What blood work is indicated for a 10-year-old with chronic cough and no yield of diagnosis (NYD)?

Blood Work for a 10-Year-Old with Chronic Cough NYD

For a 10-year-old with chronic cough of unknown diagnosis (NYD), routine blood work is not recommended as a first-line investigation. Instead, a chest radiograph and spirometry should be the initial diagnostic tests 1, 2.

Initial Diagnostic Approach

1. Chest radiograph - Mandatory first-line investigation 1, 2
2. Spirometry (pre- and post-β2 agonist) - Essential for children this age 1
3. Clinical assessment for specific cough pointers - To guide further testing 1

When to Consider Blood Work

Blood work should be targeted based on specific clinical pointers rather than performed routinely. Consider specific blood tests only when the following are present:

Specific Indications for Blood Tests:

• Suspected pertussis: Pertussis serology if clinically suspected (paroxysmal cough, post-tussive vomiting) 1, 2
• Suspected immunodeficiency: Complete blood count, immunoglobulin levels if recurrent infections or family history 1
• Suspected allergic disease: IgE levels, eosinophil count if strong history of atopy 1
• Suspected inflammatory condition: ESR/CRP if systemic inflammation suspected 1

What NOT to Do

• Do not routinely perform additional tests (skin prick test, Mantoux, bronchoscopy, chest CT) without specific clinical indications 1
• Do not order extensive blood panels without clear clinical pointers 1
• Avoid empirical treatment approaches without establishing a diagnosis 1, 2

Diagnostic Algorithm

1. Define chronicity: Confirm cough has persisted >4 weeks 1

2. Characterize the cough: Wet/productive vs. dry, timing, associated symptoms 2

3. Perform chest radiograph and spirometry 1

4. Look for specific cough pointers:

   • Productive/wet cough → Consider protracted bacterial bronchitis
   • Wheezing/exercise-induced symptoms → Consider asthma
   • Paroxysmal cough → Consider pertussis
   • Digital clubbing, failure to thrive → Consider bronchiectasis, CF

5. Order targeted blood work only if specific pointers present

Important Considerations

• Most common causes of chronic cough in children include protracted bacterial bronchitis, asthma, and post-viral cough 1, 2
• The etiology varies based on clinical setting and population studied 1
• In children, unlike adults, GERD and upper airway cough syndrome are less commonly identified as causes of chronic cough 1
• Chronic cough can significantly impact quality of life and may indicate serious underlying conditions requiring prompt diagnosis 2

Remember that a systematic approach using validated guidelines is more valuable than extensive blood testing in determining the cause of chronic cough in children 1.