A
The final slide in this sequence provides the official Diagnostic Algorithm B (NG245), updated in late 2024. This is the "gold standard" workflow clinicians must follow to diagnose asthma in children and young people (ages 5–16).
The core message here is that subjective clinical history must be backed by objective evidence.
The Diagnostic Logic Tree (Step-by-Step)
The algorithm follows a "cascade" approach. If one test is positive, the diagnosis is confirmed; if not, you move to the next test.
1. FeNO (The Inflammation Marker)
Question: Is the FeNO level 35 ppb or more?
If Yes: Confirm diagnosis.
If No (or test unavailable): Move to Spirometry.
2. Spirometry with BDR (The Obstruction Test)
Question: Is there reversible airflow obstruction?
Threshold: An increase in $FEV_1$ of 12% or more from baseline.
If Yes: Confirm diagnosis.
If No (or BDR unavailable): Move to Peak Flow.
3. Peak Expiratory Flow (The Variability Test)
Question: Is the "amplitude percentage mean" (variability) 20% or more?
If Yes: Confirm diagnosis.
If No: Move to Allergy/Blood Testing.
4. Sensitisation (The Allergic Component)
Question: Is there evidence of sensitization (e.g., positive Skin Prick Test for house dust mites) OR is total IgE raised?
The Final Filter: If these are also negative, clinicians must check the Eosinophil count. If it's $\ge$ 0.5 x $10^9$ per litre, the diagnosis can be confirmed.
Closing the Loop on Chloe and Muhammad
Using this official algorithm, we can see why Professor Turner used those two children as examples:
Chloe: She was "caught" at the very first box. Her FeNO was 38 ppb ($\ge$ 35), so the clinician stops there. Diagnosis confirmed.
Muhammad: He "failed" the first box (FeNO was 28 ppb). The clinician then has to move through the rest of the boxes—Spirometry, Peak Flow, and Sensitisation—to see if he "trips" any other positive markers.
Critical Takeaway: "Consider Alternative Diagnoses"
If a child goes through this entire cascade and answers "No" to every box, the algorithm (the far right green box) explicitly instructs the clinician to Consider alternative diagnoses. This is a major shift designed to prevent children with other conditions (like habit cough or reflux) from being incorrectly treated with long-term steroids.
Final Summary of the 2025/2026 Guidelines
Symptoms First: You only start the algorithm if there is a "history suggestive of asthma" (Cough, Wheeze, DIB).
Objective Proof: You need at least one "Yes" from the objective tests to make the label permanent.
Specialist Input: If the tests are negative but you still strongly suspect asthma, refer to a pediatric specialist for a "bronchial challenge test."
Would you like me to create a printable "pocket guide" summary of these thresholds for quick reference?
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