay Prostate specific antigen. Prostate specific antigen It is a glycoprotein produced only in the prostatic cells both benign malignant. It facilitates liquefaction of semen. It is neither sensitive nor specific for early prostate carcinoma it is prostate specific and not prostate cancer specific, neveheless it gives some help in making a diagnosis. Normal serum level --- less than 4 ngml 4 - 10 ngml --- this range is common for both BHP and Ca. More than 10 ngml -- approx 75 will have cancer. Since PSA is not specific for Ca, PSA Velocity PSA density are used to detect Prostate cancer. PSA velocity is the rate of change in PSA levels over time and is expressed most commonly as the PSA doubling time. For men with a PSA above 4, PSA velocity of more than .75 ngml year is suggestive of Ca. While for those with lower PSA levels, rates above 0.5 ngmL per year should be used to advise biopsy. PSA density is calculated by dividing the serum PSA by the estimated prostate weight measured by TRUS. It was developed to correct for the contribution of BPH to the total PSA level. - Values 0.10 are consistent with BPH. - 0.15 suggest cancer 