Technical ReportClinimetric properties of the EuroQol-5D in patients with chronic low back pain
Introduction
The EuroQol-5D (EQ-5D) [1] is a widely used instrument to assess health-related quality of life (QOL). It is used in cost-effectiveness research based on quality-adjusted life year (QALY) and is recommended by the Dutch Healthcare Insurance Board [2]. Pain, disability, and functional status may affect QOL differently for various diseases. Consequently, the clinimetric properties of EQ-5D may vary according to the disease studied. Interventions for patients with nonspecific chronic low back pain (CLBP) aim to reduce disability and improve functioning and participation, which in turn should be related to QOL. Consequently, EQ-5D should be related to (changes in) functioning and disability to be a valid measure of QOL in patients with CLBP. Clinimetric properties for these specific purposes of EQ-5D have been studied scarcely in the field of CLBP.
It is known that lower QOL is associated with efficiency loss and absenteeism in patients with low back pain [3]. Another study addressed the assumption of relatedness between QOL and functioning and found differences in the responsiveness of EQ-5D in studies among different diseases and countries. Hence, the primary outcome of the therapy does not always relate to QOL in the same manner. Consequently, specific regression coefficients (tarrifs) were constructed for different countries [4], [5]. Responsiveness of the EQ-5D was found to be moderate in a study in which exercise treatment was provided [6] and was sufficient for patients undergoing low-back surgery (area under the receiver operating characteristics [ROC] curve (AUC) of 0.77) [7]. One study reported the differences between pain, disability, and QOL after spinal surgery [8]. In general, responsiveness of the EQ-5D appeared higher in acute back care than in CLBP [6], [7], [9]. To make valid decisions concerning QALYs, however, the primary outcome measure between interventions should be similar, namely QOL. The relation of QOL to reported disability, pain, or functioning should therefore be similar between different diseases. It is, however, unknown if EQ-5D correlates sufficiently with these primary outcomes. Additionally, there is insufficient data concerning responsiveness and minimal clinically important change (MCIC) in a broad perspective of CLBP interventions. The objectives of this study were to test criterion validity, responsiveness, and MCIC of the EQ-5D in patients with CLBP.
Section snippets
Procedures
The Groningen Spine Center is a secondary and tertiary care multidisciplinary center for patients with spinal disorders, that is, part of the University Medical Center Groningen, in the Netherlands. Disciplines involved were one or more of the following: rehabilitation medicine, neurology, and anesthesiology. Interventions were chosen based on medical status and patient preference and included outpatient multidisciplinary rehabilitation with psychology, physiotherapy, and occupational therapy
Results
Data of 151 patients were analyzed. Fifty-three percent received a minimal intervention, 27% rehabilitation, 19% anesthesiology (injections or medication), and 2% of the patients received a combination of treatments. Baseline characteristics are presented in Table 1. At baseline, no patient reached the ceiling or floor of the EQ-5D. At T1, a ceiling score was reached by six patients (4%). At baseline, 15% had one or more missing items on the PDI and 13% on the RMDQ and at T1, 21% had one or
Discussion
The main purpose of this study was to determine the clinimetric properties of the EQ-5D in patients with nonspecific CLBP. From the data of this study, the criterion validity of EQ-5D was confirmed. Responsiveness of EQ-5D is borderline sufficient (AUC=0.71). For the EQ-5D, a small OCP of 0.03 points was found, meaning that a change of 0.03 points in QOL is related to a change on the GPE with a sensitivity of 0.73 and specificity of 0.66. In clinical practice, this finding means that any
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Author disclosures: RS: Research Support (Investigator Salary): University of Groningen (D); Research Support (Staff/Materials): University of Groningen (D). MFR: Nothing to disclose. BLGNS: Nothing to disclose. MHC: Nothing to disclose. PCAJV: Royalties: Publisher de Tijdstroom (A); Consulting: Boehringer (A); Speaking/Teaching Arrangements: Boehringer (A).
The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com.