Ask the clinician to answer two questions for a secondary claim, every time: did the service-connected condition cause the second condition, and did it worsen the second condition beyond its natural progress? VA recognizes both routes in 38 C.F.R. § 3.310, paragraphs (a) and (b). An opinion that answers only one of them can leave the claim undecided.

Why you ask for both answers by default

In El-Amin v. Shinseki, 26 Vet.App. 136 (2013), the Court of Appeals for Veterans Claims held that a VA opinion saying a service-connected condition did not cause another condition was not adequate to decide whether it aggravated that condition. The Court noted the examiner's narrow answer traced back to a narrow question in VA's exam request. You can read the opinion on the Court's site.

The Board applies that rule regularly. In a January 2, 2025 decision (Citation A25000331), it remanded a claim for obstructive sleep apnea as secondary to a service-connected lumbar condition. The VA examiner had addressed causation only, and the Board wrote: "A secondary opinion which addresses a causal relationship, but which does not address the question of aggravation, is inadequate." It asked for a new opinion on direct service connection, secondary causation and aggravation, and, if aggravation was found, the baseline level of disability before it. A remand is not a grant; it sent the claim back for a complete opinion.

Asking for both answers up front avoids that delay. It does not mean the clinician has to support both. It means each question gets its own answer and its own reasoning.

Identify both conditions precisely

The packet and the opinion should name:

  • the primary condition VA has already service connected, with the rating decision;
  • the claimed secondary condition and its current diagnosis;
  • the questions asked: causation and aggravation;
  • the records reviewed, by date.

Do not substitute a symptom for a diagnosis unless the question is about the symptom and the clinician explains why it matters.

Causation and aggravation, side by side

A fictional dated record: Sam is service connected for a lumbar spine condition. The file shows:

DateRecordWhat it shows
March 2017Primary care noteHypertension diagnosed; one medication; readings around 138/88
June 2020VA pain clinic noteDaily prescription anti-inflammatory started for the service-connected back
2021 to 2023Primary care notesTwo more blood pressure medications added; readings around 150/95
2024Kidney function testsNormal

The anti-inflammatory could not have caused hypertension that was diagnosed three years before it started. The aggravation question is still open: did the service-connected back condition, through its treatment, worsen the hypertension beyond its natural progress? The March 2017 note is the kind of record that can serve as the baseline.

Now change one fact. If the file showed normal blood pressure through 2020 and a first hypertension diagnosis in 2022, causation would be the main question, and the clinician would need to explain the proposed mechanism, the timing, and other risk factors such as weight, age and family history.

The baseline rule for aggravation

VA will not concede aggravation unless the baseline severity of the non-service-connected condition is established by medical evidence created before the aggravation began, or by the earliest medical evidence created between the onset of aggravation and the evidence showing its current severity. VA then measures the aggravation by subtracting the baseline, and any worsening from the condition's natural progress, from the current level (38 C.F.R. § 3.310(b)). The Federal Circuit held in Spicer v. McDonough (2023) that compensation under 38 U.S.C. § 1110 covers any additional impairment a service-connected disability causes, including a condition that is worse than it would otherwise be, and that § 3.310(b) cannot be used to reject that kind of claim. A dated baseline record still helps the clinician explain how much of the current severity the service-connected condition added.

So the earlier record matters. Include the earliest medical record that shows how severe the second condition was before it worsened. If no record exists before the worsening, include the earliest one created after it. The clinician and VA decide whether the record is enough to set the baseline; the opinion should say which record it used rather than estimating one.

Questions to send the clinician

  1. Is [secondary condition] at least as likely as not caused by service-connected [primary condition], including its treatment?
  2. Separately, is [secondary condition] at least as likely as not aggravated beyond its natural progress by service-connected [primary condition], including its treatment?
  3. If aggravation is found, which dated medical record shows the baseline severity, and how much of the later change reflects the condition's natural progress?
  4. Which competing causes did you consider, and why do they or do not change your answers?

These are review questions. The clinician writes the answers and the reasoning.

What Board data shows about secondary claims

In Claim Raven's analysis of Board decisions, secondary issues were granted less often than direct ones, and more secondary issues were remanded than granted. Direct service connection issues were granted in 41.2% of 40,026 condition records. Secondary issues were granted in 35.1% of 19,189 records and remanded in 41.5%. Opinion quality tracked the outcome closely: secondary records where the Board described the opinion as strong were favorable 94.1% of the time (2,973 records), adequate 68.5% (5,351), weak 1.7% (4,496) and missing 0.5% (2,386).

These are Board appeal outcomes from 2024 to 2025 decisions, a group of already-disputed claims, so they describe patterns, not your odds. The Board's description of an opinion partly reflects its own conclusion, so strong opinions and favorable outcomes are not independent. Secondary connection chains that hold up at the Board and aggravation claims at the Board go further into both routes.

Research supports the opinion; it is not the opinion

A study showing an association between two conditions can make a question worth asking. The clinician still has to explain whether and how it fits this person's history, and note the study population, what was measured and its limits. Statements from a spouse or coworker can help set the timeline of what they saw change, but the medical explanation has to come from the clinician.

Guides for specific secondary conditions

Conditions claimed secondary to PTSD:

Conditions claimed secondary to tinnitus:

Conditions linked to diabetes, medication or weight:

Musculoskeletal, pain and other chains:

Claim Raven's secondary conditions finder lets you look up possible relationships starting from either condition, with a free account.

Check the final letter against the questions

Before relying on the letter, confirm that it answers causation and aggravation separately, names the baseline record if aggravation is found, traces each important fact to a record, deals with the competing causes, and is signed and dated. How to review a nexus letter has a red-flag table for that check.

Raven Nexus can organize the records and research you select into an editable draft and question list for your clinician. A free account includes one starter assessment; full drafts need Standard or Plus, and the clinician provides the medical judgment and signature. Claim Raven sells the tool and has a commercial interest in it.

Secondary nexus letters: common questions

What should a nexus letter for a secondary condition say?

It should answer two questions separately: did the service-connected condition cause the second condition, and did it worsen it beyond its natural progress? It should also name both conditions, the records reviewed, competing causes, and a baseline record if aggravation is found.

Why does a secondary opinion need to address aggravation?

In El-Amin v. Shinseki, the Court of Appeals for Veterans Claims held that an opinion saying a service-connected condition did not cause another condition was not adequate to decide whether it aggravated it. The Board regularly remands claims for that reason.

What is the baseline rule for secondary aggravation?

VA will not concede aggravation unless the baseline severity is established by medical evidence created before the aggravation began, or the earliest medical evidence created after it. VA then subtracts the baseline, and worsening from natural progress, from the current level.

Does Spicer v. McDonough change secondary aggravation claims?

The Federal Circuit held in Spicer v. McDonough that compensation covers any additional impairment a service-connected disability causes, and that § 3.310(b) cannot be used to reject that kind of claim. A dated baseline record still helps the clinician explain how much the service-connected condition added.

What questions should I send my clinician for a secondary claim?

Ask whether the condition is at least as likely as not caused by the service-connected condition, including its treatment; separately, whether it is aggravated beyond natural progress; which record shows the baseline if aggravation is found; and which competing causes were considered.

Is a medical study enough to prove a secondary condition?

No. A study showing an association can make a question worth asking, but the clinician still has to explain whether and how it fits your history, and note the study population, what was measured and its limits.

Sources and scope

Checked September 23, 2026: 38 C.F.R. § 3.310, including the paragraph (b) baseline rule; El-Amin v. Shinseki, 26 Vet.App. 136, 140 (2013) (opinion PDF), a Court of Appeals for Veterans Claims decision; Board decision A25000331 (January 2, 2025, remanded), which applies only to its own record. Board figures are the audited values from Claim Raven's connection-type and opinion-quality fields, counted in condition records. The dated record example is fictional and does not suggest that any medication causes or worsens any condition in a particular person.