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Test Code FPSA or LAB171 Free Prostate-Specific Antigen, Serum or Plasma

Important Note

For Free PSA requests, a Total PSA is performed first. Total PSA values between 4 and 10 ng/mL will reflex a Free PSA.

Specimen Requirements

Container Type:

Optimal: Gold or Mint*

*For STAT requests

Acceptable: Red or Green
Optimal Collection Volume: 

4.5mL; full tube
Minimum Volume:

1 mL whole blood
Collection Instructions:

Gently invert the sample 5-6 times after collection.
Specimen Transport:

Refrigerate
Processing Instructions: 

1. If serum, allow the specimen to clot for 30 minutes.

2. Centrifuge specimen within 2 hours of collection.

3. After centrifugation, specimen tubes without a gel barrier should have the serum or plasma aliquoted to a false bottom container.

4. Keep serum or plasma refrigerated until testing can be performed.

Specimen Stability

Specimen Type Temperature Time
Serum* Refrigerated 5 days
Room Temperature 8 hours
Frozen 3 months

*Note: Heparinized plasma in gel separator tubes is less stable than serum and is only suitable for add-on testing up to 2 days following sample collection.

Specimen Rejection Criteria

Hemolysis Mild OK; Moderate OK; Gross Reject
Lipemia Mild OK; Moderate OK; Gross Reject
Icterus Mild OK; Moderate OK; Gross Reject
Other Quantity not sufficient

Useful For

Free PSA testing is used as an aid in distinguishing prostate cancer from benign prostatic conditions when used in conjunction with Total PSA for prostate detection in men aged 50 or older who have Total PSA values between 4 and 10 ng/mL and digital rectal examinations that are not suspicious for cancer. A prostatic biopsy is required for the diagnosis of cancer.

Methodology

Roche Cobas - Electrochemiluminescence assay

 

Note: Values from different methods may give different results and cannot be used interchangeably.

Reference Ranges

Probability of prostate cancer, based on % free PSA and patient age:

 

Males

% fPSA ratio

Probability of Prostate Cancer

50-59 yrs

60-69 yrs

> 70 yrs

< 10

49.2

57.5

64.5

11-18

26.9

33.9

40.8

19-25

18.3

23.9

29.7

> 25

9.1

12.2

15.8

Note: For males aged less than 50 years, the probability of prostate cancer has not been established. 

 

Females

Not applicable

Interpretive

PSAFT - Clinical & Interpretive: Prostate-Specific Antigen (PSA), Total and Free, Serum (mayocliniclabs.com)

Day(s) Performed

24/7

Expected TAT

Same day

Performing Laboratory

Bronson Laboratory, Chemistry - Kalamazoo

Sample Retention Time

7 days

CPT Code

  • Total PSA: 84153
  • Free PSA: 84154

LOINC Code

  • Total PSA: 83112-3
  • Free PSA: 83113-1