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Diagnosis of asthma
University of Southampton
E-mail: j.lynch{at}soton.ac.uk
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Abstract |
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 TOP Abstract Asthma and the GP...Diagnosis of a severe...References |
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Asthma is a condition of paroxysmal, reversible airways obstruction. It is due to a chronic underlying inflammatory process and has characteristic features of reversible airway narrowing and airway hyper-responsiveness to a wide range of stimuli.
There are six core competences for GPs from the RCGP curriculum (www.rcgp-curriculum.org.uk):
The curriculum states that specific problem-solving skills are concerned with the ability:
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Severity
Asthma varies from mild intermittent symptoms to a mortal illness. Over 1100 people died from asthma in the UK in 2005, including 20 children aged under 14. It has been estimated that up to 90% of these deaths could be avoided. Appropriate diagnosis followed by adequate treatment is vital to achieve this.
Epidemiology
Estimates of prevalence vary widely depending on the criteria used. European Respiratory Health Survey figures suggest that 25% adults aged 20–44 years suffer from wheeze, 15% suffer from wheeze with breathlessness and 7% have doctor-diagnosed asthma. There is marked geographical variation. Asthma can be divided into ‘intrinsic asthma’ with no triggers which typically starts in middle age while ‘extrinsic asthma’ has identifiable triggers and tends to affect children and young people. Occupational asthma, caused by a workplace allergen, accounts for 1–2% of adult asthma.
Diagnosis in adults
Diagnosis of asthma is important both as a learning requirement and to comply with the GMS contract (Box 1). However, the diagnosis of asthma is most important as a skill that is needed on a daily basis in general practice. Patients still die of asthma and it therefore important that doctors can appropriately diagnose (and treat) a patient presenting with symptoms of asthma.
Asthma is a clinical diagnosis but it is not always clear-cut as sufferers have a variety of symptoms—none of which are specific for asthma. There are tests which can aid diagnosis in adults or older children but these are also non-specific. Therefore diagnosis consists of history, examination and tests followed by an evaluation of the probability of asthma. The new British guidelines on asthma suggests classifying people into high, intermediate and low probability of asthma according to initial investigations with a plan of action for each group (Fig. 1).
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| Box 1 The GMS Contract and Asthma diagnosis. Asthma 1: The practice can produce a register of patients with asthma, excluding patients who have been prescribed no asthma-related drugs in the last 12 months. Asthma 2: The percentage of patients aged eight or over diagnosed as having asthma from 1 April 2003 where the diagnosis has been confirmed by spirometry or peak flow measurement.
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History
An accurate history may be the most important part of diagnosis and a detailed plan to a general respiratory history is shown in Table 1. A diagnosis is made when there is characteristic pattern of symptoms and the absence of an alternative explanation. The typical symptoms associated with asthma are wheeze, breathlessness, chest tightness and cough. The presence of more than one of these increases the probability of asthma particularly if the symptoms are worse at night or early morning, occur in response to a trigger such as exercise, allergen exposure or cold air or after taking drugs such as aspirin or β-blockers. Other significant features in the history which increase the probability of asthma are a personal history of atopy or a family history of asthma or atopy. In adults, if asthma is likely then the history should also explore the potential cause, particularly occupational.
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Asthma is less likely if there is a significant smoking history [consider chronic obstructive pulmonary disease (COPD)], a chronic productive cough only, prominent dizziness, light-headedness or peripheral tingling (consider hyperventilation) or a history of cardiac disease.
Occupational asthma
More than 200 industrial materials are known to cause occupational asthma. Suspect occupational asthma if the patient has symptoms which improve on days away from work or on holiday. These patients should always be referred to a respiratory physician.
Examination
A guide to a full respiratory examination is shown in Table 2. Often there will be no signs if the patient is well. Symptomatic patients may have a widespread wheeze which is bilateral, diffuse, polyphonic and more pronounced on expiration compared to inspiration—document in notes if heard. However, it is important to note that severe episode of asthma can result in a silent chest due to the lack of airflow and these patients need rapid treatment. Some patients with chronic asthma will have a characteristically shaped ‘Barrel chest’, a sign of hyperinflation.
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Tests
Objective tests should be used in adults to confirm diagnosis of asthma before long-term treatment is started. In general practice, this involves peak expiratory flow rate (PEFR) measurement and spirometry. A normal test result when the patient is not symptomatic does not exclude a diagnosis of asthma but repeated normal results when the patient is symptomatic should lead to a re-evaluation of the diagnosis.
Peak flow
This is a simple and cheap test which is a more effective measure of disease or treatment progress than of diagnosis. However, it can be used when spirometry is not available. PEFR should be interpreted by what is normal for that person; charts are available to suggest normal values according to height and age but readings up to 100 l/min lower than predicted in men and 85 l/min in women are within normal limits. Table 4 shows predicted values in a Caucasian population. PEFR characteristically varies over time and most asthmatics show diurnal variation, with an early morning dip in PEFR measurements. Peak flow meters are available on NHS prescription. Since 2004, EN 13826 /EU standard peak flow meters are supplied. Peak flow charts are available from NHS supplies (Form FP1010) and drug companies.
- Interpretation of peak flow in asthma
- 50–80% predicted or best = moderate exacerbation
- 33–50% predicted or best = severe exacerbation
- Less than 33% predicted or best = life-threatening asthma
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| Measuring PEFR Ask the patient to stand up (if possible) and hold the peak flow meter horizontally. Check the indicator is at zero and the track clear. Ask the patient to take a deep breath and blow out forcefully into the peak flow meter ensuring lips are sealed firmly around the mouthpiece. Read the PEFR off the meter. The best of three attempts is recorded. Consider using a low range meter if predicted or best PEFR is less than 250 l/minute.
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Spirometry
This can be used to help diagnose asthma and exclude other forms of lung disease. It can also be used instead of PEFR to demonstrate variability (at least 15% variation in FEV1 with a minimum change in FEV1 
200 l/minute suggests asthma). It measures the volume of air the patient is able to expel from the lungs after a maximal inspiration and three values are produced:
- FEV1: volume of air the patient is able to exhale in the first second of forced expiration.
- FVC: total volume of air the patient can forcibly exhale in one breath.
- FEV1/FVC: ratio of FEV1 to FVC expressed as a percentage.
If patients have normal or near-normal values when symptomatic, then a respiratory cause of the symptoms is unlikely.
Measuring PEFR
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Interpretation of spirometry results
Some spirometers will give a flow–volume curve which may show an obstructive picture as shown in Fig. 2. Otherwise a reduced ratio of FEV1 and FVC suggests an obstructive picture (Table 6). Patients with COPD will have a constant obstructive result while patients with asthma would be expected to return to a normal picture when asymptomatic.
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Chest X-ray
This needs to be considered for any patient with new, atypical or additional symptoms.
Other tests
These may be useful in selected patients and include skin prick tests: consider for occupational asthma and asthma which is more difficult to control; blood eosinophil count and serum IgE.
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Diagnosis of a severe asthma attack in adults |
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TOPAbstractAsthma and the GP...Diagnosis of a severe...References |
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Symptoms/signs of a severe asthma attack:
- Unable to talk in sentences without stopping for breath
- Tachypnoea (respiratory rate Greater than 25 breaths/minute)
- Intercostal recession
- Tachycardia (heart rate Greater than 100 bpm)
- PEFR Less than half predicted or best
Life-threatening signs:
- Central cyanosis
- Silent chest (inaudible wheeze)
- PEFR Less than a third predicted or best
- Hypotension
- Bradycardia
- Confusion or exhaustion
Differential diagnosis in adults
There are respiratory and non-respiratory causes of respiratory symptoms which need to be considered when making a diagnosis. Respiratory causes can be due to localized obstruction of the airways such as cancer (lung, trachea and larynx), foreign body or post-tracheotomy stenosis. While generalized obstruction of the airways includes COPD, cardiac disease, pulmonary embolism, interstitial lung disease, aspiration, bronchiectasis and cystic fibrosis.
If spirometry does not show an obstructed picture consider chronic cough syndrome, hyperventilation, vocal cord dysfunction, rhinitis, gastro-intestinal reflux or pulmonary fibrosis. Also consider respiratory symptoms of non-respiratory disease which can include cardiovascular disease, anaemia, depression, diabetes, thyroid disease, spinal dysfunction, anxiety/panic attacks and neuromuscular disease
Referral to secondary care
A secondary care referral should be considered if there is:
- Diagnostic confusion e.g. unexpected clinical findings (e.g. clubbing, cyanosis); spirometry or PEFR does not fit the clinical picture
- Suspected occupational asthma
- Persistent shortness of breath
- Unexplained restrictive spirometry
- Unilateral or fixed wheeze
- Chest pain
- Weight loss or other prominent systemic features such as myalgia or fever.
- Persistent cough with sputum production
- Non-resolving pneumonia
- Marked eosinophilia (Greater than1 x 109/l)
- Poor response to treatment
An urgent referral should be made to a chest physician
- Persistent haemoptysis in smoker or ex-smoker over 40 years of age
- Signs of superior vena cava obstruction (swelling of the face and/or neck with fixed elevation of jugular venous pressure (emergency referral)
- Stridor in adults
- Life-threatening symptoms
- Suspicion of cancer
Diagnosis of asthma in children
Childhood asthma affects approximately 5% of children in the UK and the prevalence is increasing. Virus associated wheeze affects up to 20% of children at some point. Peak age of onset of childhood asthma is 5 years. Despite increased detection and better treatment of asthma in recent years in the UK children still die every year from the disease. As for adults, diagnosis is clinical and based on probability of diagnosis based on the child's history and signs (Fig. 3).
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Risk factors
A variety of social, genetic and environmental factors increase the risk of children developing asthma. A family history of atopy particularly from the mother and/or siblings increases the risk as does a personal history of atopy. This also increases the risk of persistence in symptoms; most children presenting under the age of 2 years are free of symptoms by the ages of 6–11 unless they have a personal history of atopy. Pre-puberty more boys than girls are affected (3:2) but boys are likely to ‘grow out’ of their symptoms and after puberty there is a greater prevalence in girls. Other factors increasing the risk are prematurity, bronchiolitis in infancy and parental smoking particularly in the mother.
History
This should follow the questions used for adults (Table 1) but adapting as necessary for the age of the child. The most common presentations are episodes with one or more symptoms of cough, wheeze, breathlessness and chest tightness. These episodes are recurrent and worse at night or in the morning, between episodes the child is typically symptom-free.
Symptoms are often exacerbated by upper respiratory tract infections, exercise and exposure to allergens such as tobacco smoke, dust and animals. A personal history of atopic disorder or a family history of atopy or asthma increases the probability of diagnosis.
There is reduced probability of the child having asthma if symptoms only occur with colds or the child only has symptoms of cough particularly if it is a moist cough. In addition, if the examination is repeatedly normal when the child is symptomatic, there is no response to a trial of asthma therapy or there are other symptoms, then an alternative diagnosis should be considered. However, a trial of therapy may be the only way to make a diagnosis and therapy should not be withheld if asthma is a possibility.
Examination
This will often be normal and should be normal between episodes, the normal values for respiratory rate and pulse in children are shown in Table 7. When the child is symptomatic, there may be an audible wheeze but do not discount the history if this is not heard. Severe asthma can lead to a ‘pigeon chest’.
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Testing
Young children will not be able to perform airways testing and British guidelines state that further testing adds very little to the diagnosis in children. Those with a high probability of asthma should move straight on to a trial of treatment. For other children, it may be worth trying PEFR or spirometry but beware that reproducibility will not be good in younger children and impossible in those pre-school. Height is the only determinant of PEFR in children and predicted values are shown in Table 8. With increasing age, the pattern of adult values takes over.
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Diagnosis of severe asthma in children
Symptoms and signs of a severe attack in children over the age of 2 years
- Unable to complete sentences in one breath or too breathless to talk/feed
- Tachycardia
- pulse greater than 120 beats per minute if over 5 years of age or greater than 130 beats per minute if aged 2–5 years.
- pulse greater than 120 beats per minute if over 5 years of age or greater than 130 beats per minute if aged 2–5 years.
- Tachypnoea
- respiratory rate of over 30 breaths/minute if over 5 years of age or greater than 50 breaths/minute if aged 2–5 years
- respiratory rate of over 30 breaths/minute if over 5 years of age or greater than 50 breaths/minute if aged 2–5 years
Life threatening signs in children over the age of 2 years
- Central cyanosis
- Silent chest (inaudible wheeze)
- Poor respiratory effort
- Confusion
- Exhaustion
- Hypotension
- Coma
Symptoms and signs of significant attack in a child under the age of 2 years
- Oxygen saturation of Less than 92%
- Marked respiratory distress
- Cyanosis
- Too breathless to feed
Life threatening features
- Episodes of apnoea
- Poor respiratory effort
- Bradycardia
Differential diagnosis
This will depend on the age of the child and the presenting symptoms (Table 9). For very young children or those who have had symptoms from a young age, developmental or congenital causes should be considered. Older children are more likely to have infective causes.
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Key points
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References |
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TOPAbstractAsthma and the GP...Diagnosis of a severe...References |
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Asthma UK. website www.asthma.org.uk.
British Thoracic Society. British Guideline on the Management of Asthma. Thorax (2008) 63(suppl_4). Accessed via www.thorax.bmj.com/cgi/issue_pdf/cover_pdf/63/Suppl_4.pdf[date last accessed 14.08.2008].
Lynch J, Simon C. Oxford General Practice Library: Respiratory Problems (2007) Oxford: Oxford University Press.
Mortality Statistics series DH2 no. 32. Accessed via www.statistics.gov.uk/statbase/Product.asp?vlnk=618 [date last accessed 14.08.2008].
Peak Flow. website www.peakflow.com.
RCGP GP Curriculum statement 15.8: Respiratory problems. www.rcgp-curriculum.org.uk/PDF/curr_15_8_Respiratory_problems.pdf [date last accessed 11.11.2008].
Warrell D, Cox T, Firth J, eds. Oxford Textbook of Medicine, (4th edition - 2005). Oxford: Oxford University Press. ISBN 978-0-19-85978-7.
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