Methodologic standards for diagnostic test research in pulmonary medicine

A systematic review finds that diagnostic reviews fail to incorporate quality despite available tools

BACKGROUND AND OBJECTIVE

To review existing quality assessment tools for diagnostic accuracy studies and to examine to what extent quality was assessed and incorporated in diagnostic systematic reviews.

METHODS

Electronic databases were searched for tools to assess the quality of studies of diagnostic accuracy or guides for conducting, reporting or interpreting such studies. The Database of Abstracts of Reviews of Effects (DARE; 1995-2001) was used to identify systematic reviews of diagnostic studies to examine the practice of quality assessment of primary studies.

RESULTS

Ninety-one quality assessment tools were identified. Only two provided details of tool development, and only a small proportion provided any indication of the aspects of quality they aimed to assess. None of the tools had been systematically evaluated. We identified 114 systematic reviews, of which 58 (51%) had performed an explicit quality assessment and were further examined. The majority of reviews used more than one method of incorporating quality.

CONCLUSION

Most tools to assess the quality of diagnostic accuracy studies do not start from a well-defined definition of quality. None has been systematically evaluated. The majority of existing systematic reviews fail to take differences in quality into account. Reviewers should consider quality as a possible source of heterogeneity.

Diagnostic value of C-reactive protein in exudative pleural effusions

BACKGROUND: Tests able to help in the diagnostic work-up of pleural exudates are needed. C-reactive protein (CRP) may be useful for distinguishing between benign and malignant exudates. METHODS: A total of 123 consecutive patients diagnosed as having exudative pleural effusion (60 associated with malignancy and 63 benign effusions) were included in the study. Sensitivity, specificity, positive and negative predictive values (PV+, PV-), and positive and negative likelihood ratios (LR+, LR-) were established at different cut-off points. RESULTS: Pleural fluid CRP level was 23+/-12 mg/l (mean+/-S.D.) in pleural exudates associated with malignancy and 50+/-33 mg/l in benign effusions (P<0.001). With a cut-off point below 20 mg/l for malignancy, sensitivity of CRP was 0.50, specificity 0.89, PV+ 0.81, PV- 0.65, LR+ 4.50, and LR- 0.65. With a cut-off point above 45 mg/l for benign diseases, sensitivity was 0.44, specificity 0.95, PV+ 0.90, PV- 0.62, LR+ 8.89, and LR- 0.58. CONCLUSIONS: The pleural CRP level provides useful information for the study of pleural exudates. A level below 20 mg/l suggests a malignant origin and a level above 45 mg/l virtually rules out this possibility. Additional advantages of measuring CRP level are that it is an inexpensive test and is easy to perform.

Prevention and diagnosis of venous thromboembolism in critically ill patients: a Canadian survey

BACKGROUND

Venous thromboembolism (VTE) confers considerable morbidity and mortality in hospitalized patients, although few studies have focused on the critically ill population. The objective of this study was to understand current approaches to the prevention and diagnosis of deep venous thrombosis (DVT) and pulmonary embolism (PE) among patients in the intensive care unit (ICU).

DESIGN

Mailed self-administered survey of ICU Directors in Canadian university affiliated hospitals.

RESULTS

Of 29 ICU Directors approached, 29 (100%) participated, representing 44 ICUs and 681 ICU beds across Canada. VTE prophylaxis is primarily determined by individual ICU clinicians (20/29, 69.0%) or with a hematology consultation for challenging patients (9/29, 31.0%). Decisions are usually made on a case-by-case basis (18/29, 62.1%) rather than by preprinted orders (5/29, 17.2%), institutional policies (6/29, 20.7%) or formal practice guidelines (2/29, 6.9%). Unfractionated heparin is the predominant VTE prophylactic strategy (29/29, 100.0%) whereas low molecular weight heparin is used less often, primarily for trauma and orthopedic patients. Use of pneumatic compression devices and thromboembolic stockings is variable. Systematic screening for DVT with lower limb ultrasound once or twice weekly was reported by some ICU Directors (7/29, 24.1%) for specific populations. Ultrasound is the most common diagnostic test for DVT; the reference standard of venography is rarely used. Spiral computed tomography chest scans and ventilation-perfusion scans are used more often than pulmonary angiograms for the diagnosis of PE. ICU Directors recommend further studies in the critically ill population to determine the test properties and risk:benefit ratio of VTE investigations, and the most cost-effective methods of prophylaxis in medical-surgical ICU patients.

INTERPRETATION

Unfractionated subcutaneous heparin is the predominant VTE prophylaxis strategy for critically ill patients, although low molecular weight heparin is prescribed for trauma and orthopedic patients. DVT is most often diagnosed by lower limb ultrasound; however, several different tests are used to diagnose PE. Fundamental research in critically ill patients is needed to help make practice evidence-based.

Pleural fluid pH as a predictor of pleurodesis failure: analysis of primary data

STUDY OBJECTIVES

To determine the predictive accuracy of pH for identifying patients with malignant pleural effusions who will fail pleurodesis.

DESIGN

Analysis of published and unpublished individual patient-level data retrieved from a MEDLINE search and correspondence with primary investigators.

STUDY SELECTION

Studies that reported pleural fluid pH values and outcomes of pleurodesis for patients with malignant pleural effusions.

DATA COLLECTION AND ANALYSIS

Primary investigators supplied data for 433 patients. Receiver operating characteristic analysis and logistic regression estimated the predictive accuracy, decision thresholds, and value of pleural fluid pH compared with other clinical factors. The primary investigations were graded for study design.

RESULTS

Pleural fluid pH was the only independent predictor of pleurodesis failure (odds ratio, 4.46; 95% confidence interval [CI], 2.69 to 7.45; p < 0.0001) and had an area under the receiver operating characteristic curve (decision threshold, < or = 7.28) of 0.671 (95% CI, 0.624 to 0.715). The pH model fit the data well (p = 0.48) with the probability of pleurodesis failure increasing as pH decreased; specificity and negative predictive values for pleurodesis failure exceeded 90% and 80%, respectively, with a positive predictive value of 45.7% at pH values < or = 7.15. The primary studies had several important design limitations.

CONCLUSIONS

Using patient-level data, this study showed that pleural fluid pH has only modest predictive value for predicting symptomatic failure and should be used with caution, if at all, in selecting patients for pleurodesis. The limitations of the primary studies and low predictive accuracy should be considered when using pleural fluid pH for patient care.