Free PSA

Key Features and Values
  • Same sample type can be used across all assays to simplify inclusion into routine serology work-up
  • Ready to use reagents reduces hands-on time for assay preparation
  • Long shelf life cost-effective solution by reducing wastage due to expired kit
  • Suitable for inclusion on automated plate systems simplifies scale-up of test volume
  • Supported by a complete panel of assays for supporting treatment monitoring of several forms of cancer
Product Description

Free PSA ELISA is used for the quantitative determination of free Prostate Specific Antigen (f-PSA) in human serum or plasma samples. The determination of f-PSA levels is generally used in conjunction with a total PSA (t-PSA) measurement to determine the ratio between f-PSA and t-PSA. This ratio helps to estimate the risk for prostate cancer and to discriminate between elevated t-PSA levels caused by cancerous or non-cancerous conditions. F-PSA determinations are especially recommended for men with elevated t-PSA levels and negative results with digital rectal examination (DRE) in order to decide if a second prostate biopsy is indicated.

Scientific Description
Prostate cancer is the most frequent type of cancer found in man and is the second cause of death due to cancer in males.  Until recently, digital rectal examination (DRE) was frequently used as only diagnostic modality for the detection of early stages of prostate cancer.  In the recent years the determination of serum PSA levels has become the most accepted method to improve the diagnostic specificity of DRE.  Although PSA is a tissue specific protein and is not solely tumour specific, it has become the most important marker for prostate carcinoma, showing a better specificity than other biochemical markers used in this context (PAP, total alkaline phosphatase, carcinoembryonic antigen, etc.).
In 1979, Wang et al. isolated a specific antigen for normal prostate tissue and called this protein PSA.  PSA is a 33 kDa serine proteinase.  Immunohistological studies have shown that PSA is localised in the cytoplasm of prostate acinar cells, ductal epithelium and in the secretion on the ductal lumina, present in normal, benign hyperplastic and malignant prostate tissues as well metastatic prostate cancer and in seminal plasma.  If the structural integrity of the prostate is disturbed and/or the gland size is increased, the amount of PSA in the blood plasma may become elevated.  In the blood plasma, most of the PSA forms complexes with various proteinase inhibitors.  Only a small fraction of PSA circulates as free inactive PSA.  Basically three major forms of PSA can be distinguished, only two of which are immunoreactive.  The predominant form of PSA is a complex with α1-antichymotrypsin (ACT-PSA).  Inactive free PSA (f-PSA) represents around 10-40% of the immunologically detectable PSA.  The total amount of immunoreactive PSA is known as total PSA (t-PSA).  PSA complexed with α- 2-macroglobulin cannot be detected by immunological assays and is therefore frequently called occult PSA (o-PSA).
Current methods of screening men for prostate cancer utilise the detection of t-PSA.  Levels of 4.0 ng/ml or higher are strong indicators of the possibility of prostatic cancer and are an indication for follow-up examinations of the patient.  However, elevated serum PSA levels are frequently also attributed to benign prostatic hyperplasia, leading to a high percentage of false positive screening results.  A potential solution to this problem involves the determination of free PSA levels.  Studies have suggested that the percentage of free PSA is lower in patients with prostate cancer than those with benign prostatic hyperplasia.  Thus, the measurement of free serum PSA in conjunction with total PSA, can improve specificity of prostate cancer screening in selected men with elevated total serum PSA levels, which would subsequently reduce unnecessary prostate biopsies with minimal effects on cancer detection rates.
Publications

1. World Cancer Report. World Health Organisation. 2014. Chapter 5.11 ISBN 978-9283204299
2. Henttu P and Vihko P. Prostate-specific antigen and human glandular kallikrein: two kallikreins of the human prostate. Amm Med 1994, 26(3):157-64.
3. Balk SP, Ko YL and Bubley GJ. Biology of prostate specific antigen. J Clin Oncol. 2003, 15;21(2):383-91.
4. Zhou AM et al. Multiple forms of prostate-specific antigen in serum: differences in immunorecognition by monoclonal and polyclonal assays. Clin Chem. 1993, 39(12):2483-91.
5. Fritsche HA and Babalan RJ. Analytical performance goals for measuring prostate-specific antigen. Clin Chem, 1993, 39: 1529-1529.
6. Velonas VM, Woo HH, dos Remedios CG, Assinder SJ. Current status of biomarkers for prostate cancer. Int J Mol Sci. 2013, 24;14(6):11034-60.
7. Gion M et al. Percent free prostate-specific antigen in assessing the probability of prostate cancer under optimal analytical conditions. 1998, Clin Chem 44(12):2462-70.
8. Akdas et al. The role of free prostate specific antigen in the diagnosis of prostate cancer. British J Urol,1997, 79: 920-923.
9. Chen YT et al. Using proportions of free to total prostate-specific antigen, age and total prostate specific antigen to predict the probability of prostate cancer. Urology, 1996, 47(4):518-24.
10. Catalona et al. Use of the percentage of free prostate specific antigen to enhance differentiation of prostate cancer from benign prostatic disease: a prospective multicenter clinical trial. JAMA, 1998, 20;279(19):1542-7.
11. Liu J et al. Establishment of two new predictive models for prostate cancer to determine whether to require prostate biopsy when the PSA level is in the diagnostic gray zone (4-10 ng ml-1). Asian J Androl. 2019 21:1-4.
12. Huang Y, Li ZZ, Huang YL, Song HJ, Wang YJ. Value of free/total prostate-specific antigen (f/t PSA) ratios for prostate cancer detection in patients with total serum prostate-specific antigen between 4 and 10 ng/mL: A meta-analysis. Medicine (Baltimore). 2018; 97(13).
13. Duffy MJ. Biomarkers for prostate cancer: prostate specific antigen and beyond. Clin Chem Lab Med. 2019, 12. aop.
14. Carlsson SV and Roobol MJ. Improving the evaluation and diagnosis of clinically significant prostate cancer in 2017. Curr Op in Urol. 2017 27(3): 198–204.
15. Milford Ward A et al. Prostate specific antigen: biology, biochemistry and available commercial assays. Ann Clin Biochem, 2001, 38: 633-651.
16. Price CP et al., Pre-and post-analytical factors that may influence use of serum prostate specific antigen and its isoforms in a screening program for prostate cancer. Ann Clin Biochem, 2001, 38: 188-216.
17. Ferguson J et al. Continued provision of WHO International Standards for total and free PSA: Content and commutability of replacement preparations. Clin Biochem. 2019 71:58-66.

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Code: DKO138
Clinical Area:
Incubation: 60+60+15 min
Sensitivity: N/A
Specificity: N/A
Classification: IVD, CE
Number of Tests: 96
Sample Type: Serum or plasma (heparin, citrate or EDTA)
Sample Volume: 25 μL
Assay Range: 0.95 - 12 ng/mL