Intra-individual short-term variability of prostate-specific antigen and other kallikrein markers in a serial collection of blood from men under evaluation for prostate cancer.
METHODS
Diagnostic (exploratory cohort).


METHODS
2b.


OBJECTIVE
To assess variation of total prostate-specific antigen (tPSA), free PSA (fPSA), percent fPSA, human glandular kallikrein 2 (hK2) and intact PSA measured three times within 2 weeks. Knowledge of the variation in an individual's PSA level is important for clinical decision-making.


METHODS
Study participants were 149 patients referred for prostate biopsy, of which 97 had benign disease and 52 had prostate cancer. Three blood samples were drawn with a median of 4 h between first and second samples and 12 days between first and third samples. Variability was described by absolute differences, ratios and intra-individual coefficients of variation. Total PSA, fPSA, hK2 and intact PSA were measured in anticoagulated blood plasma.


RESULTS
At baseline, the median tPSA was 6.8 (interquartile range, 4.5-9.6) ng/mL. The intra-individual variation was low for all biomarkers, and lowest for tPSA. For 80% of participants, the ratio between first and second time points for tPSA was in the range 0.91-1.09 and the ratio for percent fPSA was in the range 0.89-1.15. Total coefficients of variation between time 1 and 2 for tPSA, fPSA, percent fPSA, hK2 and intact PSA were 4.0%, 6.6%, 6.0%, 9.2% and 9.5%, respectively. The measurements taken several days apart varied more than those taken on the same day, although the variation between both time points was not large.


CONCLUSIONS
The intra-individual variation for all the kallikrein-like markers studied was relatively small, especially for samples drawn the same day. Few cases are reclassified between the time points. This indicates the high short-term biological and technical reproducibility of the tests in clinical use.
Division of Nephrology, Department of Clinical Sciences, Lund University, University Hospital, Malmö, Sweden. anders.christensson@med.lu.se
Anders
A
Christensson
Laila
L
Bruun
Thomas
T
Björk
Angel M
AM
Cronin
Andrew J
AJ
Vickers
Caroline J
CJ
Savage
Hans
H
Lilja
D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000097:blood*; D001707:Biopsy, Needle; D015331:Cohort Studies; D006801:Humans; D007610:Kallikreins / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D015588:Observer Variation; D017430:Prostate-Specific Antigen / Q000097:blood*; D011471:Prostatic Neoplasms / Q000097:blood* / Q000473:pathology*; D012680:Sensitivity and Specificity; D013548:Sweden; D013997:Time Factors
D014408:Biomarkers, Tumor; D007610:Kallikreins; D017430:Prostate-Specific Antigen