Diagnosis and Objective Testing

Because many conditions can mimic the symptoms of asthma, guidelines from the European Respiratory Society (ERS) and other major medical bodies emphasize that a diagnosis cannot be based on symptoms alone ^[1]. Objective testing is required to prove that your airways are obstructed and that this obstruction is variable over time ^[2]. When the workplace is involved, testing becomes even more specialized to prove that work is the specific cause ^[3].

The Diagnostic Foundation: Spirometry

The first and most important test for any adult with suspected asthma is spirometry ^[1]. This test measures how much air you can breathe out and how fast you can do it.

• FEV1/FVC Ratio: This number tells your doctor if your airways are narrow or obstructed ^[1].
• Bronchodilator Reversibility (BDR): If obstruction is found, you will be given a “reliever” inhaler and tested again 15 minutes later ^[1]. Depending on the specific medical guideline used, an increase in your FEV1 (the amount of air you can force out in one second) of at least 12% and 200 mL, or a specific percentage of your predicted value, is a strong sign of asthma ^[2].
• Important Caveat: A “normal” spirometry result or a negative reversibility test does not rule out asthma. Because asthma symptoms come and go, your lungs might look fine on the day of the test ^[2][4].

Secondary Tests for Clarification

If your initial spirometry is normal but your doctor still suspects asthma, they will move to other tests ^[1]:

• FeNO (Fractional Exhaled Nitric Oxide): You breathe into a device that measures nitric oxide, a gas produced during Type 2 (allergic) inflammation ^[5]. High levels support a diagnosis of asthma but are not entirely specific to it ^[6].
• Peak Flow Variability: You may be asked to use a small handheld meter to track your Peak Expiratory Flow (PEF) at home. Measuring this several times a day can show the “dips” in lung function that are characteristic of asthma ^[7].
• Bronchial Challenge (Methacholine Test): If other tests are inconclusive, you may be asked to inhale tiny, increasing amounts of a mist that causes slight airway narrowing in people with asthma ^[4]. A negative test reduces the likelihood of asthma, but it does not absolutely rule it out in every clinical circumstance ^[8].

Confirming Occupational Asthma

Standard asthma tests prove you have asthma, but they don’t prove work caused it. To link your asthma to your job, specialists use specific protocols ^[3][9].

Serial Peak Flow Monitoring

This is a common way to link asthma to work. You measure your peak flow multiple times a day for a set period covering both work days and days off, while keeping a diary of your symptoms and exposures ^[10]. Specialists then use software (such as OASYS) to look for patterns where your lung function drops consistently during or after work shifts ^[11].

Allergy Testing (Skin Prick and IgE)

These tests look for antibodies in your skin or blood ^[10]. They are excellent at identifying sensitization to “high-molecular-weight” triggers like flour, grain, or animal proteins ^[12]. However, they are often less effective for “low-molecular-weight” chemical triggers, and being sensitized to a chemical does not necessarily prove it is causing your asthma ^[13]. Safety Data Sheets (SDS) from work can help identify potential triggers, though they may not list every ingredient.

Specific Inhalation Challenge (SIC)

Considered a highly specific test for diagnosis, the SIC is usually performed in a specialized hospital setting ^[14]. You are exposed to a tiny, controlled amount of the suspected workplace trigger while your lung function is monitored ^[3]. This can provide strong evidence of a causal link, but it is not routinely needed, is not available everywhere, and can provoke severe asthma attacks, so it is strictly supervised ^[15].

Organizing Your Evaluation

Instead of checking off a rigid list of tests, you can help your clinician by maintaining a Symptom and Exposure Diary.

• Record the date, your shift times, specific tasks or materials handled, symptoms, your PEF readings, medication use, and days away from work.
• Safety Warning: You should never intentionally expose yourself to a known severe trigger just to generate diagnostic data or prove a point to your doctor or employer.