Ausgehend von der Finite-Elemente-Methode — dem am häufigsten verwendeten numerischen Verfahren in der Strukturmechanik — und der Methode der Mehrkörpersimulation — zur Modellierung von mechanischen Systemen mit großen Starrkörperbewegungen — beschreibt der Beitrag Grundlagen und Methodik zur Kopplung beider Verfahren. Die Kombination führt auf eine Beschreibung als elastisches Mehrkörpersystem und erfordert meist eine Modellordnungsreduktion. Für diesen Zweck sind diverse Techniken in der hauseigenen Software MORPACK implementiert, deren Funktionalität am Beispiel des kommerziellen Finite-Elemente-Programmes ANSYS und des kommerziellen Mehrkörpersimulationsprogrammes SIMPACK vorgestellt wird.
The effect of sample collection, storage conditions (time and temperature), and freeze-thaw cycles on the stability of free prostate-specific antigen (fPSA), PSA complexed with α1-antichymotrypsin (ACT-PSA), and total PSA (tPSA) in serum was studied. The analytes were quantified using immunoassays for tPSA and fPSA on the Elecsys system 2010 and a research assay for ACT-PSA on the ES system (Roche Diagnostics). The stability of the analytes was calculated as percentages of the values measured in samples 1 h after blood collection. When the samples were stored at 37 °C, at room temperature or at 4 °C, the stability of ACT-PSA was less impaired than that of fPSA. To avoid erroneous results in the determination of PSA isoforms and their corresponding ratios, serum samples should be preserved at 4 °C when the analysis is performed within 8 h after blood collection, or they should be stored at −80 °C if the analysis is not feasible during that period.
Total prostate-specific antigen (PSA) and complexed PSA were determined in venous blood from 12 patients with prostate cancer before and after radical prostatectomy by using Immuno 1 PSA assays. The elimination kinetics of complexed PSA were compared with that of total PSA. Nearly constant concentrations of complexed PSA were found during the first six hours after surgery, in contrast to the rapid elimination of free PSA and the significant decrease of total PSA. From day one to ten there was a continuous and nearly identical decrease of complexed PSA compared to total PSA. Our findings suggest that the initial rapid decrease of free PSA immediately after operation could be caused by formation of new PSA-complex.
Prostate-specific antigen (PSA) assay-dependent variations could result in misinterpretation of individual PSA values. Therefore, the situation for clinical interpretation of PSA or percent free PSA (%fPSA) results is complicated. This review summarizes the differences in various total PSA (tPSA) and free PSA (fPSA) assays, and results obtained using the new World Health Organization (WHO) calibrated Access assays from various studies. Method comparisons between the traditionally calibrated Hybritech PSA and fPSA assays and the new “standardized” WHO calibrated assays yield results that are ∼25% lower for PSA and fPSA. A PSA cut-off of 3 or 3.1 μg/L should be considered for WHO calibrated assays in order to achieve the same sensitivity/specificity profile as with a cut-off of 4 μg/L in traditionally calibrated assays. The %fPSA cut-offs could be retained.
Background: The metrological traceability of prostate-specific antigen (PSA) assay calibration to WHO standards is desirable to potentially improve the comparability between PSA assays. A method comparison was performed between the traditionally standardized Beckman Coulter Hybritech Access PSA and free PSA (fPSA) assays and a new alternate calibration of assays aligned to the WHO standards 96/670 and 96/668, respectively.
Methods: Sera from 641 men with and without prostate cancer, various control materials and mixtures of different proportions of the WHO standards were measured with both assay calibrations.
Results: Excellent comparability between the corresponding assay calibrations was observed, with correlation coefficients of at least 0.996. The Passing-Bablok slopes were 0.747 for total PSA (tPSA), 0.776 for fPSA and 1.02 for the percentage ratio of fPSA to tPSA (%fPSA), while the corresponding percentages of the new WHO-aligned assay results related to the traditional assays were 76.2%, 77% and 102.2%. Receiver operating characteristics revealed no differences between the two PSA assay calibrations.
Conclusions: The WHO calibration yields results approximately 25% lower for tPSA and fPSA values when compared with the conventional Hybritech calibration. Using the WHO-aligned PSA assay, a tPSA cut-off of 3 μg/L should be considered in clinical practice, while %fPSA cut-offs could be retained.
Background: In 2013, thiosulfate in urine has been proposed as promising prostate cancer (PCa) biomarker. However, a missing comparison with other proven PCa markers suggested a re-evaluation study. Therefore, together with the authors from the initial study, the diagnostic accuracy of thiosulfate was compared with that of urinary prostate cancer associated 3 (PCA3), serum prostate health index (Phi), and percent free prostate-specific antigen (%fPSA). Thiosulfate was further measured in a multicenter approach to exclude center-related biases.
Methods: Thiosulfate, calculated as ratio of thiosulfate to urinary creatinine (TS/Crea ratio), was measured in two cohorts in a total of 269 patients. In the retrospective study (n=160) PCA3, Phi, PSA, and %fPSA were compared with the TS/Crea ratio between patients with and without PCa according to the prostate needle biopsy results. The second prospective cohort included 109 patients from four centers.
Results: The median TS/Crea ratio was not statistically different between the patients with and without PCa. The receiver-operating characteristics showed that the TS/Crea ratio was unable to discriminate between patients with and without PCa in contrast to %fPSA, Phi, and PCA3. In all four centers, the low median TS/Crea ratios (<1 mmol/mol) in both patient cohorts were confirmed and thiosulfate was again not able to distinguish between them (p-values, 0.13–0.90).
Conclusions: This study could not confirm the previously observed high median TS/Crea ratio in PCa patients in comparison to non-PCa patients. Thiosulfate subsequently failed as PCa biomarker while PCA3 and Phi showed the expected diagnostic improvement.