Dr Rupert Jones gives advice on the tricky issue of diagnosing COPD and its differential diagnosis with asthma
COPD diagnosis is mired in controversy. Recent research has revealed that substantial numbers of patients with COPD are being misdiagnosed with asthma, and patients with asthma are ending up on COPD
But some patients have both conditions and so both need to be diagnosed correctly.
Defining and diagnosing COPD depends on spirometry.
Spirometry is easy to get wrong. Like all technical procedures, those performing spirometry should be competent, with adequate training, knowledge, experience and support.
In reality, surveys of primary care show a worrying picture of spirometry being performed by untrained staff in 75 per cent of practices, with more than half not knowing how to calibrate the spirometer.
Abnormal results are easy to misinterpret and practice nurses often have responsibility but little support1.
Hand-held spirometers are fine for use in primary care, but as they provide less information they are best reserved for screening or monitoring.
For making a diagnosis it is best to
use a spirometer which produces a graph.
Is it obstruction or restriction?
In obstruction, the air is blown out of the lungs more slowly the amount expired in one second is reduced, but ultimately a good volume is expired. The FEV1 is reduced (<80 per="" cent="" expected),="" but="" so="" too="" is="" the="" ratio="" of="" fev1:="" fvc="">80><70 per="" cent).="">70>
In restriction, the total amount breathed out is reduced, the FEV1 is reduced but as the speed of expiration is normal the ratio of FEV1:FVC is normal. Causes of restriction include chest wall problems (such as ankylosing spondylitis), pleural restriction (for example, pleural fibrosis, plaque or mesothel- ioma), and restriction of movement of the lung tissue (such as pulmonary fibrosis).
Is it asthma or COPD?
All obstruction is not COPD. Asthma can be difficult to separate from COPD and other diseases such as bronchiectasis even cancer of the bronchus can cause obstruction.
To establish whether it's asthma or COPD, a good history is the key did symptoms start in childhood, do the symptoms fluctuate day to day, do reliever inhalers work quickly and abolish symptoms?
If so, asthma is favoured. A gradual onset without major fluctuations, apart from when they have a chest infection, in a patient who is a heavy smoker, favours COPD.
Should you do reversibility testing?
Reversibility is not always necessary according to NICE and I would concur: in a recent study in Plymouth reversibility seldom changed a clinical diagnosis. But reversibility testing is recommended by the GOLD guidelines at diagnosis for every patient failure to do this can lead to an overestimation of COPD by 25 per cent2.
It seems there is a place for reversibility testing in many patients, but it can be omitted if the diagnosis is clinically straightforward. To meet the QOF requirements of reversibility testing for diagnosis, informal reversibility testing may be accepted by some PCTs ie, not to do formal reversibility testing, but give the patient a bronchodilator inhaler and at their next review see whether their spirometry has improved after having used it.
How does reversibility testing work?
Given a picture of obstruction on spirometry, if after bronchodilators spirometry reverses to normal it is not COPD. If it does not change it is irreversible obstruction, probably due to COPD.
It is the ones in between that cause the problems. The solutions are:
· reappraise the clinical picture
· if reversibility is more than 200ml or 15 per cent, asthma is likely
· if more than 400ml then they should be treated as asthma
· some patients can have both asthma and COPD, some have asthma only but
become less reversible with time these should both be treated with
inhaled steroids as per asthma, but
also may benefit from COPD treatments such as tiotropium or pulmonary
rehabilitation; only about 15 per cent have both diagnoses and should be Read coded as such.
Apart from spirometry, it is important for all newly-diagnosed patients to have a chest
X-ray and a full blood count. Also consider:
· alpha-1-antitrypsin level in those with early or rapidly progressive disease
· CT scan where diagnosis is in doubt
· in more severe disease an ECG can help
diagnose cor pulmonale or co-existing
ischaemic heart disease; also consider an echocardiogram
· pulse oximetry is useful for detecting
hypoxia and is indicated if FEV1 is less than 30 per cent expected, or cor pulmonale, polycythaemia or cyanosis are present.
Rupert Jones is a clinical research fellow at the Peninsula Medical School (primary care) in Plymouth where he leads the respiratory research unit; he is a GPSI in Plymouth PCT and chairs the COPD Pathways group
Competing interests Rupert Jones has received educational, research or travel grants from AZ, GSK, Boehringer Ingelheim/Pfizer, Altana Pharma and Ivax he is also the medical director of Patient Centred Software Ltd
The Plymouth experience
· In Plymouth, we have developed a strategy for managing COPD which incorporates a comprehensive assessment as well as management advice. A nurse trained in spirometry visited practices to look at COPD registers, and patients were invited to attend a clinic.
A computer software package designed for the project collates data, calculates and interprets questionnaires and issues reports on disease status and how it should be managed, for both GP and patient.
· More than 500 patients have been seen, and it is clear that about
25 per cent of patients on registers do not have COPD some have asthma and some other restrictive conditions. This overdiagnosis is occurring even after coding errors have been sorted.
· Equally, good studies indicate the prevalence of COPD in adults is about 9 per cent, and the prevalence in Plymouth on QOF data is about 1.5 per cent bearing in mind that 25 per cent may be misdiagnosed, it is clear that there is real underdiagnosis too.
Case studies: COPD, asthma or both?
Patient X (female, age 59)
Q. A cleaner with lifelong asthma, smokes 15 cigarettes/day, 10 pack years of smoking, now daily breathlessness and symptoms only partly relieved by salbutamol. FEV1 is 1 litre (41 per cent expected), FVC 2.1 litres (75 per cent expected), ratio 48 per cent. With reversibility testing FEV1 rises to 1.1 litre. She has little reversibility does this mean she has COPD?
A. No, not necessarily, we already know she has asthma the question here is does she have:
· poorly controlled asthma, or
· asthma that has become gradually less responsive to treatment, or
· does she have COPD and asthma?
Probably the only way to resolve this is with a course of prednisolone at 30mg/day for seven-14 days with daily peak flow chart. Whatever the result of reversibility testing, this sort of patient with long-term asthma should always be treated for her asthma, eg with inhaled steroids. Furthermore, reversibility testing is unreliable in current smokers as they may show little reversibility, but this changes after they stop smoking.
Patient Y (male, age 60)
Q. Ex-very heavy smoker and drinker 80 pack years and no atopic background. He appears fit, but FEV1 0.95 litre (27 per cent expected), FVC 2.6 litres (59 per cent expected), ratio 36 per cent. What is the most likely diagnosis?
A. The clinical diagnosis is clearly severe COPD. Reversibility testing is not indicated according to NICE. However, he was given six puffs of salbutamol via a volumatic and his FEV1 changed to 1.1 litre (31 per cent expected). So what? Well the answer is that this result does change things. Although he shows little reversibility (<200ml), he="" is="" now="" classified="" by="" nice="" as="" having="" moderate="" obstruction.="" (it="" is="" worth="" noting="" that="" the="" severity="" grading="" based="" on="" fev1="" percentage="" of="" expected="" for="" the="" gold="" guidelines="" is="" based="" on="" post-bronchodilator="" results="" to="" avoid="" this="" issue.)="">200ml),>
Furthermore, according to NICE, if FEV1 is <30 per="" cent="" he="" should="" have="" pulse="" oximetry="" and="" possibly="" formal="" oxygen="" assessment="" ="" after="" reversibility="" testing="" this="" is="" no="" longer="">30>
Patient Z (female, age 46)
Q. A smoker with 20 pack years presents with cough, wheeze and sputum. No atopic background. She has had three courses of antibiotics in the last four months and wants something stronger this time to clear the infection. Her chest is wheezy. FEV1 1.7 litres (68 per cent expected), FVC 2.4 (expected 83 per cent), ratio 71 per cent. After reversibility testing, her FEV1 rises to 2.2 litres (83 per cent expected). What is her diagnosis?
A. She now has normal FEV1 percentage expected and this excludes COPD. She has asthma.