Measurement of Circulating Forms of
Prostate-specific Antigen in Whole Blood
Immediately after Venipuncture:
Implications for Point-of-Care Testing
Timo Piironen,
1
Martti Nurmi,
3
Kerttu Irjala,
4
Olli Heinonen,
5
Hans Lilja,
6
Timo Lo ¨ vgren,
2
and Kim Pettersson
2*
Background: The purpose of this study was to validate
the use of whole-blood samples in the determination of
circulating forms of prostate-specific antigen (PSA).
Methods: Blood samples of hospitalized prostate cancer
and benign prostatic hyperplasia patients were collected
and processed to generate whole-blood and serum sam-
ples. Three different rapid two-site immunoassays were
developed to measure the concentrations of total PSA
(PSA-T), free PSA (PSA-F), and PSA-
1
-antichymotryp-
sin complex (PSA-ACT) to detect in vitro changes in
whole-blood samples immediately after venipuncture.
The possible influence of muscle movement on the
release of PSA from prostate gland was studied in
healthy men by measuring the rapid in vitro whole-
blood kinetics of PSA forms before and after 15 min of
physical exercise on a stationary bicycle.
Results: Rapid PSA-T, PSA-F, and PSA-ACT assays
were designed using a 10-min sample incubation. No
significant changes were detected in the concentrations
of PSA-T, PSA-F, and PSA-ACT from the earliest time
point of 12–16 min compared with measurements per-
formed up to 4 h after venipuncture. Physical exercise
did not influence the concentrations of the circulating
forms of PSA. Hematocrit-corrected whole-blood values
of PSA-T and PSA-F forms were comparable to the
respective serum values. Calculation of the percentage
of PSA-F (PSA F/T ratio 100) was similar irrespective
of the sample format used, i.e., whole blood or serum.
Conclusions: We found that immunodetectable PSA
forms are likely at steady state immediately after veni-
puncture, thus enabling the use of anticoagulated
whole-blood samples in near-patient settings for point-
of-care testing, whereas determinations of PSA (e.g.,
PSA-T, PSA-F, or PSA-ACT) performed within the time
frame of the office visit would provide results equiva-
lent to conventional analyses performed in serum.
© 2001 American Association for Clinical Chemistry
During the past 15 years, the immunochemical detection
of prostate-specific antigen (PSA)
7
has become an indis-
pensable prostate cancer (PCa) marker. In addition to the
established use of PSA for monitoring disease progres-
sion, increasing interest has been directed toward the
potential of PSA for early detection of PCa. Population-
based screening for PCa in the absence of definitive
evidence for the clinical usefulness of PSA remains a
controversial issue (1). Despite this, the use of PSA testing
as part of regular physical check-ups has led to an
increase in the reported number of cases of PCa in both
symptomatic and nonsymptomatic urology patients.
PSA is a 28.4-kDa glycoprotein that consists of 237
amino acids (2). It is a chymotrypsin-like serine protease
and a member of the glandular kallikrein family (3).
1
The Finsen Laboratory af.sn. 8621, Strandboulevarden 49, 2100 Copen-
hagen, Denmark.
2
Department of Biotechnology and
5
Paavo Nurmi Center, University of
Turku, 20520 Turku, Finland.
3
Department of Surgery, Turku University Central Hospital, 20520 Turku,
Finland.
4
Department of Clinical Chemistry, Turku University Central Hospital,
20520 Turku, Finland.
6
Department of Laboratory Medicine, Division of Clinical Chemistry,
Lund University, University Hospital, 20502 Malmo ¨ , Sweden.
*Author for correspondence. Fax 358-2-3338050; e-mail kim.pettersson@
utu.fi.
Received in revised form January 3, 2001; accepted January 19, 2001.
7
Nonstandard abbreviations: PSA, prostate-specific antigen; PCa, prostate
cancer; ACT,
1
-antichymotrypsin; AMG,
2
-macroglobulin; PSA-F, free PSA;
BPH, benign prostatic hyperplasia; PSA-T, total immunoreactive PSA; and
MAb, monoclonal antibody.
Clinical Chemistry 47:4
703–711 (2001)
Enzymes and Protein
Markers
703