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Diagnosing obstructive airway disease

Study
Results
Comment
Bandolier wishes it had the EBM equivalent of a Nobel prize to hand out. The prize for the most important contribution to the evidence-base of diagnosis would certainly go to the CARE group (Bandolier 66) investigating the diagnosis of obstructive airway disease [1]. The evidence base in diagnosis and diagnostics is so awful it beggars belief, so when an innovative method using clinicians around the world collaborating through the Internet comes up with the right stuff it is as welcome as a cold glass of water in the desert.

The present study derived from a systematic review of diagnostic criteria for obstructive airways disease (OAD) [2]. It sought physical signs for differentiating between patients with OAD and those with normal pulmonary function. There were many criteria mentioned, but no one sign was found in more than a third of studies. For each of the four most commonly used physical signs the range of diagnostic accuracy from the literature was huge. Positive likelihood ratios spanned the range from about 1 to over 10: from useless to highly predictive.

They also examined the quantity and quality of evidence from systematic reviews for a variety of signs for different conditions. There were few high-quality studies, and those there were were small. The bottom line was that we had little or no objective proof of the quality of diagnostic accuracy of the clinical examination for OAD.

Study

Investigators from around the world were recruited via the CARE Internet site (www.carestudy.com) and the evidence-based email discussion group. Participating groups had at least one physician and one spirometrist and enrolled at least four consecutive patients from each of three categories:

  1. Patients known to have chronic OAD. This was defined as prior pulmonary function test results less than fifth percentile, patient self report of chronic OAD, bronchitis or emphysema, or use of bronchodilators or steroids.
  2. Patients suspected of having OAD who did not fulfil criteria of known OAD but were referred for suspected OAD or the physician thought that OAD was a diagnostic possibility.
  3. Patients neither known nor suspected of having OAD.

There were various exclusions, like reversible airway obstruction such as asthma, those with terminal illnesses, and concomitant serious medical conditions.

All the patients underwent clinical examination and independent blinded spirometry. Diagnostic criteria chosen for examination based on the earlier systematic review and consensus were:


Each patient underwent a standard protocol for spirometry within 30 minutes of the clinical examination. The gold standard definition of OAD was FEV1 and FEV1-FVC ratio less than the fifth percentile.

Results


Twenty-five investigator groups in 13 countries recruited 322 patients in one month. After excluding some with asthma the final sample size was 309. Likelihood ratios were calculated for all patients, and for those without known chronic OAD. They key indicators were self-reported history of chronic OAD, smoked more than 40 pack years, age 45 or more, maximum laryngeal height 4 cm or less.

For all patients, if all four factors were present the likelihood ratio was a massive 221 (Table). Given a population in which the prior likelihood of OAD was 10%, the post-test probability would be 96%. This would essentially rule in OAD. When all four factors were absent, the post-test probability would be about 1%, essentially ruling out the diagnosis. Where there was no prior history, the three remaining factors achieved much the same result.

Table: Likelihood ratios for the four important diagnostic criteriafor chronic obstructive airways disease

 
Likelihood ratios
 
All 309 patients
233 patients without known chronic OAD
Diagnostic element
Factor present
Factor absent
Factor present
Factor absent
Self-reported history of OAD
7.3
0.5
 
 
Smoked more than 40 pack-years
8.3
0.8
11.6
0.9
45 years or more
1.3
0.4
1.4
0.5
Maximum laryngeal height 4 cm or less
2.8
0.8
3.6
0.7
All factors
221
0.13
59
0.32

Comment


This study triples the number of patients and increases the number of clinicians ten fold over the previous rigorous examination of diagnosis of chronic OAD. It demonstrates that exemplary information about diagnosis can be achieved quickly by use of the Internet. Investigators were involved from Argentina, Australia, Canada, Chile, Colombia, England, Italy, New Zealand, Romania, Spain, Saudi Arabia, United Arab Emirates, and the United States. It is a model for diagnostic testing research, and shows that a number of different issues can quickly be accomplished with a bit of thought. Just imagine what could be done if real resource was put into sorting out diagnostic testing.

This tells us which clinical criteria are important. If spirometry is available, of course it should be used. Where it isn't the data provide useful diagnostic support for the clinician. More please.

Reference:

  1. SE Straus, FA McAlister, DL Sackett, JJ Deeks for the CARE-COAD1 Group. The accuracy of patient history, wheezing, and laryngeal measurements in diagnosing obstructive airway disease. JAMA 2000 283: 1853-1857.
  2. FA McAlister, SE Straus, DL Sackett. Why we need large, simple studies of the clinical examination: the problem and a proposed solution. Lancet 1999 354: 1721-24.
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