|Effect of D-dimer testing on the diagnostic strategy of suspected pulmonary embolism: an observational study of practice patterns and costs
|Lebrun E, Maitre B, Grenier-Sennelier C, Katsahian S, Gouault-Heilmann M, Vasile N, Meignan M, Housset B, Durand-Zaleski I
This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn.
The use of D-dimer testing for the diagnosis of suspected pulmonary embolism.
Economic study type
The study population comprised patients admitted to the emergency room and diagnosed with suspected pulmonary embolism. No other exclusion criteria were reported.
The setting was a tertiary care centre. The economic analysis was carried out in France.
Dates to which data relate
The dates during which the effectiveness, resource use and cost data were gathered, and the price year were not reported.
Source of effectiveness data
The effectiveness data were derived from a single study.
Link between effectiveness and cost data
The costing was carried out prospectively on the same patient sample as that used in the effectiveness analysis.
Five hundred and twenty-four patients were enrolled in the study during a 7-month period. The demographic characteristics of the patients were not reported. No power calculations were performed to determine sample size.
The study took the form of an unblinded diagnostic test evaluation, and was carried out at a single centre. The patients were followed-up during their entire hospital stay. The follow-up was continued after discharge in cases where the diagnosis had not been ascertained earlier. No patient was lost to follow-up.
Analysis of effectiveness
The primary health outcomes were the positive and negative predictive values, and the percentage of patients assigned a different treatment strategy following the D-dimer result.
A total of 541 D-dimer assays were requested for 524 patients.
Sixty patients were diagnosed with pulmonary embolism and 454 with other diagnoses.
The D-dimer test was negative in 165 patients. Of these, 87% were not tested further for pulmonary embolism, compared with 44% of those with a positive test.
The positive predictive value was 16% and the negative predictive value was 99%.
Treatment was started in 9% of the patients, before the results of the D-dimer test were available in 9% of the patients. Treatment was altered in 0.6% of the patients following the D-dimer results, and in 5% of the patients following the imaging results.
The authors argued that the use of D-dimers may have been effective in reducing the number of imaging tests prescribed.
Measure of benefits used in the economic analysis
The authors did not derive a measure of benefit. The analysis was therefore categorised as a cost-consequences analysis.
The direct costs were not discounted due to the short timeframe of the study (less than 1 year). The quantities and unit costs per diagnostic test were reported separately. The unit costs were the costs of reagents, supplies, medical and nonmedical labour, equipment amortisation, building depreciation, and overheads. The authors estimated both the total and marginal costs. To calculate marginal costs, the authors assumed that personnel costs, machine rental, depreciation, amortisation, and all overhead costs were fixed. The quantity/cost boundary adopted was that of the hospital. The source of the cost data and the price year were not reported.
Statistical analysis of costs
No statistical analysis of costs was performed.
The indirect costs were not included.
No sensitivity analyses were reported.
Estimated benefits used in the economic analysis
See 'Effectiveness Results' section.
For a population of 100 patients, the D-dimer test cost 3,000 Euros and saved 4,982 Euros. When only marginal costs were considered, the net benefit of D-dimer testing was 4 Euros per patient.
Synthesis of costs and benefits
The authors argued that the use of D-dimer testing may have been effective in reducing the number of imaging tests, and may be beneficial to the hospital.
CRD COMMENTARY - Selection of comparators
The major flaw in this study was that the decision-making process for each diagnostic test was not reported. Therefore, the precise strategy against which the D-dimer assay was being compared was unknown.
Validity of estimate of measure of effectiveness
The analysis was based on an unblinded diagnostic test evaluation. This was inappropriate for the study question, since the test results on which the decision to test or treat was based were unknown. The sample size was not reported. The authors did not report the baseline characteristics of the study sample. Hence, it was difficult to assess whether the study sample was representative of the study population.
The measures of effectiveness were ostensibly appropriate, particularly in terms of the effect on treatment decisions. In order to judge the usefulness of the D-dimer assay, it would be necessary to know precisely which decisions were made using which strategies, and whether or not these strategies included the D-dimer assay. All that was reported, however, was the percentage of treatments started or altered after the D-dimer or imaging results. Knowing the result of one test before making the next decision is clearly a different diagnostic strategy to that of making a decision when not knowing the result.
Validity of estimate of measure of benefit
The number of clinically suspected pulmonary emboli was estimated directly from the effectiveness analysis.
Validity of estimate of costs
The cost analysis included all the relevant direct cost categories. In addition, it reported the quantities and costs separately, and reported both the total and marginal costs. However, no statistical or sensitivity analyses were reported on costs, and the source of the cost data was not reported. The price year was not reported either, which makes reflation exercises in other settings more difficult
The authors made appropriate comparisons of their findings with those from other studies, but did not address the issue of generalisability to other settings. As stated, several important results were not given. The study considered patients with suspected pulmonary emboli and this was reflected in the authors' conclusions. The dates during which effectiveness, resource use and cost data were gathered were not reported.
Implications of the study
The authors argued that the use of D-dimer testing may have been effective in reducing the number of imaging tests, and may be beneficial to the hospital. However, they also stated that because this was an observational study, no definitive conclusions could be reached about the effect of introducing D-dimer testing on the number of imaging tests prescribed. The value of the D-dimer assay cannot be deduced from the results presented.
Lebrun E, Maitre B, Grenier-Sennelier C, Katsahian S, Gouault-Heilmann M, Vasile N, Meignan M, Housset B, Durand-Zaleski I. Effect of D-dimer testing on the diagnostic strategy of suspected pulmonary embolism: an observational study of practice patterns and costs. European Radiology 2000; 10(Supplement 3): S433-S434
Subject indexing assigned by NLM
Clinical Laboratory Techniques /economics; Europe; Fibrin Fibrinogen Degradation Products /analysis; Humans; Pulmonary Embolism /diagnosis /economics; Sensitivity and Specificity
Date bibliographic record published
Date abstract record published