Nexus letter guide · 6602

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.

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Sample — Illustrative Specimen

Invented veteran · fictional sample provider · not a signed medical opinion

INDEPENDENT MEDICAL OPINION

Veteran: Samuel Okonkwo (invented veteran — illustrative sample)
Condition at issue: Obstructive Sleep Apnea (ICD-10 G47.33)
Service-connected condition relied upon: Chronic Sinusitis (ICD-10 J32.9)
Basis of claim: Secondary service connection under 38 C.F.R. §§ 3.303, 3.310
Opinion date: August 4, 2026

REASON FOR EVALUATION

This is an independent medical opinion prepared for the purpose of assisting in the determination of eligibility for veterans benefits. Its single question is a medical one: whether Mr. Okonkwo's obstructive sleep apnea is proximately due to, the result of, or aggravated beyond its natural progression by his service-connected chronic sinusitis. It is addressed to the C&P examiner and the VA rating official who will weigh it.

MEDICAL OPINION

It is my opinion that it is at least as likely as not (a 50 percent or greater probability) that Obstructive Sleep Apnea is proximately due to, the result of, or aggravated beyond its natural progression by the veteran's service-connected Chronic sinusitis (38 C.F.R. §§ 3.303, 3.310). In short: but for the veteran's service-connected Chronic sinusitis, Obstructive Sleep Apnea would not have occurred, or would not have progressed to its current severity.

Based on the history and records reviewed and the medical literature governing this condition, I opine that Obstructive Sleep Apnea (ICD-10 G47.33) is proximately due to, the result of, or aggravated by his service-connected Chronic sinusitis (ICD-10 J32.9), under 38 C.F.R. § 3.310. This claim is brought as secondary to Chronic sinusitis, established as service-connected in the veteran's VA claims file; the opinion below rests on that anchor. The mechanism connecting the two conditions — chronic nasal and sinonasal obstruction increasing upper-airway resistance and collapsibility during sleep — is well established in the peer-reviewed literature and applies directly to a claimant, like Mr. Okonkwo, whose sinonasal disease began in service and whose obstructive sleep apnea was later confirmed on polysomnography. My opinion accounts for the recognized non-service risk factors for this condition, none of which displaces the sinonasal pathway as at least an equal and materially contributing cause.

Read all 4,348 words — free

The published example letter — an invented veteran and a fictional sample provider.

Key facts

Rated under: 38 CFR § 4.97, DC 6602
Diagnostic code: 6602
The standard: “At least as likely as not” — 50% or greater
Connection theories: Direct (§ 3.303) or secondary (§ 3.310) · 2 pathways below

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.

The standard · 38 CFR § 3.102

“At least as likely as not”

The opinion does not have to be certain, or even “more likely than not.” A 50 percent or greater probability meets the standard; when the evidence is in approximate balance, the benefit of the doubt goes to the veteran.

What a Asthma nexus letter must contain

1
The diagnosis, by name and code
Asthma named as a current, documented diagnosis — the condition the VA rates under 38 CFR § 4.97, DC 6602 (6602). No diagnosis, no service connection: the opinion has to be about a condition that exists in your records.
2
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.
3
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.
4
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%.
5
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:

GERD / Acid RefluxAsthma

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 Reflux

Chronic Sinusitis / RhinitisAsthma

Asthma 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 / Rhinitis

Conditions often claimed secondary to Asthma

Once Asthma is service-connected, conditions it causes or makes worse can be claimed under 38 C.F.R. § 3.310. Each one needs its own nexus opinion explaining that link.

Why 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.

Who can write a Asthma nexus letter

Any licensed clinician qualified to give a medical opinion on Asthma: a physician, or another licensed clinician opining within their field. VA's test is whether the person is qualified by education, training, or experience (38 C.F.R. § 3.159(a)(1)). It does not have to be a VA doctor. Your own treating provider, who already knows your history, is often the strongest choice.

VA Claim Commander drafts the letter from your records and your own words, so your clinician starts from a complete draft; they review it, change what they disagree with, and sign only if it is their opinion.

If your own doctor won't write one, a licensed clinician through Commander Health can review your records and, only if the evidence supports it, write and sign a nexus letter for Asthma. It is a flat $500 that includes the records review, separate from any VA Claim Commander plan, and the clinician can decline if your records don't support an opinion.

Ask your own doctor: draft the request Commander Health nexus letter

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 (38 C.F.R. § 3.159(a)(1) asks for someone qualified by education, training, or experience). 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. If your own doctor won't write one, a licensed clinician through Commander Health can review your records and, only if the evidence supports it, write and sign a nexus letter for Asthma. It is a flat $500 that includes the records review, separate from any VA Claim Commander plan, and the clinician can decline if your records don't support an opinion.

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.

How the VA rates Asthma →Asthma research library →VA disability calculator →

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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.

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Drafts are prepared for review and signature by a licensed clinician. Documentation quality is the promise — never a claim outcome.