What is the recommended lab workup and treatment for a patient with a subacute cough, considering potential underlying conditions such as infection, inflammation, or respiratory diseases like asthma or Chronic Obstructive Pulmonary Disease (COPD)?

Laboratory Workup for Subacute Cough

For patients with subacute cough (3-8 weeks duration), routine laboratory testing is generally not indicated; instead, focus on clinical assessment to distinguish postinfectious cough from other treatable conditions, with chest radiography reserved only for suspected pneumonia or red flag symptoms. 1, 2

Initial Clinical Assessment (No Labs Required)

The diagnostic approach to subacute cough is primarily clinical and does not routinely require laboratory workup 1, 2:

• Screen for red flags that would necessitate immediate imaging or specialist referral: hemoptysis, fever with tachypnea, significant dyspnea, weight loss, night sweats, or signs of systemic illness 1, 3
• Verify medication history specifically for ACE inhibitor use, which causes cough in a significant percentage of patients and should be discontinued if present 2, 4
• Assess smoking status and provide cessation counseling if applicable, as smoking exacerbates cough 2, 4
• Determine temporal relationship to recent respiratory infection—if cough began following URI symptoms and has persisted 3-8 weeks, postinfectious cough is the most likely diagnosis 1, 3

When to Order Chest Radiography

Chest X-ray is indicated only in specific circumstances, not routinely 1, 2:

• Clinical findings suggesting pneumonia: tachypnea, abnormal lung sounds (crackles that don't clear with coughing), fever, or hypoxemia 2
• Presence of any red flag symptoms mentioned above 1, 3
• Cough persisting beyond 8 weeks, at which point it becomes chronic cough requiring systematic evaluation 1, 3, 2
• Immunosuppressed patients where infectious causes must be excluded 1

Laboratory Tests: When They Are Actually Needed

Laboratory testing is reserved for specific clinical scenarios, not routine subacute cough 1:

Pertussis Testing

• Consider pertussis PCR or serology when cough lasts ≥2 weeks with paroxysms, post-tussive vomiting, or inspiratory whooping sound 3, 2
• This is particularly important in patients with appropriate exposure history or during known outbreaks 1

Sputum Analysis

• Induced sputum for eosinophil count if non-asthmatic eosinophilic bronchitis (NAEB) is suspected and patient has failed empiric inhaled corticosteroid trial 2
• Sputum culture only if bacterial infection is genuinely suspected (purulent sputum, fever, systemic symptoms)—but note that colored sputum alone does not indicate bacterial infection in postinfectious cough 3

Pulmonary Function Testing

• Spirometry with bronchodilator response if asthma is suspected but not yet diagnosed 2, 5
• Bronchoprovocation challenge if spirometry is normal but asthma or bronchial hyperresponsiveness remains suspected 2
• These tests help distinguish asthma from postinfectious cough, as both can present similarly 1

Common Pitfalls to Avoid

Do not order routine blood work (CBC, CMP, inflammatory markers) for uncomplicated subacute cough, as these provide minimal diagnostic value and increase unnecessary healthcare costs 1, 2

Do not prescribe antibiotics for postinfectious cough—they have no role when the cause is not bacterial infection and explicitly contribute to antimicrobial resistance 1, 3, 6

Do not rely on sputum color to guide antibiotic decisions; green or colored sputum does not indicate bacterial infection in most short-term coughs, which are viral even when producing colored phlegm 3

Do not fail to reassess if cough extends beyond 8 weeks—this requires reclassification as chronic cough and systematic evaluation for upper airway cough syndrome (UACS), asthma, and gastroesophageal reflux disease (GERD) 1, 3, 2

Treatment Algorithm for Subacute Cough

First-Line: Postinfectious Cough Management

If clinical assessment suggests postinfectious cough (most common cause) 1:

1. Inhaled ipratropium bromide 2-3 puffs (17-34 mcg per puff) four times daily—this has the strongest evidence for attenuating postinfectious cough, with response expected within 1-2 weeks 1, 3
2. Supportive care: adequate hydration, rest, honey and lemon for symptomatic relief 3, 4

Second-Line: If Quality of Life Affected

If cough persists despite ipratropium and adversely affects quality of life 1, 3:

• Inhaled corticosteroids (fluticasone 220 mcg or budesonide 360 mcg twice daily) to suppress airway inflammation and bronchial hyperresponsiveness—allow up to 8 weeks for full response 1, 3

Third-Line: Severe Paroxysms Only

Oral prednisone 30-40 mg daily for 5-10 days is reserved exclusively for severe paroxysms that significantly impair quality of life, and only after ruling out UACS, asthma, and GERD 1, 3

Alternative Diagnoses to Consider

If postinfectious cough treatment fails or clinical features suggest otherwise 1, 2:

• Upper airway cough syndrome (UACS): First-generation antihistamine/decongestant combination plus intranasal corticosteroid spray—response typically within days to 1-2 weeks 3, 2
• Asthma: Inhaled bronchodilators and inhaled corticosteroids—response may take up to 8 weeks 3, 2
• GERD: High-dose PPI therapy (omeprazole 40 mg twice daily) with dietary modifications—response may require 2 weeks to several months 3

When to Refer or Escalate Workup

Consider advanced evaluation if all empiric therapies fail 3, 2:

• High-resolution CT chest to evaluate for bronchiectasis, interstitial lung disease, or occult masses 3
• Bronchoscopy to evaluate for endobronchial lesions, sarcoidosis, eosinophilic bronchitis, or occult infection 3
• Referral to pulmonologist or otolaryngologist for refractory cases 5, 7