Überdiagnostik durch PSA-Screening?
Borros M. The incidence of prostate-specific antigen PSA monitoring has increased in recent years. However, interpretation of Prostata-spezifisches Antigen PSA results is often ambiguous and leads to uncertainty for both the patient and the treating physician. Advantages and disadvantages of measuring PSA and possibilities for improved interpretation using the variable PSA quotient are given.
The prostate gland is a chestnut-sized organ that lies directly under the bladder and encloses the upper section of the urethra. It is approximately 20 to 25 g in a young man Prostata-spezifisches Antigen PSA 30 g in an older man. During ejaculation, the prostate adds up to 40 g of a milky secretion to the ejaculate, in which prostate-specific antigen PSAa protein formed by the prostate gland, is present in high concentrations.
Prostatic secretions are slightly acidic with a pH around 6. The acidity serves to neutralize vaginal alkalinity and prolong the lifespan of spermatozoa. PSA is present in low concentrations in the blood, but the concentration increases with prostate irritation, prostatic infection, and benign prostatic hyperplasia BPH.
PSA exists in the blood in two forms. PSA is primarily a tissue-specific marker. From an Prostata-spezifisches Antigen PSA PSA measurement, it is difficult to differentiate between a benign and Prostata-spezifisches Antigen PSA transformation of the prostate gland.
Distinguishing between the two is where Prostata-spezifisches Antigen PSA PSA is useful. Both tests free and total PSA have high accuracy and repeatability. With increasing age, enlargement of the prostate gland is common and, in most cases, is benign. However, it often leads to unpleasant symptoms, such Prostata-spezifisches Antigen PSA problems with urination. Prostate carcinoma is rare in men under age 50 and the average age at diagnosis is 75 years. The risk is greater for men who Prostata-spezifisches Antigen PSA relatives with prostate carcinomas.
A cure is more often possible if the tumor is recognized at an early stage; however, not all prostate carcinomas are aggressive. Some prostate carcinomas grow rapidly and metastasize. If not recognized at an early stage and treated appropriately, aggressive tumors often lead to death.
Others grow slowly, remain asymptomatic, and do not extend to other organs. Cancerous prostate Prostata-spezifisches Antigen PSA usually releases more PSA and more complexed PSA into the blood than normal, healthy tissue does. Thus, an increased PSA may indicate the Prostata-spezifisches Antigen PSA of prostate carcinoma. The higher the PSA concentration in blood, the more likely one is to find tumors that have extended beyond the prostate gland. Until recently, PSA was thought to be produced only in the prostate; however, using very sensitive methods, PSA has now been found in low concentrations in many other tissues.
The PSA molecule is very similar to kallikrein, which is androgen-dependent and produced in epithelial and glandular tissue. PSA is a glycoprotein produced predominantly, although not exclusively, by the prostate gland.
Prostata-spezifisches Antigen PSA in blood may increase as a result of a variety of pathologic conditions of the prostate and may be a suitable marker for prostate carcinoma. For men over age 50, annual PSA screening is often recommended, although the value of this screening is disputed. PSA is usually elevated in the presence of prostate carcinoma; however, many benign conditions also result in PSA elevation. The most important reason to measure PSA in blood is to screen for prostate carcinoma in men over age In addition to screening, PSA Prostata-spezifisches Antigen PSA measured to evaluate the success of treatment and progression of disease when a known prostate carcinoma is present.
Prostatic hyperplasia, one benign tumor, or several benign tumors of the prostate Prostata-spezifisches Antigen PSA. Adenomatous hyperplasia is a common condition, occurring in more than half of all men over the age of Inflammation of the prostate gland prostatitiswhich is less common. Manipulations to the prostate gland or ejaculation. In order to increase the Prostata-spezifisches Antigen PSA value of PSA measurements, the following 5 points have been found useful:.
In younger men, elevated PSA and decreased free PSA Prostata-spezifisches Antigen PSA raise suspicion of prostate cancer even at lower values than are suspicious in older men. PSA velocity should be determined. In order to evaluate PSA velocity, several accurate measurements with comparable test methods and same sample type ie, serum versus plasma are necessary.
Prostate carcinomas release much more PSA into the blood than benign prostate tumors. A small carcinoma can dramatically increase PSA levels, whereas the same increase can only be caused by a relatively large benign prostate tumor. PSA density is calculated Prostata-spezifisches Antigen PSA dividing the PSA concentration by the volume of the prostate gland as measured by ultrasound. One disadvantage of PSA density is that when a small carcinoma develops in a large benign tumor, the PSA density will be relatively low despite the presence of a carcinoma.
PSA density is thus more useful when the Prostata-spezifisches Antigen PSA gland is small than when it is large. Most PSA in the blood is bound to other proteins. With prostate carcinoma, however, the Prostata-spezifisches Antigen PSA of free PSA decreases. Why this occurs is unclear. As a result, Prostata-spezifisches Antigen PSA portion of free PSA decreases.
The reference range for the PSA quotient is greater than 0. A lower quotient strongly suggests prostate carcinoma. A higher quotient suggests BPH. As mentioned in the previous section, a majority of PSA in the blood is present in the bound form.
Bound PSA, detectable in the blood, is often complexed with alphachymotrypsin. These tests may replace traditional testing for free and total PSA. Some studies have shown improved discrimination between prostatic hyperplasia and prostate carcinoma through measuring cPSA.
PSA, prostate-specific antigen. For men with a PSA over 4. For small tumors, the risk remains that the tumor was not contained within the biopsy specimen, and an unrecognized cancer remains. In addition, prostate biopsy is an invasive procedure, which introduces the risk of contamination of the biopsy site by tumor cells.
Anti-PSA monoclonal antibodies are Prostata-spezifisches Antigen PSA to serum or plasma and incubated using standard methods and standard conditions. The following values are to be understood only as reference points as different studies have yielded different results Table 2.
The probability that a carcinoma is present rises as the proportion of free PSA decreases. The following values are reference points; different studies yield different results Table 3.
In principle, serum or plasma is suitable. Plasma should be separated by centrifugation within a short Prostata-spezifisches Antigen PSA of collection, preferably within 3 hours. The blood draw should take place prior to digital examination of the prostate gland.
When determining free Prostata-spezifisches Antigen PSA, plasma should be separated from cells Prostata-spezifisches Antigen PSA 3 hours of the blood being drawn.
Interpretation of Prostate-Specific Antigen Values Interpretation of Prostate-Specific Antigen Quotients Palpation Prostata-spezifisches Antigen PSA the prostate gland, especially prostate massage, or surgical manipulation of the prostate gland before drawing blood can lead to increased PSA values.
Elevated values decrease with a biological half-life of 2 to 3 days. Certain medications, including antiandrogens, inhibit progression of BPH and can lead to a decrease in PSA concentration. Further errors can result from the analytic measuring procedure. The total PSA measurement error depends on the characteristics of the assay employed.
The magnitude of this error is likely to be independent of the assay used. This observation holds true both for the theoretical derivation of the measurement error for the PSA quotient using the Gaussian error calculation and for the practical evaluation of the deviations from standardized control serum. The current study demonstrates that the PSA quotient should be given more attention in clinical practice. Compared with the measurement of total PSA alone, the PSA quotient is clearly associated with a much smaller measurement error 2.
Further studies are warranted on the practical relevance of the PSA quotient. Annual screening is recommended for men over 50, though some contend that PSA should not be measured Prostata-spezifisches Antigen PSA all men above Some argue that untargeted screening does Prostata-spezifisches Antigen PSA harm than good, although no one denies that more prostate carcinomas are recognized with screening. Finding an elevated PSA value may result in needless anxiety for the patient and sometimes even for the doctor and may result in unnecessary surgery with resultant impotence and urinary incompetence.
The percentage of patients with asymptomatic prostate carcinoma who would develop clinically significant disease is unknown. Prostate-specific antigen is a glycoprotein that is produced primarily by the prostate.
It is a highly tissue-specific marker in serum, but it only has minimal disease specificity. Although diagnostic improvements have been made through the use of PSA density, PSA velocity, and the PSA quotient, Prostata-spezifisches Antigen PSA diagnosis of prostate carcinoma by serum analysis is, nevertheless, accompanied by uncertainties.
A definitive diagnosis of prostate carcinoma can be made only after tumor Prostata-spezifisches Antigen PSA and histopathologic examination. Oxford University Press is a Prostata-spezifisches Antigen PSA of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide.
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