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Test ID: PSAFT    
Prostate-Specific Antigen (PSA), Total and Free, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

The percentage of measured prostate-specific antigen (PSA) existing in the free form (free:total PSA ratio) is useful in assessing the risk of prostate cancer in patients with borderline or moderately increased total PSA (4.0-10.0 ng/mL) and has been used to help select men who should have follow-up prostate biopsy.

 

Most prostate cancers are slow growing, so the utility of prostate cancer screening is marginal in most men with a life expectancy of <10 years.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Prostate-specific antigen (PSA) is a glycoprotein that is produced by the prostate gland, the lining of the urethra, and the bulbourethral gland. Normally, very little PSA is secreted in the blood. Increases in glandular size and tissue damage caused by benign prostatic hypertrophy, prostatitis, or prostate cancer may increase circulating PSA levels.

 

PSA exists in serum in multiple forms: complexed to alpha-1-anti-chymotrypsin (PSA-ACT complex), unbound (free PSA), and enveloped by alpha-2-macroglobulin (not detected by immunoassays).

 

Higher total PSA levels and lower percentages of free PSA are associated with higher risks of prostate cancer.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

TOTAL PSA

Males:

Age (Years)

PSA Upper Limit (ng/mL)

<40

< or =2.0

40-49

< or =2.5

50-59

< or =3.5

60-69

< or =4.5

70-79

< or =6.5

> or =80

< or =7.2

 

Females: not applicable

 

FREE PSA

Males: When total PSA is in the range of 4.0-10.0 ng/mL, a free:total PSA ratio < or =0.10 indicates 49% to 65% risk of prostate cancer depending on age; a free:total PSA ratio >0.25 indicates a 9% to 16% risk of prostate cancer, depending on age.

Females: not applicable

Interpretation Provides information to assist in interpretation of the test results

When total prostate-specific antigen (PSA) concentration is <2.0 ng/mL, the probability of prostate cancer in asymptomatic men is low, further testing and free PSA may provide little additional information. When total PSA concentration is >10.0 ng/mL, the probability of cancer is high and prostate biopsy is generally recommended.

 

The total PSA range of 4.0 to 10.0 ng/mL has been described as a diagnostic "gray zone," in which the free:total PSA ratio helps to determine the relative risk of prostate cancer (see table below). Therefore, some urologists recommend using the free:total ratio to help select which men should undergo biopsy. However even a negative result of prostate biopsy does not rule-out prostate cancer. Up to 20% of men with negative biopsy results have subsequently been found to have cancer. 

 

Based on free:total PSA ratio: the percent probability of finding prostate cancer on a needle biopsy by age in years:

Free:total PSA ratio

50-59 years

60-69 years

> or =70 years

< or =0.10

49.2%

57.5%

64.5%

0.11-0.18

26.9%

33.9%

40.8%

0.19-0.25

18.3%

23.9%

29.7%

>0.25

9.1%

12.2%

15.8%

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Normal results do not eliminate the possibility of prostate cancer.

 

Values obtained with different assay methods or kits may be different and cannot be used interchangeably.

 

Tumor markers are not specific for malignancy. Test results cannot be interpreted as absolute evidence for the presence or absence of malignant disease.

 

Specimens drawn from patients undergoing prostate manipulation, especially needle biopsy and transurethral resection, may show erroneously high prostate-specific antigen (PSA) results. Care should be taken that specimens are drawn before these procedures are performed.

 

Prostate cancer patients receiving treatment with antiandrogens and luteinizing hormone-releasing factor agonists may exhibit markedly decreased levels of PSA. Also, men treated for benign prostatic hyperplasia with inhibitors of 5-alpha-reductase (finasteride) may demonstrate a significant reduction in PSA levels compared to values before treatment. Care should be taken in interpreting values for these individuals.

 

In patients receiving therapy with high biotin doses (ie, >5 mg/day), no sample should be taken until at least 8 hours after the last biotin administration.

 

In rare cases, interference due to extremely high titers of antibodies to ruthenium or streptavidin can occur.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Oesterling JE, Jacobsen SJ, Chute CG, et al: Serum prostate-specific antigen in a community-based population of healthy men. JAMA 1993 Aug 18;270:860-864

2. Catalona WJ, Smith DS, Wolfert RL, et al: Evaluation of percentage of free serum prostate-specific antigen to improve specificity of prostate cancer screening. JAMA 1995:274(15);214-1220

3. Jacobsen SJ, Bergstralh EJ, Guess HA, et al: Predictive properties of serum prostate-specific antigen testing in a community-based setting. Arch Intern Med 1996;156:2462-2468

4. Oesterling JE, Jacobsen SJ, Klee GG, et al: Free, complexed and total serum prostate specific antigen: the establishment of appropriate reference ranges for their concentrations and ratios. J Urol 1995;154:1090-1095

5. Dworschack RT, Thiel RP, Picolli SP: Clinical evaluation of the free/total PSA ratio generated with the Elecsys total and free PSA assays on the Elecsys 1010 and 2010 systems. Clin Chem 2001 Jun; 47 (6 Suppl S):A149. (Abstract)