Prostate-specific antigen test

Carter, H. B., Epstein, J. I., Chen, D. W., et al. Recommended prostate-specific antigen testing intervals for the detection of curable prostate cancer. JAMA 227,1456-1460 (1997). 

Prostate-specific antigen (PSA) Blood test for this chemical secreted by the prostate Less than 4 ng/mL (4 mcg/L) Greater than or equal to 4 ng/mL (4 mcg/L)... 

Prostate-specific antigen (PSA) a substance secreted by the prostate and normally carried by ducts to the urethra during ejaculation PSA is used as a screening test for prostate cancer. 

The performance of the BioCD under assay conditions has been tested using several gold standard systems. These are assays of anti-rabbit and anti-mouse IgG systems, prostate specific antigen (PSA), and haptoglobin. Incubations have been performed under equilibrium conditions without transport limitation, and also under transient conditions as ambient assays that are diffusion limited. Ambient assays are performed in practice, while equilibrium assays provide more information about the performance of the antibodies and provides a quantitative estimate for equilibrium dissociation constants. 

Forensic biochemists perform blood typing and enzyme tests on body fluids in cases involving assault, and also in paternity cases. Even tiny samples of blood, saliva, or semen may be separated by electrophoresis and subjected to enzymatic analysis. In the case of rape, traces of semen found on clothing or on the person become important evidence the composition of semen varies from person to person. Some individuals excrete enzymes such as acid phosphatase and other proteins that are seldom found outside seminal fluid, and these chemical substances are characteristic of their semen samples. The presence of semen may be shown by the microscopic analysis for the presence of spermatozoa or by a positive test for prostate specific antigen. 

Other enzymes are also useful indices of liver pathology. Serum alkaline phosphatase is often a useful indicator of liver and bone disease. The alkaline phosphatases are a diverse group of enzymes that catalyze reactions in which a phosphate is removed from a phosphate ester, especially at an alkaline pH. Physicians don t care about this. They do care that serum alkaline phosphatase levels often rise with bone breakdown (as in tumor infiltration) and in liver disease, especially where tliere is obstruction of the bile duct. Acid phosphatase is particularly rich in the prostate. A rise in its serum levels provides a test as to the presence of prostate carcinoma. This test has largely been replaced by assay for Prostate Specific Antigen (PSA), a serine protease that is elevated in prostatic carcinoma. 

Figufe 15-1 Prostate-specific antigen (PSA) levels for patients with benign prostatic hyperplasia (BPH) and known prostatic carcinoma (CA) are shown with two decision-level cutoffs. Tests A and B in Table 15-4 were actually the same test with two different cutoffs. 

Figure 15-2 Receiver operating characteristic curve of prostate-specific antigen (PSA). Each point on the curves represents a different decision level.The sensitivity (true-positive rate) and I— the specificity (false-positive rate) can be read for Tests A and B. The true-positive and false-positive rates are demonstrated using 4 and IO Xg/L as decision thresholds.

Figure S-3 Receiver operating characteristic curves of prostatic acid phosphatase (PAP) and prostate-specific antigen (PSA) assays for patients with benign prostatic hyperplasia and prostatic carcinoma. Because the PSA assay curve is above the PAP assay curve at ail points, the PSA assay is the better assay for the patients tested.

Coplen DE, Yuan JJ, Petros JA, Andriole GL. Measurement of prostate-specific antigen in serum as a screening test for prostate cancer. N Engl J Med. 1991 324 1156-61. Erratum in N Engl J Med 1991 325 1324. 

Changes in analytical bias directly shift the distribution of the patient test values. If the elevated values on a test are associated with specific clinical actions, then the shifts in analytical bias can notably alter the number of patients having test values that exceed the action limit. For example, for a serum calcium assay with an action limit of lO.i mg/dL, an upward bias of 0.2 mg/dL changes the number of patients subjected to further investigation from 6.5% to 15.0%. Similarly, analytical shifts in other critical analytes can cause notable clinical problems, such as false elevations of prostate-specific antigen values triggering prostate ultrasound examinations and biopsies and false elevation of TSH triggering additional thyroid examinations. These small analytical shifts can have major downstream effects on healthcare costs. 

Jung, K., Zachow, J., Lein, M., Brux, B., Sinha, P., Lenk, S., Schnorr, D., and Loen-ing, S. A. (1999) Rapid detection of elevated prostate-specific antigen levels in blood performance of various membrane strip tests compared. Urology. 53, 155-160... 

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