Testing bias in clinical databases: methodological considerations.
BACKGROUND
Laboratory testing in clinical practice is never a random process. In this study we evaluated testing bias for neutrophil counts in clinical practice by using results from requested and non-requested hematological blood tests.


METHODS
This study was conducted using data from the Utrecht Patient Oriented Database. This clinical database is unique, as it contains physician requested data, but also data that are not requested by the physician, but measured as result of requesting other hematological parameters. We identified adult patients, hospitalized in 2005 with at least two blood tests during admission, where requests for general blood profiles and specifically for neutrophil counts were contrasted in scenario analyses. Possible effect modifiers were diagnosis and glucocorticoid use.


RESULTS
A total of 567 patients with requested neutrophil counts and 1,439 patients with non-requested neutrophil counts were analyzed. The absolute neutrophil count at admission differed with a mean of 7.4 x 109/l for requested counts and 8.3 x 109/l for non-requested counts (p-value < 0.001). This difference could be explained for 83.2% by the occurrence of cardiovascular disease as underlying disease and for 4.5% by glucocorticoid use.


CONCLUSIONS
Requests for neutrophil counts in clinical databases are associated with underlying disease and with cardiovascular disease in particular. The results from our study show the importance of evaluating testing bias in epidemiological studies obtaining data from clinical databases.
Velthove
Karin J
KJ
Faculty of Science, Division of Pharmacoepidemiology and Pharmacotherapy, Utrecht Institute of Pharmaceutical Sciences, Utrecht University, The Netherlands. H.G.M.Leufkens@uu.nl.
Leufkens
Hubert Gm
HG
Souverein
Patrick C
PC
Schweizer
René C
RC
van Solinge
Wouter W
WW
Pharmacoepidemiol Drug Saf. 2004 Jul;13(7):437-41
15269927
Clin Chem Lab Med. 2007;45(1):13-9
17243908
Arch Intern Med. 1999 Jan 11;159(1):65-70
9892332
Lancet. 2006 Aug 26;368(9537):804-13
16935691
Exp Gerontol. 2004 Apr;39(4):615-9
15050297
J Clin Epidemiol. 2003 Jun;56(6):501-6
12873643
Eur J Epidemiol. 1999 Oct;15(9):773-81
10608355
Br Med J. 1968 Apr 27;2(5599):199-205
5653025
Clin Chem Lab Med. 2009;47(5):573-8
19397484
J Vasc Surg. 2005 Apr;41(4):610-7
15874924
Emerg Themes Epidemiol. 2009 Feb 27;6:2
19250518
Eur J Epidemiol. 2007;22(4):267-72
17342451
Circulation. 1989 Mar;79(3):549-56
2537159
Eur Respir J. 1998 Oct;12(4):820-4
9817152
J Clin Epidemiol. 2005 Apr;58(4):323-37
15862718
Med Care. 2007 Oct;45(10 Supl 2):S13-5
17909371
Emerg Themes Epidemiol. 2005 Sep 01;2:8
16137327
Am J Respir Crit Care Med. 1999 Nov;160(5 Pt 1):1532-9
10556116
J Chronic Dis. 1979;32(1-2):51-63
447779
Eur J Epidemiol. 2006;21(3):167-70
16547830
Pharmacoepidemiol Drug Saf. 2008 Jun;17(6):535-45
18265414
J Public Health Med. 1999 Sep;21(3):299-304
10528957
Eur Respir J. 1999 May;13(5):1198-208
10414427