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.

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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