Practice dilemma: How can I diagnose asthma without access to tests?

Respiratory nurse specialist Marieke Strange advises on how to cope with delays for spirometry and other tests when assessing patients for asthma

The dilemma: We have virtually no access to spirometry or FeNO testing locally, so every time I see a patient with suspected asthma I am faced with delays trying to perform the recommended tests. What’s the best approach for diagnosis in these situations? 

It is a difficult place to be in when diagnostic tests aren’t available for a ‘quick fix’, but we have to remember these tests will not always give you a reliable answer.

A thorough history is key

Firstly, the history is paramount: what the triggers are, how long symptoms have been going on, what started them, family history, past medical history and any aggravating and alleviating factors. What is all this information telling you?

Related Article: Quick quiz: Diagnosis of COPD

If the symptoms are not absolutely typical of asthma, explore other possibilities. This depends on the symptoms (for example, cough, shortness of breath) but any can have other causes, such as an underlying cardiac abnormality, anaemia or even cancer, so a chest X-ray and basic bloods are a sensible starting point.

Remember FeNO and spirometry have their limitations

If you feel asthma is likely, tests are indicated. Yes, spirometry and FeNO are helpful, but the recently updated NICE guidance now only recommends one objective test to confirm a diagnosis in patients with suggestive symptoms. In addition, for adults, NICE now recommends a blood test to check the eosinophil count can be done as an alternative to FeNO.

For both adults and children, a peak expiratory flow (PEF) diary can also be helpful, and NICE now explicitly recommends this if there would be a delay in arranging other tests.

Remember the purpose of these tests is to confirm your suspicion of an asthma diagnosis based on the history and symptoms.

Spirometry can be helpful although is mainly done to confirm that any airway obstruction is not due to something else, such as COPD. Also it is always important to do reversibility testing, as even where spirometry is normal, there may still be a significant bronchodilator response (ie, leading to a significant increase in FEV1). This is because a patient’s airway tests can ‘underperform’ on their personal best, while still being within the normal on the average scale by which spirometry measures.

FeNO levels can be raised for reasons other than asthma, such as allergic rhinitis.

Remember also that patients sometimes warrant an asthma diagnosis ‘despite’ a normal spirometry or FeNO result. Because asthma is often trigger related, there is chance of tests being normal, even in the presence of asthma (spirometry more so than FeNO).

Related Article: Reliability of routine asthma test varies with time of day and season

Obtaining a good PEF diary is essential

If using a PEF diary, it is important that the patient understands why these tests are performed, to encourage them to take the readings consistently – the more readings they can provide, the easier the interpretation. The patient should perform peak flow readings for 2 weeks (morning and evening as a minimum) and bring the diary to a face-to-face appointment with you (or a colleague who can interpret the results).

This Primary Care Respiratory Society guidance explains how to interpret peak flow readings.

Essentially, patients should be encouraged to take at least two readings a day, one in the morning and one in the evening, ideally for 14 days.

The average percent variability is then calculated by working out the % daily variability ([Highest–Lowest PEF/Mean PEF] x 100) for each day and taking the average over 14 days (Total % daily variability/14).

Overall, variability of 10-20% is significant and a reading nearer 20% is supportive of a diagnosis of asthma.

Related Article: How asthma management is changing – what nurses need to know 

Keep an open mind and monitor treatment response

It is very important in asthma care to monitor patients and have a follow up appointment in place, once started on asthma treatment. If symptoms don’t respond to asthma treatment – inhaled corticosteroids with a good inhaler technique, for at least 6 weeks (ideally 8 weeks) – then the likelihood of asthma is significantly reduced. This should be clearly recorded in the notes and inhalers should ideally be stopped. At this point you should refer to secondary care for further testing.

Marieke Strange is a primary care respiratory specialist nurse based in Bristol