Diagnosis of Asthma

Author: V. Dimov, M.D., Allergist/Immunologist and Assistant Professor at University of Chicago
Reviewer: S. Randhawa, M.D., Allergist/Immunologist and Assistant Professor at NSU

Asthma is the most common chronic respiratory disease, affecting up to 10% of adults and 30% of children (JACI, 2011). Approximately 9% of the U.S. population has asthma - 9% of adult asthmatics have aspirin-exacerbated respiratory disease (AERD) (http://goo.gl/FIeE9).

Asthma is a chronic inflammatory disorder of the airways which causes recurrent episodes of:

- wheezing
- shortness of breath
- chest tightness
- cough

Episodes are associated with variable airflow obstruction that is reversible.

Asthma diagnosis (click to enlarge the image).


Symptoms may consist of:

- wheezing
- shortness of breath
- chest tightness
- cough

Cough occurs in most patients with asthma and may be the only symptom in cough-variant asthma.

Link between asthma and allergic rhinitis

Most patients with asthma have rhinitis suggesting the concept of ‘one airway one disease’ or ‘united airways’. However, not all patients with rhinitis present with asthma.

The 1999 WHO workshop ‘Allergic Rhinitis and its Impact on Asthma’ recommended:

- patients with persistent allergic rhinitis should be evaluated for asthma by history, chest examination, and possibly assessment of airflow obstruction before and after bronchodilator

- history and examination of the upper respiratory tract for allergic rhinitis should be performed in patients with asthma

Allergic Rhinitis and its Impact on Asthma (ARIA): Achievements in 10 years and future needs. ARIA has reclassified AR as mild/moderate-severe and intermittent/persistent. This classification closely reflects patients' needs and underlines the close relationship between rhinitis and asthma. http://buff.ly/QL1eYI

Physical Examination

The most common sign of airways obstruction (and asthma) is wheezing. Patients with
severe obstruction may not be able move air fast enough to generate vibration and audible wheezing.

Pulmonary Function Tests (PFTs)

Pulmonary function tests (PFTs) are the most objective way to document the diagnosis of asthma.

A mnemonic to remember the different PFTs is SPIROMEtry:

Inhalation tests:
Reversibilty of
Obstruction with beta-agonist
Metacholine challenge
Exhaled NO

PFTs (click to enlarge the image).


The patient executes a forced expiratory maneuver by:
1. breathing normally several times
2. exhaling fully followed by a deep inhalation
3. forceful exhalation that should last at least 6 seconds

The phases of spirometry can be remembered by the mnemonic BEIF:

Breath normally x 6 times
Exhale fully
Inhalation (deep)
Forceful exhalation for 6 seconds

There should be no cough, glottic closure or air leak during the forceful exhalation for 6 seconds. The best effort of 3 is used. All efforts should have forced vital capacities (FVC) that are within 5% or 0.1L of each other. Individual volumes are called volumes whereas the combination of volumes is called a capacity.

Decreased in obstruction
Normal or increased in restriction

FEF 25-75
Decreased in obstruction
Normal or increased in restriction

FEF 25-75
Regular (normal) or
Raised in

1ow in both obstructive and restrictive disease

FEV1 is the most commonly used and best-standardized measurement in spirometry. FEV1 is effort-dependent, similary to PEFR.

FEV1 is used to confirm the diagnosis of asthma when airways obstruction
is present by:
- baseline spirometry
- inhalation of a short acting β-agonist
- repeat spirometry in 15-20 minutes to show reversibility of obstruction


Baseline spirometry

Repeat spirometry
Reversibilty of obstruction

An improvement in the FEV1 of 12% and 200 mL shows a significant reversibility and is highly specific for asthma

The criteria for reversible bronchoobstruction to diagnose asthma include improvement of 200 ml AND 12 % (not 200 ml OR 12%) after bronchodilation -- both have to be present. The change can be in either FEV1 or FVC.

The test is not very sensitive though. A 12% change in FEV1 is unlikely to be seen in:

- asthmatic patients with normal FEV1
- chronic asthma that has become irreversible because of airways remodeling

Peak Expiratory Flow Rate (PEFR)

PEFR is highly effort dependent, similarly to FEV1. PEFR is less reproducible than FEV1.

Patients should determine their personal best peak flow rather than relying on a chart of predicted peak flows based on height and age. PEFR normally vary about 5%, with the evening values higher than morning values. When asthma is uncontrolled, the normal diurnal variation in PEFR are exaggerated, and the values may vary 20-30%.

Methacholine challenge test

The methacholine challenge test mesaures bronchial hyperreactivity in response to a provoking agent (metacholine).

Bronchial challenges can be performed with:
- methacholine (a cholinergic agonist)
- histamine (used as a positive control in skin prick testing)
- antigen
- cold air (a surrogate for exercise-induced asthma)

95% of patients with asthma have a 20% reduction in FEV1 when given 5 breaths of 25 mg/mL of methacholine.

It is easier to remember the numbers: 5-25-20-5:

5 breaths
25 mg/mL metacholine
20% FEV1 reduction
5% of patients with asthma have a negative test, 95% react to the challenge

Metacholine challenge test has a 95% negative predictive value in excluding asthma. In other words, the utility of metacholine challenge test is to exclude asthma not to diagnose it.

Methacholine challenge test is generally safe.

Relative contraindications:
- FEV1 less than 70% of predicted
- patients taking beta-blockers, e.g. Atenolol
- Bradycardia (can be worsened by cholinergic agents)

Methacholine is more sensitive than mannitol for evaluation of bronchial hyperresponsiveness in children with asthma http://goo.gl/Dh0m

Methacholine is not as sensitive to diagnose asthma as previously thought, according to a 2011 review published on Medscape (http://goo.gl/ajn0S).

Sputum findings in asthma

- Curschmann’s spirals - corkscrew-shaped twists of condensed mucus

- Creola bodies - clusters of surface epithelial cells

- Charcot-Leyden crystals - a pair of hexagonal pyramids joined at their bases. Normally colorless, they are stained purplish-red by trichrome. They consist of lysophospholipase

Differential Diagnosis of Asthma in Children

Congenital conditions

Cystic fibrosis can usually be excluded by:

- negative family history
- normal growth and normal nongreasy stools
- normal CXR

Most children with asthma do not need a sweat chloride or genetic test to rule out cystic fibrosis.

The most common masquerader of asthma is gastroesophageal reflux disease (GERD). GERD triggers wheezing by causing esophagitis rather than aspiration.

Differential Diagnosis of Asthma in Children (click to enlarge the image).

Acquired conditions

Severe asthma in children - different diagnoses and management (click to enlarge the image).

Related reading: Diagnosis of chronic cough in children

Differential diagnosis of asthma in adults

Many congenital conditions are diagnosed before the patient becomes an adult, and therefore the differential diagnosis of asthma in adults consists primarily of acquired conditions.

Beta-blockers can trigger an asthma exacerbation even when used as eye drops for glaucoma or when a selective beta-blocker is taken.

Differential Diagnosis of Asthma in Adults (click to enlarge the image).


Allergy and Immunology MKSAP, 3rd edition.
Links between allergic rhinitis and asthma still reinforced. P. Demoly, P. J. Bousquet (2008). Allergy 63 (3), 251–254.
Recently Updated National Institutes of Health Asthma Treatment Guidelines: Important Clinical Applications, Part 2. Medscape, 11/2008.
APDIM E-Learning Task Force: Cardiac Auscultation, Chest X-Rays, Electrocardiograms, Patient Images (Dermatology), Pulmonary Function Tests, 2009.
Postoperative Tracheal Stenosis. NEJM, 01/2010.
Pulmonary Function Testing. Cleveland Clinic Disease Management Online Textbook.
Assessing Lung Function - a Must in Asthma Therapy http://bit.ly/HBWj7I

Audio and Video

Asthma from a pulmonologist perspective, Dr. Muthiah Muthiah. Podcasting Project for the UT Internal Medicine Residency Program.
Video: Dr. Cherry Wongtrakool Discusses Interpretation of Spirometry Values in Obstructive Lung Disease. InsiderMedicine, 03/2008.
Video: Dr. Cherry Wongtrakool Discusses the Interpretation of Post-bronchodilator Test. InsiderMedicine, 03/2008.
Video: Cherry Wongtrakool, MD Discusses Patterns of Restrictive Lung Disease on Spirometry. InsiderMedicine.

Published: 02/03/2008
Updated: 10/08/2012

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