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PSA (Total)
Prostate Specific antigen (PSA) is a serine protease with chymotrypsin-like activity. The protein is a single chain glycoprotein with a molecular weight of 28.4 kDA. PSA derives its name from the observation that it is a normal antigen of the prostrate but is not found in any other normal or malignant tissue.
PSA is found in benign, malignant and metastatic prostrate cancer. Since prostate cancer is the second most prevalent form of male malignancy, the detection of elevated PSA levels plays an important role in the early diagnosis. Serum PSA levels have been found more useful than prostatic acid phosphatase (PAP) in the diagnosis and management of patients due to increased sensitivity.
May be diagnosed by:
- Determination of specific antibodies based on the ELISA technique
- Determination of specific antibodies based on the RIA-technique
PSA (Total) ELISA:
Total PSA kit is a direct solid phase enzyme immunoassay for quantitative determination of Total Prostatic Specific Antigen (tPSA) in human serum or plasma.
Principle of the Assay:
In this method, standards, patient specimens and/or controls (containing the native tPSA antigen) are first added to streptavidin coated wells. Biotinylated monoclonal and enzyme labelled antibodies are then added and the reactants are mixed: these antibodies have high affinity and specificity and are directed against distinct and different epitopes of tPSA.
Reaction between the various tPSA antibodies and native tPSA occurs in the microwells without competition or steric hindrance, forming a soluble sandwich complex.
The interaction is illustrated by the following equation:
Ka |
BtnAb(m) = Biotinylated Monoclonal Antibody (Excess Quantity)
AgtPSA = Native Antigen (Variable Quantity)
EnzAb = Enzyme labelled Antibody (Excess Quantity)
EnzAb-AgtPSA-BtnAb(m) = Antigen-Antibodies Sandwich Complex
ka = Rate Constant of Association
k-a = Rate Constant of Dissociation
Simultaneously, the complex is fixed to the well through the high affinity reaction of streptavidin and biotinylated antibody. This interaction is illustrated below:
EnzAb -AgtPSA-BtnAb(m) + StreptavidinC.W -> Immobilized Complex |
Streptavidin CW = Streptavidin immobolized on well.
Immobilized Complex = Antibodies-Antigen sandwich bound.
After equilibrium is attained, the antibody-bound fraction is separated from unbound antigen by decantation or aspiration. The enzyme activity in the antibody-bound fraction is directly proportional to the native antigen concentration. The activity of the enzyme present on the surface of the well is quantitated by reaction with a suitable substrate to produce colour. By utilizing several different calibrators of known antigen values, a dose response curve can be generated from which the antigen concentration of an unknown can be ascertained.
Specific performance characteristics:
Intraassay | Analytical Sensitvity | ||||
PSA (Total) | n | mean | SD | C.V. |
|
Level 1 | 20 | 0.7 | 0.05 | 7.1% | 0.012 |
Level 2 | 20 | 4.5 | 0.20 | 4.4% | |
Level 3 | 20 | 28.3 | 1.07 | 3.7% | |
Interaassay | Analytical Sensitivity | ||||
PSA (Total) | n | Mean | SD | C.V | |
Level 1 | 10 | 0.8 | 0.09 | 11.3 | 0.012 |
Level 2 | 10 | 4.3 | 0.25 | 5.8 | |
Level 3 | 10 | 27.5 | 1.42 | 5.2 | |
Correlation with RIA performed on 241 samples is r = 0.987
Order information:
ELISA | Number of Determinations | Product Number |
PSA (Total) | 96 | DNOV064 |
