C T Deshmukh
Department of Pediatrics, KEM Hospital, Mumbai, India
First Created: 12/21/2000  Last Updated: 05/07/2019

Pointers to Asthma Diagnosis

  • History:
    • Cough (especially in night)

    • Recurrent wheeze (absence does not rule out a diagnosis)

    • Recurrent dyspnea

    • Recurrent chest tightness

    • Atopy

    All the above complaints are classically episodic, nocturnal, seasonal, and exertional atopy.

  • Precipitating or aggravating with specific factors:
    • Airborne chemicals or dust

    • Animals with fur or feathers

    • Changes in weather

    • Exercise

    • House dust mites (mattresses, upholstery, carpets)

    • Menses

    • Nighttime

    • Pollen

    • Smoke (tobacco, wood)

    • Strong emotional expression (laughing, crying)

    • Viral infection

  • Reversibility and variability:
    • Variations in PEFR during the day(>=20%)

    • Reversible symptoms with treatment

If all or some of the above present, confirm the diagnosis by spirometry and response to bronchodilator drugs. If the response is good, asthma is most probable and assess the severity and give appropriate medications. If the response is not good consider other diagnoses or check compliance of anti-asthma drugs.

Asthma - Differential Diagnosis

All that wheezes is not asthma. Alternative or additional diagnosis should be considered when the history is atypical or the response to proper medical treatment is poor. It is important to realize that asthma may often coexist with other conditions.

History not consistent with asthma:

  • Sudden onset of symptoms

  • Coughing or wheezing with feedings

  • Neonatal/early-onset (less than 2-3 months)

  • Neonatal requirement for ventilatory support

  • Symptoms of stridor

  • Vomiting/choking

Signs not consistent with asthma:

  • Clubbing (cystic fibrosis, bronchiectasis, interstitial lung disease, congenital heart disease)

  • Activity level

  • Failure to thrive and vomiting

  • Productive cough

  • Speech - hoarseness

  • Stridor or choking

  • Ability to speak or cry normally-(infant and young child)

  • Focal lung signs

  • CVS signs

  • Chronic infection

A large number of conditions can result in symptoms suggestive of asthma. Common conditions to be considered in atypical cases include:

  • Laryngol-tracheomalacia

  • Foreign bodies in airway or esophagus

  • Chronic viral infections (including HIV related infections of the lungs)

  • Bronchiolitis

  • Endobronchial tuberculosis

  • Pertussis

  • Croup

  • Aspiration syndromes

  • Bronchiectasis

  • Immuno-deficiency diseases

  • Cystic fibrosis

  • Tropical Eosinophilia

  • Congenital anomalies of Respiratory, gastrointestinal or cardiovascular systems

The differential diagnosis of the child with wheezing can be approached on an age group basis. Infants are at a higher risk for congenital abnormalities and most infectious conditions. Aspiration of a foreign body and cystic fibrosis may occur most commonly early in life but can be seen at any age. GER with pulmonary involvement may occur at any age but more common in smaller children. Vocal cord dysfunction and the hyperventilation syndrome merit consideration mainly in the adolescent age group.

Asthma - Investigations

The investigations to be considered are chest x-rays, sinus x-rays, lung function tests, bronchial challenge tests, Mantoux test, sweat test, immune function studies, ciliary studies, and reflux studies. Along with these studies, response to bronchodilator therapy should also be assessed. If the response is good and other tests are negative then consider asthma alone or in association with other diseases.

Peak expiratory flow rate/Spirometry: Objective measurement of pulmonary function is important whenever possible not only to confirm the clinical diagnosis but to monitor asthma as well. Patient’s subjective symptoms and doctor’s subjective assessment correlate poorly with pulmonary functions and declines in pulmonary functions may predate acute deteriorations in asthma. This has been stressed in the new guidelines for the management of asthma. Expiratory spirometry should be used as soon as the child is old enough to cooperate. Peak flow monitoring and pulmonary function measurements can generally be done by age 6 or 7 years and in some children peak flow measured as young as 3 to 4 years old.

Peak expiratory flow rate (PEFR):

  • Peak expiratory flow rate (PEFR) is the fastest rate at which air can move through the airways during forced expiration.

  • And can be easily measured by a simple device the peak flow meter.

  • The peak flow during forced exhalation occurs after about 25% of the vital capacity has been exhaled. It does not require a complete exhalation like a spirometer, even a dyspneic patient is able to perform the test.

  • PEFR provides a simple, quantitative measure of airflow obstruction, which can be performed in the home, school, workplace for a quick measure of lung function.

  • PEFR should be done at least once a day in all individuals who have more than mild asthma severity. PEFR can provide a direct assessment of airflow limitations, diurnal variation, and reversibility. The test should be done in the morning and compared with the patient’s best effort.

  • Patient’s best effort is taken as the average reading is taken when the patient is asymptomatic over a period of 2-3 weeks.

PEFR measurements instructions:

  1. Place indicator at the base of the scale
  2. Stand up and take a deep breath
  3. Place meter in mouth and close lips around the mouthpiece
  4. Blow out as hard as possible (same as blowing a balloon)
  5. Write down achieved measurement
  6. Repeat process two more times
  7. Record the highest of the values achieved

Reinforcement of proper technique at every visit is important. Same PEFR meter to be used by the patient at all times. Good control is maintaining PEFR at above 80-90% of normal. A drop in more than 50-60% is an indication that the attack is severe and medical help may be needed. Daily monitoring can also help in monitoring environmental triggers.


The findings in asthma are:

  • Increased total lung capacity, functional residual capacity, and residual volume.

  • Decrease in vital capacity

  • Decreased dynamic tests of airflow i.e. FEV1, FVC, Maximum expiratory flow between 25-75% of vital capacity
  • FEV1 is considered the single best measure of lung function to assess asthma severity. FEV25-75 is used to assess the function of smaller airways in children.

Indications for spirometry:

  • At the time of initial diagnosis

  • After the patient has stabilized on treatment

  • At least 1-2 yearly for a periodic check on PEFR in moderate to severe asthmatics

  • When reducing the dosage of medications

Other Investigations:

  • Hemogram: Leucocytosis may indicate infection, the stress of severe asthma, and can be seen in excessive use of epinephrine. Eosinophilia may not necessarily mean an allergic etiology.

  • A chest x-ray should be obtained at least once in any child with asthmatic symptoms sufficient to require hospitalization.

  • X-ray of the sinuses when needed.

  • Sweat Test: Child who has had several exacerbations of asthma requiring in-hospital treatment or who has had a history of recurrent pneumonia should be considered a candidate for a sweat chloride test to rule out cystic fibrosis.

  • Children with recurrent wheezing who have repeated bronchopneumonia confirmed by x-ray film should have an immunologic evaluation, including quantitative immunoglobulins and possibly specific antibody titers.

  • The determination of specific IgE antibody by skin or in vitro tests is useful to evaluate potential allergic trigger factors in children with asthma or when a history suspicious of atopic etiology is obtained. Allergy testing in vitro or skin testing should be done in moderate to a severe asthmatic.

  • Electrolytes: Hypokalemia due to beta2 agonists.

  • Arterial blood gases are important when the patient is admitted with a severe exacerbation. The changes seen in asthma depends on the severity:

    • Initial changes - decrease PaO2 & decrease PaCO2

    • Moderate severity - decrease PaO2 & increase or normal PaCO2

    • Severe - decrease pH, decrease PaO2 & increase PaCO2

  • Eosinophil cationic protein (ECP) and eosinophil-derived neurotoxin (EDN) can be used in the diagnosis ad follow up of patients. The urinary concentration of eosinophil-derived neurotoxin can be especially valuable in young children because in this age group quantification of lung function cannot be performed and blood sampling can be a difficulty.

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Asthma Asthma 2019-05-07
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