Nexus Letter for Asthma: What It Must Say
The medical opinion connecting Asthma (6602) to your service is the piece of the file a rater weighs most heavily. This is what that letter has to contain — and a complete, real example you can read before writing a word.
What a nexus letter is
A nexus letter is a written medical opinion from a licensed clinician stating that a veteran’s condition is “at least as likely as not” (a 50 percent or greater probability) connected to their military service — or to a condition already service-connected. It is the bridge between a diagnosis and service connection: the VA has your diagnosis and your service records, and the nexus opinion is what ties them together with medical reasoning a rater can weigh.
What a Asthma nexus letter must contain
The diagnosis, by name and code
Asthma named as a current, documented diagnosis — the condition the VA rates under 38 CFR Part 4, DC 6602 (6602). No diagnosis, no service connection: the opinion has to be about a condition that exists in your records.
The theory of connection
Direct service connection under 38 C.F.R. § 3.303 (the condition began in or was caused by service), or secondary service connection under § 3.310 (a service-connected condition caused or aggravated it). For Asthma, the secondary path is common — see the mechanisms below — and the letter must name which theory it is using.
The magic words, used correctly
The opinion must be stated to the VA's own standard: "at least as likely as not (a 50 percent or greater probability)." Weaker hedges like "possibly" or "may be related" fail; the standard is a specific legal threshold, and letters that don't invoke it get discounted.
A rationale, not a conclusion
The most common fatal flaw is the conclusory letter — an opinion with no reasoning. A rater is instructed to weigh the rationale: what in the records supports the connection, what the medical literature says about the mechanism, and why known alternative causes don't displace it. For Asthma specifically: Pulmonary function test numbers (FEV-1, FEV-1/FVC) and the medication list — a daily inhaled steroid alone reaches 30%.
A licensed clinician's signature and credentials
The letter is medical evidence only when a licensed clinician — opining within their specialty — reviews it, exercises independent judgment, and signs it with their credentials. VA Claim Commander drafts the letter from your records and your story; your clinician signs it. An unsigned draft is a draft.
Filing Asthma as a secondary condition
Under 38 C.F.R. § 3.310, if a service-connected condition caused or aggravated Asthma, it is service-connected too. The nexus letter’s job becomes explaining the medical mechanism. The pathways veterans most commonly file:
Asthma secondary to GERD / Acid Reflux
Micro-aspiration of gastric acid and vagally mediated bronchoconstriction from esophageal acid exposure directly trigger and worsen asthma symptoms.
What proves it: Pulmonology records documenting asthma; spirometry results; pulmonologist nexus letter discussing the reflux-aspiration mechanism as a cause of asthma exacerbations.
Full guide: Asthma secondary to GERD / Acid RefluxAsthma secondary to Chronic Sinusitis / Rhinitis
Upper and lower airway inflammation are part of one unified airway process; chronic rhinosinusitis frequently drives or worsens co-occurring asthma.
What proves it: Pulmonary function testing or treatment records documenting asthma; ENT or pulmonology nexus describing the unified airway relationship.
Full guide: Asthma secondary to Chronic Sinusitis / RhinitisWhy nexus letters fail
- Conclusory: an opinion with no rationale. The rater is told to weigh reasoning, and a bare “it’s related” weighs nothing.
- Wrong standard: “may be related” or “possibly caused by” instead of “at least as likely as not.”
- Ignores the other causes: a strong letter names the recognized non-service risk factors and explains why they don’t displace the service connection.
- Outside the specialty: a clinician opining far from their field gets less weight than one whose practice covers the condition.
- Unsigned: a draft nobody signed is not medical evidence — it is homework.
Read a complete nexus letter — free, no account
4,348 words, 11 verified studies, the § 3.310 secondary framework — published in full so you can see the standard before you write a word.
Drafts are prepared for review and signature by a licensed clinician. Documentation quality is the promise — never a claim outcome.
Common questions
Do I need a nexus letter for a Asthma VA claim?
If service connection isn't already established for Asthma, a medical nexus opinion is usually the piece a rater weighs most heavily. It connects the diagnosis (6602) to your service — or to an already service-connected condition — using the "at least as likely as not" standard. Presumptive claims are the main exception.
What must a nexus letter for Asthma say?
Four things: the current diagnosis by name and diagnostic code; the connection theory (direct under 38 C.F.R. § 3.303, or secondary under § 3.310); the opinion stated to the "at least as likely as not (50 percent or greater probability)" standard; and a medical rationale grounded in your records and the medical literature — not a bare conclusion. It must be signed by a licensed clinician.
Who has to sign a nexus letter?
A licensed medical professional — a physician, or another clinician opining within their specialty. VA Claim Commander drafts the letter from your own records and story; a licensed clinician reviews, exercises independent judgment, and signs. An unsigned draft is not medical evidence.
Can Asthma be claimed secondary to another condition?
Yes — veterans commonly file Asthma secondary to GERD / Acid Reflux, Chronic Sinusitis / Rhinitis under 38 C.F.R. § 3.310. In a secondary claim, the nexus letter's job changes: instead of connecting Asthma to service directly, it explains the medical mechanism by which the service-connected condition caused or aggravated it.