What Blood Tests Are Done for Asthma? Complete 2026 Lab Panel Guide

Author: Dr Sagar Rajkuwar (MS-ENT), ENT Specialist, Nashik, Maharashtra, India
🌐 www.entspecialistinnashik.com

If your doctor has mentioned a blood panel for suspected asthma, you may wonder exactly what blood tests are done for asthma, what they measure, and why they matter. This comprehensive 2026 guide covers every blood test commonly ordered — from the humble complete blood count to advanced biomarkers that guide biologic therapy. Based on GINA 2024, NHS, CDC, and American Thoracic Society recommendations.

Featured Infographic

📑 Table of Contents

1. Introduction: Why Blood Tests Matter in Asthma
2. Complete Blood Count (CBC) and Eosinophil Count
3. Total Immunoglobulin E (IgE)
4. Specific IgE Tests (RAST)
5. C-Reactive Protein (CRP) and ESR
6. Serum Vitamin D Level
7. Periostin — The Emerging Biomarker
8. Arterial Blood Gas (ABG) in Severe Asthma
9. BNP / NT-proBNP (Rule Out Cardiac Asthma)
10. Thyroid Function Tests (TFT)
11. Alpha-1 Antitrypsin
12. ANCA, ANA (Rule Out Vasculitis)
13. Aspergillus-Specific IgE and IgG (ABPA Screen)
14. Blood Tests for Biologic Therapy Eligibility
15. Interpretation Matters: What’s Normal vs Abnormal
16. When Should Blood Tests Be Repeated?
17. Children vs Adults
18. FAQs on What Blood Tests Are Done for Asthma
19. Summary
20. Conclusion
21. Medical Disclaimer
22. References

1. Introduction: Why Blood Tests Matter in Asthma

Asthma is primarily diagnosed through clinical history and spirometry, but blood tests play a critical supportive role. Patients frequently ask what blood tests are done for asthma because the right lab panel can:

• Identify the asthma phenotype (allergic, eosinophilic, non-allergic).
• Guide choice of medication, including biologics.
• Rule out mimics like cardiac failure, vasculitis, or infection.
• Monitor severity and response to treatment.
• Detect comorbidities that worsen asthma.

2. Complete Blood Count (CBC) and Eosinophil Count

The single most important answer to what blood tests are done for asthma is: CBC with differential, especially the eosinophil count.

• Normal eosinophil count: 50–500 cells/µL.
• ≥300 cells/µL: suggests eosinophilic asthma phenotype.
• ≥500 cells/µL: strong indicator for biologic eligibility.
• Also measures: hemoglobin (anemia), WBC (infection), platelets.

Eosinophilia strongly predicts response to inhaled corticosteroids (ICS) and biologic agents like mepolizumab, reslizumab, and benralizumab.

3. Total Immunoglobulin E (IgE)

When discussing what blood tests are done for asthma, total serum IgE is a classic marker for allergic (atopic) asthma.

• Normal adult range: <100 kU/L.
• Elevated in allergic asthma, atopic dermatitis, parasitic infections.
• Required for calculating omalizumab (Xolair) dose: formula uses weight × IgE.
• Very high (>1000 kU/L): consider ABPA, hyper-IgE syndrome.

4. Specific IgE Tests (RAST)

Among all tests addressing what blood tests are done for asthma, specific IgE panels (also called RAST — radioallergosorbent test — or newer ImmunoCAP) identify individual allergens:

• Dust mites (Dermatophagoides pteronyssinus)
• Cat dander (Fel d 1)
• Dog dander
• Grass pollens (timothy, Bermuda)
• Tree pollens (birch, oak)
• Weed pollens (ragweed)
• Mold spores (Alternaria, Aspergillus, Cladosporium)
• Cockroach allergens
• Food allergens (eggs, milk, peanuts — rarely trigger asthma alone)

Levels classified by CAP class 0 to 6 based on quantitative measurement.

5. C-Reactive Protein (CRP) and ESR

When exploring what blood tests are done for asthma, inflammation markers like CRP and ESR help rule out infection or coexisting inflammatory conditions.

• Elevated CRP during acute exacerbation suggests bacterial infection.
• Persistently elevated inflammatory markers warrant investigation for vasculitis or ABPA.
• Serial measurements may help in treatment monitoring.

6. Serum Vitamin D Level

Vitamin D (25-OH) is now routinely included when asking what blood tests are done for asthma.

• Normal: 30–100 ng/mL.
• Deficiency (<20 ng/mL): associated with:
  • Worse asthma control
  • Higher exacerbation rates
  • Lower response to ICS
• Supplementation may improve outcomes in deficient patients.

7. Periostin — The Emerging Biomarker

Among newer biomarkers in the list of what blood tests are done for asthma:

• Periostin is a matricellular protein secreted by airway epithelial cells in response to IL-13.
• Elevated levels indicate Th2-high eosinophilic inflammation.
• Used in research and some centers to predict response to lebrikizumab and other anti-IL-13 therapies.
• Not yet universally available in all labs.

8. Arterial Blood Gas (ABG) in Severe Asthma

When exploring what blood tests are done for asthma during a severe exacerbation, ABG analysis is critical.

• pH, PaO2, PaCO2, HCO3-, SpO2.
• Early severe asthma: low PaO2, low PaCO2 (hyperventilation).
• Impending respiratory failure: normal or rising PaCO2 — ominous sign requiring urgent intervention.
• Metabolic acidosis may occur in severe cases.

9. BNP / NT-proBNP (Rule Out Cardiac Asthma)

Another vital test when asking what blood tests are done for asthma in elderly or atypical presentations:

• B-type Natriuretic Peptide (BNP): elevated in heart failure.
• Normal: < 100 pg/mL.
• Levels > 400 pg/mL strongly suggest heart failure (cardiac asthma).
• NT-proBNP: similar significance; different cutoffs by age.
• Essential when considering cardiac asthma differential.

10. Thyroid Function Tests (TFT)

Sometimes included in panels addressing what blood tests are done for asthma:

• TSH, Free T4, Free T3.
• Hyperthyroidism can mimic or worsen asthma (tachycardia, dyspnea).
• Hypothyroidism may cause fatigue and reduced exercise tolerance confused with asthma.
• Especially relevant when evaluating refractory or new-onset symptoms.

11. Alpha-1 Antitrypsin

In unusual cases, when exploring what blood tests are done for asthma:

• Alpha-1 antitrypsin deficiency can cause early-onset emphysema and asthma-like symptoms.
• Blood level and genotyping test.
• Especially consider in non-smokers with early COPD or chronic airflow limitation.

12. ANCA, ANA (Rule Out Vasculitis)

Among specialized tests considered under what blood tests are done for asthma:

• Eosinophilic granulomatosis with polyangiitis (EGPA) — formerly Churg-Strauss syndrome — presents as refractory asthma + eosinophilia + sinusitis + neuropathy.
• p-ANCA (MPO-ANCA) positive in ~40% of EGPA.
• ANA, dsDNA: to screen for other connective tissue diseases.
• Essential in refractory asthma with multisystem features.

13. Aspergillus-Specific IgE and IgG (ABPA Screen)

Vital set of tests when evaluating what blood tests are done for asthma in patients with poor control:

• Aspergillus-specific IgE: elevated in allergic bronchopulmonary aspergillosis (ABPA).
• Aspergillus-specific IgG precipitins: supports chronic ABPA.
• Total IgE > 1000 ng/mL: cardinal feature of ABPA.
• Peripheral eosinophilia often marked.

14. Blood Tests for Biologic Therapy Eligibility

Modern severe asthma care increasingly uses biologics. These tests directly answer what blood tests are done for asthma patients being considered for biologic therapy:

• Blood eosinophil count ≥ 150/µL (for mepolizumab, reslizumab, benralizumab).
• FeNO (not blood, but relevant) ≥ 25 ppb (for dupilumab).
• Total serum IgE (for omalizumab dosing).
• Specific IgE to perennial allergens (for omalizumab eligibility).
• Hepatitis B/C screen: before starting biologics or oral steroids.
• Latent TB screening: Mantoux, IGRA — important before some biologics.

15. Interpretation Matters: What’s Normal vs Abnormal

Here is a summary table addressing what blood tests are done for asthma and their reference ranges:

16. When Should Blood Tests Be Repeated?

When discussing what blood tests are done for asthma, patients often ask about repetition:

• Eosinophil count: every 6–12 months for severe asthma or when considering biologics.
• IgE: once at baseline; repeat if changing biologic therapy.
• Vitamin D: annually, especially in deficient patients.
• Specific IgE: at baseline; not routinely repeated unless environment changes.
• ABG: only during severe exacerbations.
• CRP: during suspected infective exacerbations.

17. Children vs Adults

Pediatric considerations for what blood tests are done for asthma:

• Eosinophil count: higher reference in children.
• Total IgE: age-dependent reference ranges.
• Blood sampling is less frequent in young children — only when clinically needed.
• Specific IgE: often favored over skin testing in very young or those on antihistamines.

18. FAQs on What Blood Tests Are Done for Asthma

Q1. Can asthma be diagnosed by blood tests alone?

No. Blood tests support but do not diagnose asthma. Diagnosis requires objective testing like spirometry with reversibility.

Q2. Why is eosinophil count so important in asthma?

Because elevated eosinophils identify the eosinophilic phenotype, which responds very well to inhaled corticosteroids and modern biologic therapies.

Q3. What is the difference between total IgE and specific IgE?

Total IgE measures all IgE antibodies in blood; specific IgE identifies allergic sensitization to individual allergens.

Q4. Do I need fasting for asthma blood tests?

Most asthma blood tests do not require fasting. Confirm with your lab or physician.

Q5. Can inhalers affect blood test results?

Inhaled steroids can lower blood eosinophil counts; mention your medications when getting tested.

Q6. What does high periostin mean?

Elevated periostin suggests Th2-driven, eosinophilic inflammation that may respond to anti-IL-13 therapies.

Q7. Is ABG necessary for every asthma patient?

No. ABG is reserved for severe acute exacerbations or when respiratory failure is suspected.

Q8. How much does an asthma blood panel cost in India?

Varies by lab and panel: a basic CBC + IgE panel ranges ₹500–₹1500; specific IgE panels ₹2000–₹8000 depending on number of allergens; BNP ₹1500–₹3000.

Q9. Can blood tests show how severe my asthma is?

Partially. Eosinophil count and FeNO levels correlate with inflammation; but severity is best assessed by symptoms, lung function, and exacerbation frequency.

Q10. Will I need lifelong blood monitoring?

Not usually. Baseline testing plus periodic monitoring (annually or during biologic therapy) is typical.

19. Summary

Answering what blood tests are done for asthma, the most important ones are: CBC with eosinophil count, total serum IgE, specific IgE, vitamin D, and CRP. For severe or atypical cases, add BNP, ANCA/ANA, Aspergillus-specific IgE, and periostin. For biologic therapy, eosinophil count and IgE guide eligibility and dosing. ABG is reserved for emergencies.

20. Conclusion

Knowing what blood tests are done for asthma helps you understand your condition deeper and participate in care decisions. Blood tests complement spirometry and clinical history to build a complete diagnostic picture, identify your phenotype, and personalize treatment — especially the choice between standard inhalers and advanced biologic agents. Always have your results interpreted by a qualified physician.

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Dr. Sagar Rajkuwar (MS-ENT)
Prabha ENT Clinic, Ambad, Nashik

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21. Medical Disclaimer

Medical Disclaimer: This article is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. The blood tests described must be ordered and interpreted by a qualified physician. Individual test choice and interpretation depend on symptoms, physical examination, and other investigations. Do not self-order laboratory tests or start/stop medications based solely on this content. Seek medical attention for persistent respiratory symptoms.

22. References

1. Global Initiative for Asthma (GINA) — Global Strategy for Asthma Management and Prevention, 2024 Update. https://ginasthma.org/
2. WHO — Asthma Fact Sheet. https://www.who.int/news-room/fact-sheets/detail/asthma
3. NHS UK — Asthma Tests. https://www.nhs.uk/conditions/asthma/
4. CDC — Asthma Resources. https://www.cdc.gov/asthma/
5. American Thoracic Society — Biomarkers in Severe Asthma.
6. European Respiratory Society (ERS) — Guidelines on biologic therapy in severe asthma.
7. NICE Guideline NG80 — Asthma diagnosis and management.