Differentiating Asthma from COPD

Whilst asthma and COPD are different diseases they cause similar symptoms, which can present a challenge in identifying which of the two diseases a patient is suffering from. A patient survey by the British Lung Foundation (BLF) showed that nearly 39% of COPD patients had been told they have asthma.

There are, however, some important distinctions between asthma and COPD. COPD causes chronic symptoms and narrowed airways which do not respond to treatment to open them up. In the case of asthma the constriction of the airways through infl ammation tends to come and go and treatment to reduce infl ammation and to open up the airways usually works well.

COPD is more likely than asthma to cause a chronic cough with phlegm and is rare before the age of 35 whilst asthma is common in under-35s. Disturbed sleep caused by breathlessness and wheeze is more likely in cases of asthma, as is a history of allergies, eczema and hayfever. Differentiating between COPD and asthma requires a history of both symptoms and spirometry. The spirometry history should include post bronchodilator measurements, the degree of reversibility and, ideally, home monitoring which gives a history of diurnal variation.


What are the definitions?

Airflow Obstruction: Both asthma and COPD are characterised by airflow obstruction. Airflow obstruction is defined as a reduced FEV1 and a reduced FEV1/FVC ratio, such that FEV1 is less than 80% of that predicted, and FEV1/FVC is less than 0.7.

Asthma: Asthma is a chronic inflammatory disorder of the airways in which many cells and cellular elements play a role. The chronic inflammation is associated with airway hyperresponsiveness that leads to recurrent episodes of wheezing, breathlessness, chest tightness and coughing, particularly at night or in the early morning. These episodes are usually associated with widespread, but variable, airflow obstruction within the lung that is often reversible either spontaneously or with treatment1.

COPD: COPD is a chronic, slowly progressive disorder characterised by airflow obstruction (reduced FEV1 and FEV1/VC ratio) that does not change markedly over several months. The airflow obstruction is not fully reversible2.


Clues to the Difference Between COPD and Asthma
History COPD Asthma
Age Over 35 Any age
Dyspnoea varies A little A lot
Onset of dyspnoea Gradually Sudden bouts
Dyspnoea at rest Uncommon Common
Smoking history > 20 pack years Variable
Wheezing as a child Uncommon Common
Productive cough For many years Associated attacks
Morning coughing fits Common Uncommon
Nocturnal cough wakes Uncommon Common
Family history Uncommon Usually
Atopy Unusual Often
Steroid responsiveness Weak Strong
Anticholinergic response Usually good Beta-agonists better
Beta-agonist response Anticholinergics better Very good

Note: COPD is more likely to affect older people. The vast majority of sufferers are aged 70 to 85. COPD patients also tend to have frequent acute respiratory infections which can also accelerate the decline of FEV1.


Confirm or Preclude COPD or Asthma with Spirometry
Spirometry COPD Asthma
VC Reduced Nearly normal
FEV1 Reduced Reduced in attack
FVC (or FEV6) Reduced Nearly normal
FEV1 Ratio (of VC/FVC/FEV6) Reduced anytime Reduced in attack
FEV1 as % of predicted (or SDS*) <LLN Reduced in attack
Bronchodilator reversibility A little Marked if in attack
Serial spirometry Progressive deterioration Constant or erratic
Home monitoring Use for alerts Use for variability
Peak Flow measurement Not useful As above
Peak Inspiratory Flow measurement Not useful Not useful

* SDS = Standard Deviation Score. In comparing your test subject to a ‘normal population’ using SDS or LLN (Lower Limit of Normality) is preferred to percent of predicted because the latter gives false negatives for younger people and false positives for older people.


Serial Spirometry

The most important objective measurement of all in lung disease management is serial spirometry. Taking a single lung function measurement may or may not yield useful information. But comparing that spirometry test data, particularly the FEV1, with data from the previous few years yields invaluable, yet simple, information.

Serial_Spirometry As a normal growing child it is fairly obvious that the lung function values will rise according to the individual’s growth centiles. After achieving adulthood, and a period of a few years without change in values, every normal person will have a gradual decline lung function. In disease this pattern may radically change.

In older people, the rate of decline of a COPD sufferer can be two or three times the FEV1 decline in normal people. Medical intervention can bring this back to a normal rate of decline, but not back to the level of a normal person. For this reason early detection is crucial. It is very possible to detect this accelerated rate of decline even when the patient is in 'normal range'. An accelerated rate of decline detected by serial spirometry is definitely abnormal, no matter if the patient still has 'good' lung function values3.

A serial spirometry plot like the one pictured here is typical of uncontrolled COPD, such as a sufferer who keeps smoking4.

Serial spirometry is impossible without spirometry quality control. Without consistently accurate measurements, the serial data will be useless, or worse, misleading. Although serial spirometry can help identify device or procedural problems, this is shutting the door after the horse has bolted. The real answer is training and quality control.

Spirometry Quality Control

Spirometer accuracy: An accuracy check is a is a two minute check that you do just before starting your asthma or COPD clinic and is as simple as setting the device to 'accuracy check' mode (for ATPS measurement) then pumping the 3-L syringe. If all is well the device will measure 3L ±3%. It is important not to confuse ‘calibration’ with an accuracy check. Calibration is an annual certifi cation of traceability to international measurement standards which may or may not involve adjustment prior to certifi cation.

Test acceptability: When testing, each forced expiratory blow comprising part of the session data must be acceptable. This means that there is a good start of test, no artefacts such as coughing and a good end expiratory plateau and a test duration of over 6-s (3-s in children under 10 years). Premature test termination is the most common error in spirometry.

Number of blows: The spirometry guidelines require that a test session comprise of a minimum of 3 satisfactory blows to ensure that the forced expiratory volumes are 'the best'. Of course usually more blows are required as there are usually some unsatisfactory blows, especially if a slow VC test does not precede the FVC, or the operator fails to use a disposable noseclip.

Repeatability: The satisfactory blows must be repeatable within 5% on both FEV1 and FVC. In practice this means the best two blows.

Training & Over-reading: None of the above can be achieved without proper training. The use of over-reading for ECG interpretation is widely used, but over-reading spirometry reports is relatively new in primary care. New technology is making automation of over-reading possible.


Home Monitoring

Home monitoring of lung disease is important to alert the patient of exacerbations and for providing invaluable objective data to the practitioner. Additionally, the patient may be given an 'action plan' for helping them to manage their condition or to know when to seek medical intervention. According to BTS/SIGN5 "Written personalised action plans as part of selfmanagement education have been shown to improve health outcomes for people with asthma" and "Prior to discharge, in-patients should receive individualised asthma action plans, given by clinicians with appropriate training in asthma management."

The use of mechanical peak flow meters may not be adequate for lung diseases other than asthma6. Today accurate and inexpensive home monitors are available which record FEV1 and even FEV6 as well as having the facility to set a personalised action plan for the patient. For PEF measurement in asthmatics, inexpensive electronic home monitors can also be used which avoids the need for paper records and misleading 'false reporting'.


References:

1. Global Strategy for Asthma Management and Prevention. Global Initiative for Asthma (GINA), 2011. Available from www.ginasthma.org

2. Global Initiative for Chronic Obstructive Pulmonary Disease: NHLBI/WHO workshop report. 2001 National Institutes of Health. Bethesda, MD: publication No. 2701 http://www.goldcopd.com

3. P. Vineis, Smoking and Impact on Health, Eur. Respir. Rev 2008: 17: 110, 182-186. World Asthma Day 2009 is on May 5th.

4. Anthonisen NR, Connett JE, Kiley JP, et al. Effects of smoking intervention and the use of an inhaled anticholinergic bronchodilator on the rate of decline of FEV1. The Lung Health Study. JAMA 1994; 272: 1497–1505.

5. British Thoracic Society, Scottish Intercollegiate Guidelines Network. British Guideline on the Management of Asthma. SIGN; 2010. http://www.sign.ac.uk

6 Chronic Obstructive Pulmonary Disease. National clinical guideline on management of chronic obstructive pulmonary disease in adults in primary and secondary care Thorax March 2004, Volume 59, Supplement 1.