PSA assay of dried blood samples from the ear lobe on a filter paper with special reference to prostatic mass screening

Prostate-specific antigen assay using whole blood samples spotted on filter paper and its application to mass screening for prostate cancer

AIM

The disc assay system for prostate-specific antigen (PSA) is a novel technique using a small amount of whole blood on filter paper. The accuracy of this assay system and its feasibility for use in prostate cancer mass screening were evaluated.

METHODS

In the first arm of the study, to evaluate the accuracy of the disc assay system, PSA values were determined by both a disc assay system and a standard serum assay system using the same blood samples obtained from 420 outpatients. In the second arm of the study, the feasibility and reliability of the disc assay system were examined in prostate cancer mass screening. A total of 2475 men were screened by the disc assay (disc group) and 3348 men were screened by the standard serum assay (serum group) in the first step of mass screening. In the second step of the screening in the disc group, 101 men underwent PSA tests by a standard serum assay, then the first PSA values determined by the disc assay were compared with the second PSA values determined by the standard serum assay. In the second step of the screening in the serum group, 94 men underwent additional PSA tests by a serum assay, and then the first PSA values were compared with the second PSA values. Two men in each group were excluded from analysis because the true PSA values of the first step were not available (more than 50 ng/mL).

RESULTS

The PSA values determined by the disc assay closely correlated with those obtained by the standard assay (r = 0.987) in 295 outpatients with PSA levels between 1.0 and 20 ng/mL. In the PSA mass screening, the PSA values determined in the first step closely correlated with those in the second step both in the disc group (r = 0.916) and in the serum group (r = 0.845). A significant dissociation of the two PSA values was observed in seven of 99 men in the disc group and in three of 92 men in the serum group. However, there was no statistical significance in the incidence of dissociation in the two PSA values between the disc group and the serum group.

CONCLUSIONS

The disc assay system seems to be a sensitive and accurate assay system. The feasibility and reliability of the disc assay system were well demonstrated in the field during prostate cancer mass screening.

Relevance of the prostate-specific antigen (PSA) nanotest compared to the classical PSA test in the organized mass screening of prostate cancer

OBJECTIVE

To assess the reliability of a new measurement of prostate-specific antigen (PSA) using a blotting-paper assay (nanotest) compared to the standard PSA immunoassay.

SUBJECTS AND METHODS

The PSA level was measured in 205 men volunteers (median age 70 years, range 41-75) using a nanotest and a standard PSA immunoassay, collected at the same time; 30 microL of capillary blood placed on to a blotting paper were collected for the nanotest and sent by mail to the same laboratory for the two assays. The results were compared statistically using the Spearman test, the intraclass correlation coefficient and the Bland-Altman test.

RESULTS

The nanotest threshold for an abnormal PSA level was 78 pg/mL, which corresponded to a standard PSA value of 3 ng/mL, with a sensitivity of 100%. There was a significant correlation (r = 0.98, Spearman test; P < 0.001) between the nanotest and the standard PSA assay. The intraclass correlation coefficient was 0.87. The Bland-Altman test showed a good agreement between the nanotest and the standard PSA assay, but there was an increasing proportional difference with increasing PSA value.

CONCLUSION

There was a very high correlation between the nanotest and the standard PSA assay, especially for standard PSA levels of <5 ng/mL. Economic and clinical studies are indicated to confirm the utility of the nanotest in organized mass screening of prostate cancer.

Progression of prostatic cancer in relation to age in patients detected by mass screening program

With the aim of revealing the natural history of prostatic cancer, the distribution of age was examined in relation to disease progression in patients detected by mass screening programs. Between 1975 and 1996, such programs detected a total number of 132 patients with prostatic cancer. The mean ages of patients with Stage B, Stage C and Stage D disease were 71.2, 73.8 and 75.3 years, respectively. This might suggest that the difference of 3 years in mean age between Stage B and Stage C disease reflects the time interval of the progression of prostatic cancer from the early (Stage B) to the advanced (Stage C) stage. These results coincided well with the natural history of prostatic cancer, which we proposed previously based upon the "size of ranking" analysis of latent prostatic cancer and doubling time obtained from ultrasonic measurement of prostatic volume. An epidemiological study of prostatic cancer detected by mass screening would offer data of value for the elucidation of the natural history of that disease.

The role of prostatic planimetry using transrectal sonography in prostatic diseases

Transrectal sonography (TRS) remains the best method for prostatic planimetry, providing much information of value for the diagnosis and treatment of prostatic diseases, particularly of prostatic cancer. Currently, TRS is a routine tool in the detection and treatment of prostatic cancer. Prostatic planimetry is also available for a better understanding of elevated prostate-specific antigen (PSA). PSA indices modified by prostatic volume are applicable to the detection of prostatic cancer. The most critical application of prostatic planimetry is in monitoring prostatic cancer after treatment. Prostatic volume decreased exponentially after androgen deprivation therapy without exception in patients with prostatic cancer. The parameter "tau" (Tau), calculated from kinetic analysis based on sequential planimetric volumetry using TRS after the initiation of treatment, is a reliable prognosticator in an individual patient. Furthermore, tau predicts the manner of disease progression, and local or metastatic progression. Thus, transrectal ultrasonic prostatic planimetry is of special value in prostatic cancer.

Transrectal ultrasonic planimetry of the prostate in relation to age and lower urinary tract symptoms among elderly men in Japan

The aim of the present study is to correlate transrectal ultrasonic planimetric parameters of the prostate in relation to age and urinary symptoms as evaluated by the American Urological Association (AUA) symptom index score for benign prostatic hyperplasia (BPH). In 647 examinees on a mass screening program for prostatic diseases using transrectal sonography (TRS) in Japan, prostatic volume, transition zone volume, transition zone index (transition zone volume/prostatic volume) and presumed circle area ratio (PCAR) were determined using transrectal ultrasonic planimetry and compared with age and AUA symptom score. Increase in age, prostatic volume, transition zone volume and PCAR were significantly correlated with AUA symptom score. However, multiple regression analysis demonstrated that age and PCAR were the only significant independent determinant of symptom score. In particular, PCAR was the only significant determinants of symptom score in men with an intermediately enlarged prostate (20-30 ml in volume). The most significant difference in AUA symptom score was found between subgroups divided by PCAR with a cutoff point of 0.8. Among the planimetric parameters obtained by TRS, PCAR was the most powerful for evaluating BPH in terms of the severity of lower urinary tract symptoms.

Polypropylene fibre web, a new matrix for sampling blood for immunodiagnosis of schistosomiasis

Blood sampling on filter paper is widely used for immunodiagnostic and epidemiological purposes. However, elution of conventional filter papers impregnated with sera containing Schistosoma mansoni circulating anodic antigen (CAA) recovered only a small fraction of the antigen, thereby reducing the sensitivity of the assay. Polypropylene-based non-woven fibre web is a new sampling material with a low density of fibres and with a small surface area of contact. When it was impregnated with serum containing CAA, approximately 90% of the antigen could be extracted. The yield of antibodies against S. mansoni from the new sampling material did not differ from that from conventional filter papers.