Key Elements of Diagnosis

To establish a diagnosis of asthma, the clinician should confirm the following key points:

• Episodic symptoms of airflow obstruction are present,
• Airflow obstruction is at least partially reversible, and
• Alternative diagnoses are excluded.

Recommended mechanisms to establish the diagnosis include

• Detailed medical history,
• Physical exam, and
• Measurements of lung function (spirometry or peak expiratory flow) to assess the severity of airflow limitation, its variability, its reversibility and provide confirmation of the diagnosis of asthma.

Additional studies may be needed to diagnosis asthma in children 5 years and younger, in the elderly, and in workers with suspected occupational asthma.

More tests can also be considered to:

• Evaluate alternative diagnoses,
• Identify precipitating factors,
• Assess severity, and
• Investigate potential complications.

Some cases may require referral to a specialist in asthma care for consultation or treatment [NHLBI 2007].

Medical History

The focus of the medical history should be on the presence of any of the following [NHLBI 2007]:

• Cough (particularly worse at night),
• Family history of asthma or allergies,
• Recurrent chest tightness,
• Recurrent difficulty in breathing, and
• Recurrent wheeze.

Note whether symptoms occur or worsen in the presence of [NHLBI 2007]:

• Airborne chemicals or dusts,
• Animals with fur or feathers,
• Changes in weather,
• Dust mites (i.e., in mattresses, pillows, upholstered furniture, carpets, bed linens, stuffed animals; note laundering/cleaning practices involving these items),
• Exercise,
• Menses,
• Mold,
• Pollen,
• Smoke (tobacco, wood),
• Strong emotional expression (laughing or crying hard), or
• Viral infection.

A sample environmental trigger exposure history is included in Appendix 1. This tool was developed by The National Environmental Education and Training Foundation for children and adolescents with asthma [NEETF 2005].

A resource for general exposure history taking is "Case Studies in Environmental Medicine: Taking an Exposure History" https://www.atsdr.cdc.gov/csem/csem.asp?csem=33&po=0

Physical Exam

The physical examination should focus on the:

• Upper respiratory tract (rhino-sinusitis, nasal polyps),
• Chest, and
• Skin (eczema) [NHLBI 2007].

Physical findings that increase the probability of asthma include

• Appearance of hunched shoulders,
• Atopic dermatitis/eczema or any other manifestation of an allergic skin condition,
• Chest deformity,
• Hyperexpansion of the thorax (especially in children),
• Increased nasal secretion, mucosal swelling, and nasal polyps,
• Prolonged phase of forced exhalation (typical of airflow obstruction),
• Sounds of wheezing during normal breathing, and
• Use of accessory muscles of respiration (neck, back, and chest).

Note - Wheezing during forced exhalation is not always a reliable indicator of airflow limitation. In mild intermittent asthma, or between exacerbations, wheezing may be absent.

Pulmonary Function Testing

Spirometry typically measures the maximal volume of air forcibly exhaled from the point of maximal inhalation (forced vital capacity, FVC) and the volume of air exhaled during the first second of the FVC (forced expiratory volume in 1 second, FEV₁). Reduced FEV₁ and FEV₁/FVC values relative to reference or predicted values indicate airflow obstruction.

To help confirm a diagnosis of asthma, take spirometry measurements (Reduced FEV₁ and FEV₁/FVC) before and after the patient inhales a short-acting bronchodilator (200-400 µg salbutamol or albuterol). This helps to determine if the airflow obstruction is reversible over the short term. Spirometry is generally valuable in children over 4 years of age; however, some children cannot conduct the maneuver adequately until after 7 years of age [NHLBI 2007].

An increase of 12% or more and 200 mL or more in FEV₁ after inhaling a short-acting bronchodilator indicates significant reversibility. A 2 to 3-week trial of oral corticosteroid therapy may be required to demonstrate reversibility. The spirometry measures that establish reversibility may not indicate the patient's best lung function. Lung function abnormalities are categorized as restrictive, obstructive, or mixed respiratory impairment.

A reduced ratio of FEV₁/FVC (i.e., < 65%*) indicates obstruction to the flow of air from the lungs.

A reduced FVC with a normal FEV1/FVC ratio suggests a restrictive pattern.

FVC<70% is often taken as the normal cut-off. The normal cut-off is age dependent (falling over time).

The severity of abnormal spirometric measurements is evaluated by comparison of the patient's results with reference values that are based on

• Age,
• Height,
• Race, and
• Sex [NHLBI 2007].

Allergy Testing

For patients with persistent asthma who take daily medications, the clinician should identify allergen exposures and consider using skin testing or in vitro testing to assess sensitivity to perennial indoor allergens.

Determination of sensitivity to a perennial indoor allergen is often not possible from a patient medical history alone.

• Susceptible individuals tend to be atopic and will demonstrate an immediate wheal-and-flare skin reaction when prick-tested against various common allergens.
• Skin testing and in vitro laboratory results (e.g., radioallergosorbent test (RAST testing), which determine antigen-specific IgE concentration in serum, must be correctly interpreted and correlated with the patient's history and exam (see Table 3).
• The enzyme-linked immunosorbent assay (ELISA) is also used. The demonstration of IgE antibodies to an allergen demonstrates prior exposure, but does not always prove that the patient's allergic symptoms are related to that specific allergen [NHLBI 2007].

The recommendation to do skin or in vitro tests for patients with persistent asthma exposed to perennial indoor allergens will result in a limited number of allergy tests for about half of all asthma patients.

• This is based on the prevalence of persistent asthma and the level of exposure to indoor allergens.
• Skin or in vitro tests for patients exposed to perennial allergens are essential to justify the expense and effort involved in implementing environmental controls.
• In addition, patients are less likely to maintain environmental controls (e.g., with regard to pets) without proof of their sensitivity to allergens [NHBLI 2007].

Completely negative skin tests to common allergens are rare in childhood asthma but occur in a substantial proportion of patients with adult-onset asthma [Bonner 1984].

Diagnosis and Evaluation of Occupational Asthma

The adult patient's occupational history is the key diagnostic tool.

• In addition, lung function assessments that include spirometry and bronchial responsiveness are often coupled with immunological assessment and an evaluation of inflammation in the investigation of occupational asthma.
• Evaluations may include serial peak expiratory flow rate (PEFR) measurements and nonspecific hypersensitivity challenges with histamine or methacholine.
• Serial PEFR monitoring while at work and away from work may be important in documenting whether asthma is work-related in selected people, work-environment permitting [Malo and Chan-Yeung 2001].
• Information about workplace exposures to irritants and sensitizers may be useful.
• Specific challenge testing at tertiary referral centers providing specialized laboratories can also be helpful [Rabatin and Cowl 2001] but is rarely necessary and may create unnecessary risk.
• Immunological skin tests may be useful to document immunological sensitization. Induced sputum analysis has been found useful in the assessment of OA [Obata et al. 1999, Lemiere 2004].

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