855 Definition of the Limit of Detection (LoD) for serum isoform [−2]proPSA in patients with recurrent prostate cancer after radical prostatectomy: An analytic study

Ceriotti F.1, Pontillo M.1, Fasoli L.1, Lazzeri M.2, Lughezzani G.2, Lista G.2, Larcher A.2, Cestari A.2, Buffi N.2, Fuzzi
G.3, Guazzoni G.2
1Ospedale San Raffaele, Laboraf - Diagnostica E Ricerca, Milan, Italy, 2Ospedale San Raffaele Turro, Dept. of
Urology, Milan, Italy, 3Istituto Ricerche Cliniche "M. Fanfani", Diagnostica Clinica, Florence, Italy
INTRODUCTION & OBJECTIVES: The PSA sensitivity for detecting biochemical recurrence (BCR) after radical
prostatectomy (RP), defined as two consecutive values of tPSA >0.2 ng/mL, is directly related to the sensitivity of the
PSA assay. The accuracy of ultrasensitive PSAs (uPSA), with a detection limit of 0.001 ng/ml, remains contradictory.
As serum isoform [-2] proPSA (p2PSA) is normally expressed in pg/mL, it may be more sensitive than PSA and uPSA
at detecting early recurrence in patients after RP. The aim of this study was to test the Limit of Detection (LoD) for
p2PSA using sera from patients with proven recurrent prostate cancer (PCa) after RP.
MATERIAL & METHODS: The blood sample of 10 patients with histologically proven PCa recurrence after RP with a
tPSA > 0.2 ng/ml and < 4ng/mg were collected before the start of any secondary treatment. Five of the samples were
stored at -80°C and the other 5 samples at -20° C. One aliquot of each sample was measured to confirm the PSA
value at entry and each sample was diluted with a PSA free serum in order to obtain a tPSA result of about 0.2 ng/mL.
Diluted sera were frozen again at -80° C° and subsequently, each day, one aliquot per sample was thawed and -
2proPSA was measured in duplicate. The primary objective was to detect the LoD according to the CLSI (Clinical and
Laboratory Standards Institute) EP17-A protocol (LoD = LoB + Cβ * cumulative SD (where LoB is limit of Blank (0.5
pg/mL) and Cβ is 95th percentile of the standard Gaussian distribution corrected = 1.645/(1-1(4 x f) [f = degrees of
freedom = 90])).
RESULTS: Table one summarises the baseline results and table 2 the p2PSA results after dilution. We obtained
consistent results for p2PSA with a limit of detection of 0.8 pg/mL ± SD 0.1979 pg/mL in all diluted samples. No
difference was observed for samples stored at -80°C or -20° C.
Table 1
855 Definition of the Limit of Detection (LoD) for serum isoform [-2]proPSA
in patients with recurrent prostate cancer after radical prostatectomy:
An analytic study
Eur Urol Suppl 2013;12;e855
PT PSA (ng/mL) Free PSA (ng/mL) f/tPSA p2PSA (pg/mL) Dilution ratio Total PSA after dilution
1 4.88 1.83 0.38 68.23 1:24.4 0.19
2 1.2 0.06 0.05 3.16 1:6 0.19
3 0.67 0.03 0.05 2.24 1:3.4 0.21
4 4.27 1.29 0.3 23.78 1:21.35 0.21
5 2.72 0.19 0.07 2.63 1:13.6 0.20