effective pre screen strategy in postmenopausal women above 65 years in primary care settings, with savings of 22€ per osteoporosis women diagnosed.
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COST EFFECTIVENESS ANALYSIS OF REFERRAL FOR DUAL ENERGY X-RAY ABSORPTIOMETRY (DXA) USING QUANTITATIVE BONE ULTRASOUND AS A PRE-SCREENING TOOL IN POSTMENOPAUSAL WOMEN.
ECOGRAFIA OSEA EN ATENCION PRIMARIA
F. Marín1, J.A. Sacristán1, A. Díez-Pérez2, C. Carbonell3, M. Abizanda4, R.M. Alcolea5, A. Cervera4, C. Olmos3, T. Rama5, E. Galindo5, A. Cama3. 1
Dept. Medical Research, Lilly S.A., Madrid; 2Internal Medice Dept. Hospital del Mar; 3ABS Vía Roma; 4CAP Gran Vía; 5ABS Llefiá; Barcelona, Spain. INTRODUCTION AND OBJETIVE:
MEASUREMENTS:
It has been suggested that quantitative bone ultrasound (QUS) could be used as a population pre-screen, to maximize the cost effectiveness of referral for DXA assessment of BMD (Glüer et al. Osteoporos Int 1999:9;193).
Bone Mineral Density (BMD) at the femoral neck was evaluated by centralized DXA (Hologic 4500 SL), and heel QUS using SaharaTM (Hologic).
We analyzed how such an approach might perform in the assessment of postmenopausal women from the general population.
STATISTICAL ANALYSIS: • The likelihood ratio for a positive result (diagnosis of osteoporosis by femoral neck BMD according to the WHO criteria) = LR(+) = sensitivity / [1 - specificity]. • The likelihood ratio for a negative result = LR(-) = [1 - sensitivity]/specificity.
PATIENTS AND METHODS: 267 Caucasian women ≥ 65 years (mean ± SD: 72.3 ± 5.3), without neoplastic or metabolic bone diseases, who were consecutively attended for any medical reason in three Primary Care Centers in the metropolitan area of Barcelona between March and October 2000 (Non-probabilistic sampling of consecutive cases).
Applying positive (LR + > 5) and negative (LR - < 0,2) likelihood ratios, we established thresholds for diagnosis of osteoporosis or non-osteoporosis for the different QUS variables, and at an Estimated heel BMD T-scores when measured against DXA.
COSTS: Average local costs for DXA scan (90 €), and estimated QUS scan (6 €) were applied to calculate the cost for a correctly identified osteoporotic subject.
RESULTS: Given the results of the LRs ratios (Table 1), we established thresholds for diagnosis of osteoporosis or non-osteoporosis at an Estimated heel BMD Tscores of -2,50 SD and +0,05 SD respectively, when measured against DXA. The sensitivity of this threshold for the diagnosis of osteoporosis was of 97% (Table 1). 149 (55.8%) of the women had a femoral neck T-score ≤ -2.50 SD. The Estimated heel BMD T-score thresholds avoided the need for DXA referrals in 59 (22.1%) of the women, either because they were below the LR(+) threshold (osteoporosis: 12%) or above the LR(-) threshold (non-osteoporosis: 10.1%) (Figure 1).
Table 1. Performance of the different QUS parameters for osteoporosis screening. QUS parameter No-osteoporosis
95.5
99
5
0.13
6/7
Osteoporosis
42.0
18
97
5.28
27/31
No-osteoporosis
1579
98
12
0.17
14/17
Osteoporosis
1490
16
97
5.99
23/26
No-osteoporosis
115.6
99
9
0.14
11/13
Osteoporosis
60.3
21
96
5.02
32/37
BUA (db/MHz)
14.2
SOS (m/sec)
114 out of the 208 women referred for DXA assessment (54.8%) were classified as osteoporotic by the WHO criteria. The cost per osteoporotic subject identified based on DXA measurement alone was 161 € (Table 2).
Cut-off Sensitivity Specificity Likelihood Cases % of cases value* CCC/TCC¥ excluded (%) (%) ratio§ for DXA
16.1
QUI (%)
18.7
The cost per osteoporotic subject identified using QUS as a pre-screen with defined thresholds of the Estimated heel BMD T-scores was 139 € (Table 2).
Estimated Heel No-osteoporosis BMD (g/cm2) Osteoporosis
0.650
98
10
0.14
11/13
0.305
21
97
6.34
32/36
Figure 1. Osteoporosis screening workout in our study population using Estimated Heel BMD T-score values. Women are classified as non-osteoporotic (normal or osteopenic), osteoporotic and uncertain, in whom a DXA measurement should be taken to make an accurate diagnosis.
Estimated Heel No-osteoporosis BMD T-score Osteoporosis
+0.05
97
18
0.18
22/27
-2.5
22
94
5.48
28/32
18.4
22.1
* First value yielding a LR (+) ≥5 for a positive test, and first value yielding a LR (-) ≤0.2 for a negative test 0.2 refer to a negative likelihood ratio. § Values above 5 refer to a positive likelihood ratio; values below ¥ CCC = correctly classified cases; TCC = total classified cases.
Table 2. Cost-effectivity per osteoporotic women correctly identified with the two diagnosis work-up strategies.
Postmenopausal Women n = 267
Quantitative Heel Ultrasound Est. Heel BMD T-score
a) Cost-effectivity (CEA) of all referred DXA scans (CA) divided by the number of true positive osteoporotic women identified (EA): CEA = CA / EA = [267 * 90]€ / 149 = 161 €
+0.05 or above n = 27 (10.1%)
+0.04 to –2.49 n = 208 (77.9%)
-2.50 or below n = 32 (12%)
Non-osteoporosis
Uncertain (Measure BMD by DXA)
Osteoporosis
Non-osteoporosis n = 94 (35.2%)
b) Cost-effectivity (CEB) of screening with QUS to all patients plus DXA scans in patients with uncertain Estimated Heel BMD T-score (CB) divided by the number of true positive osteoporotic women identified (EB): CEB= CB / EB = [[267 * 6] € + [208 * 90] €] / 146 = 139 €
Osteoporosis n = 114 (42.6%)
c) Incremental costs for the additional cases diagnosed with DXA vs QUS (CI): CI = [CA – CB] / [EA – EB] = 1236 €
CONCLUSION:
Our results suggest that applying strict Estimated heel BMD T-score thresholds in screening for osteoporosis with QUS, may be a cost effective pre screen strategy in postmenopausal women above 65 years in primary care settings, with savings of 22€ per osteoporosis women diagnosed. It seems likely that if QUS measurements are combined with clinical risk factors for osteoporosis and future fracture, the effectiveness of the technique as a screening tool will be substantially improved. Acknowledgment: This research was supported by a Grant of the Medical Research Department, Eli Lilly and Company, Spain. Angel Pérez Romero and Elena Arriaza; Medical Research Department, Eli Lilly and Company, coordinated the study. The statistical analysis was performed by Joan Vila and Jaume Marrugat, Institut Municipal d’Investigació Mèdica, and the Universitat Autónoma, Barcelona.
