PSA, Total Serum

Immunology

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Description

The main application of all tumour markers is monitoring for relapse or progression. Use as a diagnostic aid requires care and knowledge of the test limitations. Opportunistic screening is discouraged. The major source of prostate specific antigen (PSA) is the ductal and acinar epithelium of the prostate, from where it is secreted into the seminal plasma. PSA is a zymogen of a 33 kDa serine protease with extensive homology with the glandular kallikreins. The predominant molecular form present in serum is the 80-90 kDa complex of PSA with a1-antichymotrypsin (ACT), free PSA represents a relatively minor but variable fraction of the total serum PSA concentration [2]. PSA is the tumour marker of choice for prostate cancer. It demonstrates high tissue specificity and serum levels correlate well with tumour mass and clinical stage. 50% of patients with the tumour restricted within the prostate capsule show elevation over 10ug/L whereas this increases to 90% in patients with metastatic spread. Elevated concentrations cannot be considered diagnostic of prostatic cancer in view of the elevations seen in up to 15% of patients with benign prostatic hypertrophy [2,4]. NICE guidance for the diagnosis and treatment of prostate cancer recommend a combination of PSA measurement and rectal examination, with ultrasonography when investigating the condition. They also state that a raised PSA alone should not automatically lead to a prostate biopsy [1]. Use of percent free PSA further improves the specificity of PSA testing, particularly in the range of 4-10 ug/L, at which most false positive PSA tests occur [3]. Persistent elevation of PSA following treatment or an increase in the pre-treatment PSA concentrations is indicative of recurrent or residual disease. NICE guidelines recomment that PSA is checked every year in patients not on treatement, and every 6 months for 2 years in patients undergoing therapy, followed by yearly monitoring [1].

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Indications

Diagnosis and monitoring of prostate cancer.

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Sample Type

2mL Serum (Gel 5mL Yellow tube). Requests from outside Sheffield: Transport at ambient temperature via Royal Mail or Courier.

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Reference Range

1. Results <3ng/mL (for all ages):In patients on Finesteride/ Dutasteride (5a-reductase inhibitors) the measured PSA result should be doubled before interpreting.See Public Health England Guidance: PCRMP: benefits and risks of PSA testing.2. Results between 3.01 and 20.0 ng/mL (for all ages):NOTE: PSA result over 3ng/mL. Should be repeated at least 4 weeks later (6 weeks if treated for UTI) to confirm.If the repeat PSA level remains above 3ng/mL then consider a 2 week wait referral to Urology as per local guideline.In patients on Finesteride/ Dutasteride (5a-reductase inhibitors) the measured PSA result should be doubled before interpreting.Note: Some benign conditions may elevate PSA (BMJ 2009;339:b3527)See Public Health England Guidance: PCRMP: benefits and risks of PSA testing.3. For PSA results greater than 20.0ng/mL (for all ages):NOTE: PSA result over 20ng/mL. Consider a 2 week wait referral to Urology without repeating the test as per local guideline.Note: Some benign conditions may elevate PSA (BMJ 2009;339:b3527)See Public Health England Guidance: PCRMP: benefits and risks of PSA testing.

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Turnaround Time

Within 2 days

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Testing Frequency

Daily

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External Notes

Tumour Markers are not diagnostic and are of most use in monitoring response to treatment and early detection of relapse. Normal values do NOT exclude malignancy. Quoted ranges only valid for serum.

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References

NICE Clinical Guideline 58 - Prostate cancer diagnosis and treatment. 2008 [Ref 1]PRU Handbook of Clinical Immunochemistry. 9th Edition. 2007. [Ref 2]Canto EI, and Slawin KM. Early management of prostate cancer: how to respond to an elevated PSA? Annu Rev Med. 2002. 53:355-368. [Ref 3]Milford Ward A, Catto JWF, Hamdy FC. Prostate Specific Antigen: biology, biochemistry and available commercial assays. Annals of Clinical Biochemistry. 2001. 38:633-651. [Ref 4]Duffy M.J. Tumour Markers in Clinical Practice: A review focusing on common solid cancers. Med Princ Pract. 2013. 22: 4-11.

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See Also

PSA Index

Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.