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Year : 2006  |  Volume : 22  |  Issue : 3  |  Page : 279-280

Free PSA estimation substituted by calculation where total PSA value is up to 4 ng/ml

Thyrocare Technologies Ltd., Mumbai, India

Correspondence Address:
C Sengupta
Thyrocare Technologies Ltd., Corporate Center B, Opp. Hotel Lotus Suites, Marol Pipe Lines, Andheri Kurla Road, Andheri (East), Mumbai - 400 059
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-1591.27645

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How to cite this article:
Dhumne M, Sengupta C, Kadival G, Nirmala R, Rathinaswamy A, Velumani A. Free PSA estimation substituted by calculation where total PSA value is up to 4 ng/ml. Indian J Urol 2006;22:279-80

How to cite this URL:
Dhumne M, Sengupta C, Kadival G, Nirmala R, Rathinaswamy A, Velumani A. Free PSA estimation substituted by calculation where total PSA value is up to 4 ng/ml. Indian J Urol [serial online] 2006 [cited 2022 Jul 2];22:279-80. Available from:

Dear Sir,

Prostate specific antigen (PSA) is protein, produced in high levels by the prostate gland in men and very little amount is leaked into the blood, due to the presence of basement membrane, under normal conditions.[1] Enzymatically active PSA leaked into serum is inactivated by irreversible binding to antichymotrypsin (ACT) and macroglobulin; major protease inhibitor in serum; and form complex PSA (cPSA). Macroglobulin-bound PSA is not accessible for immunodetection due to steric shielding. The PSA-ACT complex is a major molecular form of PSA in serum.[2] A small percent of PSA still exists in the free form (fPSA), approximately 1 million ng/ml of fPSA concentration can be found in the ejaculate. In men with prostate cancer, levels of fPSA are significantly lower and of cPSA are higher than those in men with benign hyperplasia or normal conditions[3] which may be due to structural changes in the PSA molecule produced by cancerous cells.

Using immunoassays, investigators demonstrated that the ratio of free-to-total PSA was lower in men with prostate cancer. In cases where PSA values are 4-10 the ratio is more discriminatory.[4] Therefore PSA estimation alone does not depict a clear picture of the prostate malignancy[5] and cPSA, fPSA estimation is necessary as well. There are various technologies available for the estimation of each one of them and although correlation coefficients between various assays are high, biases do occur. This variability is of importance in clinical situations, such as screening. Our aim was to find out the correlation of calculated free PSA with estimated free PSA.

At Thyrocare Technologies Ltd., serum samples collected from all over the country through authorized collection centers were tested for PSA and cPSA using ADVIA- CENTAUR, BAYER, USA and fPSA was tested using IMMULITE, DPC, USA. All analyzers work on the principle of Chemiluminescence Immunoassay techniques. Seventy-four samples received during the period of 1st June 2005 to 31st December 2005 and analyzed for PSA, cPSA and fPSA were selected for the study.

We obtained fPSA value (calculated fPSA) by subtracting cPSA values from corresponding PSA values. Calculated fPSA values were then compared with estimated fPSA [Figure - 1]. For samples where PSA value is less than 4 ng/ml there is good correlation between estimated and calculated free PSA; as the total PSA value increases the correlation decreases. A regression coefficient of 0.8672 indicates good correlation between estimated and calculated values [Figure - 2].

We conclude that free PSA can be reported using simple calculation from PSA and cPSA in cases where PSA is up to 4 ng/ml. But wherever PSA values are exceeding the normal range of 4 ng/ml, fPSA is suggested to be estimated. The probable reason is that at the higher side of the linearity, the apparent slight variation becomes amplified which is negligible when values are less.

   References Top

1.Brawer M, editor. Prostate specific antigen. Marcel Dekker Publications: 2001.  Back to cited text no. 1    
2.Gleave M, Goldenberg L. Prostate specific antigen as a prognostic predictor for prostate cancer. British Columbia Cancer Agency, Vancouver, British Columbia, Canada.  Back to cited text no. 2    
3.Stenman UH, Leinonen J, Alfthan H, Rannikko S, Tuhkanen K, Alfthan O. A complex between prostate specific antigen and al-antichymotrypsin is the major for of prostate specific antigen in serum of patients with prostatic cancer: Assay the complex improves clinical sensitivity for cancer. Cancer Res 1991;5:222-6.  Back to cited text no. 3    
4.Catalona WJ. Clinical utility of measurements of free and total prostate specific antigen: A review. Prostate Suppl 1996;7:64-9.  Back to cited text no. 4  [PUBMED]  
5.Lein M, Koenig F, Jung K, McGovern FJ, Skates SJ, Schnorr D, Loening SA. Ratio of free prostate specific antigen to total prostate specific antigen in a population of 1160 healthy men. Br J Urol 1998;82:231-6.  Back to cited text no. 5  [PUBMED]  


  [Figure - 1], [Figure - 2]


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