title: Between-method differences in prostate-specific antigen assays affect prostate cancer risk prediction by nomograms.
abstract: BACKGROUND
  To date, no published nomogram for prostate cancer (PCa) risk prediction has considered the between-method differences associated with estimating concentrations of prostate-specific antigen (PSA).
  
  
  METHODS
  Total PSA (tPSA) and free PSA were measured in 780 biopsy-referred men with 5 different assays. These data, together with other clinical parameters, were applied to 5 published nomograms that are used for PCa detection. Discrimination and calibration criteria were used to characterize the accuracy of the nomogram models under these conditions.
  
  
  RESULTS
  PCa was found in 455 men (58.3%), and 325 men had no evidence of malignancy. Median tPSA concentrations ranged from 5.5 μg/L to 7.04 μg/L, whereas the median percentage of free PSA ranged from 10.6% to 16.4%. Both the calibration and discrimination of the nomograms varied significantly across different types of PSA assays. Median PCa probabilities, which indicate PCa risk, ranged from 0.59 to 0.76 when different PSA assays were used within the same nomogram. On the other hand, various nomograms produced different PCa probabilities when the same PSA assay was used. Although the ROC curves had comparable areas under the ROC curve, considerable differences were observed among the 5 assays when the sensitivities and specificities at various PCa probability cutoffs were analyzed.
  
  
  CONCLUSIONS
  The accuracy of the PCa probabilities predicted according to different nomograms is limited by the lack of agreement between the different PSA assays. This difference between methods may lead to unacceptable variation in PCa risk prediction. A more cautious application of nomograms is recommended.
authors: Department of Urology, Charité - Universitätsmedizin Berlin, Berlin, Germany. carsten.stephan@charite.de
authors: Carsten
authors: C
authors: Stephan
authors: Kerstin
authors: K
authors: Siemssen
authors: Henning
authors: H
authors: Cammann
authors: Frank
authors: F
authors: Friedersdorff
authors: Serdar
authors: S
authors: Deger
authors: Mark
authors: M
authors: Schrader
authors: Kurt
authors: K
authors: Miller
authors: Michael
authors: M
authors: Lein
authors: Klaus
authors: K
authors: Jung
authors: Hellmuth-Alexander
authors: HA
authors: Meyer