prostate cancer, does not differentiate from BPH (Benign Prostatic Hyperplasia). In this circumstance it is advisable to perform free PSA

 

Ultra Sensitive Assay Technology

Use of third generation Streptavidin–Biotin based

immunoassays will enhance the sensitivity and specificity

of the assay.

Short Notes on Different Tumor Markers

PSA (Prostate Specific Antigen)

¾ It is a 33 KDa single chain glycopeptide produced only

in the prostatic secretory epithelium

¾ It is a major protein in the seminal plasma

¾ Because it is a serine protease, it forms complex in the

serum with various protease inhibitors

¾ The major PSA complex detected in the serum is the

PSA –α1 –antichymotrypsin (PSA –ACT) complex. It is

also bound with α 2-chymotrypsin (PSA – A2M)

¾ The tissue specificity makes it the most useful marker

for the diagnosis and treatment of prostate cancer

¾ A small portion of psa remains free in the blood unbound

to any carrier protein. This portion is “Free PSA”.

Issues of PSA Diagnosis

Determination of PSA value in the serum is a good indicator

for prostate cancer. But like any laboratory test, there is a

significant overlap between PSA levels found in cancer and

benign prostatic hyperplasia. Thus, it is important to obtain

sequential levels in low or borderline elevated values. A

rise in the level as compared to an earlier measurement is

an ominous sign.

What are the Limitations of PSA Testing?

Detection does not always mean saving lives

¾ False positive tests

¾ False negative tests

¾ Elevation in different conditions.

Role of Free PSA

The introduction of free PSA (f-PSA) testing has

introduced a greater level of specificity in identifying

early prostate cancer. In 1998, the FDA between 4.0-10.0.

This has often been the diagnostic gray zone for total

approved f-PSA testing as a diagnostic aid for men with

Malignant disease Multiple markers Comment

Metastatic breast cancer CA 15-3 and MCA Differentiate from adenocarcinoma of other primary site

Pancreatic cancer CEA and CA 19-9 Elevation of both specific for pancreatic cancer

Ovarian and colorectal

adenocarcinoma

CA 125 to CEA ratio Discrimination between ovarian and colorectal adenocarcinomas

Testicular cancer HCG and AFP Together used are most useful in staging and monitoring of testicular cancer

Criteria for Ideal Immunoassay

Application Specificity Sensitivity Precision Conc. Range

Screening Less critical Critical Less critical Not critical

Diagnosis Highly desirable Highly desirable Less critical Not critical

Monitoring Less critical Desirable Critical Wide range desirable

Recurrence Important Highly desirable Less critical Not critical

Prognosis Not critical Critical Not critical Not critical

682 Concise Book of Medical Laboratory Technology: Methods and Interpretations total PSA values PSA testing and f-PSA may aid in the

stratification.

New Concepts in Prostate Cancer Diagnosis

The value of total PSA, even though an indicator for

prostate cancer, does not differentiate from BPH (Benign

Prostatic Hyperplasia).

In this circumstance it is advisable to perform free PSA

and PSA ratio.

What is PSA Ratio?

It is the ratio of free and bound PSA in the body. It is also

known as FREE PSA%.

 Free PSA in sample Free PSA % = ___________________________ × 100 Total PSA in sample

Advantages of PSA Ratio Testing

¾ It enhances the specificity of PSA testing in prostate

cancer.