Prostate Specific Antigen (PSA), Free (Unbound)
| Label Mnemonic: | FPSA |
| Epic code: | LAB117 |
| Downtime form: | A-1a Doctor/Provider Orders - Pathology Core and Specialty Care Nursery |
Chemistry
6240 RCP
356-3527
6240 RCP
356-3527
Specimen(s):
Plasma
Collection Medium:
 |
| Plasma Separator Tube 4.5 mL |
Alternate
Collection Media:
Call laboratory for additional acceptable specimen collection containers.
Minimum:
3 mL whole blood in light green top tube or TWO
Microtainer® devices.
Testing Schedule:
24 hrs/day, 7 days a week, including holidays.
Turn Around
Time:
1 hour (upon receipt in laboratory)
Reference Range:
No accepted reference range. There is an increased probability of
prostate cancer with lower %FPSA.
Comments:
Assay updated with increased tolerance to biotin on 11/9/21.
Prostate-specific antigen (PSA) is a glycoprotein (molecular weight 30,000-34,000 daltons) having a close structural relationship to glandular kallikrein. It has the function of a serine protease.
The proteolytic activity of PSA in blood is inhibited by the irreversible formation of complexes with proteinase inhibitors such as alpha-1-antichymotrypsin, alpha-2-macroglobulin and other acute phase proteins. In addition to being present in these complexes, PSA is also present in blood in the free form, but is proteolytically inactive.
PSA tests lack sufficient sensitivity and specificity to be considered ideal or absolutely diagnostic for screening or early detection because PSA is not specific for prostate cancer. PSA is organ specific, being produced primarily by prostatic secretory epithelium, but has long been known to be elevated in non-malignant conditions such as benign prostatic hyperplasia (BPH). A number of studies have found that the % free PSA was significantly lower in patients having prostate cancer than those with benign disease or normal controls. The ratio fPSA/tPSA has been demonstrated to improve the sensitivity and specificity in patients with tPSA values in the "gray zone" of 4-10 ng/mL.
An equimolar tPSA determination is the prerequisite for reliable ratios.
In patients receiving therapy, particularly hormone withdrawal therapy, the fPSA/tPSA ratio cannot be utilized to differentiate prostate hyperplasia from cancer of the prostate. Combining tests from different manufacturers to determine tPSA and fPSA can produce erroneous values, since total PSA tests may be standardized by differing methods or detect free PSA to differing degrees.
The free PSA immunoassay is indicated for measurement of fPSA in conjunction with the total PSA assay to develop a ratio of fPSA to tPSA (%fPSA). This ratio is useful when used in conjunction with the Total PSA test as an aid in distinguishing prostate cancer from benign prostatic conditions in men age 50 years or older who have a digital rectal examination (DRE) that is not suspicious for prostate cancer and an total PSA value in the range 4-10 ng/mL. Prostate biopsy is required for the diagnosis of prostate cancer.
This test is also performed in the Iowa River Landing (IRL) clinical laboratory (for specimens drawn at that site).
Prostate-specific antigen (PSA) is a glycoprotein (molecular weight 30,000-34,000 daltons) having a close structural relationship to glandular kallikrein. It has the function of a serine protease.
The proteolytic activity of PSA in blood is inhibited by the irreversible formation of complexes with proteinase inhibitors such as alpha-1-antichymotrypsin, alpha-2-macroglobulin and other acute phase proteins. In addition to being present in these complexes, PSA is also present in blood in the free form, but is proteolytically inactive.
PSA tests lack sufficient sensitivity and specificity to be considered ideal or absolutely diagnostic for screening or early detection because PSA is not specific for prostate cancer. PSA is organ specific, being produced primarily by prostatic secretory epithelium, but has long been known to be elevated in non-malignant conditions such as benign prostatic hyperplasia (BPH). A number of studies have found that the % free PSA was significantly lower in patients having prostate cancer than those with benign disease or normal controls. The ratio fPSA/tPSA has been demonstrated to improve the sensitivity and specificity in patients with tPSA values in the "gray zone" of 4-10 ng/mL.
An equimolar tPSA determination is the prerequisite for reliable ratios.
In patients receiving therapy, particularly hormone withdrawal therapy, the fPSA/tPSA ratio cannot be utilized to differentiate prostate hyperplasia from cancer of the prostate. Combining tests from different manufacturers to determine tPSA and fPSA can produce erroneous values, since total PSA tests may be standardized by differing methods or detect free PSA to differing degrees.
The free PSA immunoassay is indicated for measurement of fPSA in conjunction with the total PSA assay to develop a ratio of fPSA to tPSA (%fPSA). This ratio is useful when used in conjunction with the Total PSA test as an aid in distinguishing prostate cancer from benign prostatic conditions in men age 50 years or older who have a digital rectal examination (DRE) that is not suspicious for prostate cancer and an total PSA value in the range 4-10 ng/mL. Prostate biopsy is required for the diagnosis of prostate cancer.
This test is also performed in the Iowa River Landing (IRL) clinical laboratory (for specimens drawn at that site).
Test
Limitations:
The assay is unaffected by icterus (bilirubin < 65 mg/dL), hemolysis (Hb is less than 2200 mg/dL), lipemia (Intralipid is less than 1500 mg/dL) and biotin is less than 1200 ng/mL (criterion: recovery within plus or minus 10% of initial value). In vitro tests were performed on 28 commonly used pharmaceuticals. As with all tests containing monoclonal mouse antibodies, erroneous findings may be obtained from samples taken from patients who have been treated with monoclonal mouse antibodies or have received them for diagnostic purposes. Free PSA contains additives which minimize these effects. In rare cases, interference due to extremely high titers of antibodies to streptavidin can occur. There is no high-dose hook effect for free PSA concentrations up to 15,000 ng/mL. No influence was observed from rheumatoid factor (up to 1500 U/mL). For diagnostic purposes, the free PSA findings should always be assessed in conjunction with the patient's medical history, clinical examination and other findings.
Methodology:
Electrochemiluminescence Immunoassay
CPT Code:
84154