When VA Says a Baseline "Cannot Be Established"

The Denial in Plain English

Aggravation of a non-service-connected condition by a service-connected condition is compensable under 38 CFR § 3.310(b). But that same regulation only pays for the increase above a baseline: the level of severity the non-service-connected condition had before the aggravation began. If VA cannot pin down that baseline, the aggravation theory has nothing to measure the increase against, and the claim is denied on that basis, even when the examiner has confirmed that aggravation occurred.

That is why the letter can look self-contradictory. The concession ("at least as likely as not aggravated") goes to whether aggravation happened. The denial goes to how much, and § 3.310(b) requires a measurable baseline to answer it.

Two Theories, One Difference

The reason the baseline matters at all is that it belongs to only one of the two secondary theories. The difference between them is covered in full here; the short version:

A no-baseline denial is, by definition, a denial of the aggravation theory. It says nothing about whether the causation theory would have required a baseline, because causation does not.

What decides which basis applies

There is no separate "aggravation claim" to file, and the veteran does not choose between the two. It is one secondary service-connection claim under § 3.310, and three things in the record decide which subsection VA applies:

• Whether the condition pre-existed on its own. Causation fits when the service-connected disability created a condition that would not otherwise exist. Aggravation fits when the condition already existed, with its own non-service cause, and the service-connected disability made it worse. Nothing created, something worsened.
• The verb in the medical opinion. This is the practical switch, and it carries real weight. An opinion that says the condition was caused by the service-connected disability is decided under § 3.310(a), where no baseline is required. An opinion that says the condition was aggravated by it is decided under § 3.310(b), which is what brings in the baseline requirement. The same facts can land on either subsection depending on the word the examiner chose.
• Chronology that rules causation out. If the record shows the condition was diagnosed before the service-connected disability could have caused it, causation is off the table and only aggravation remains.

What Spicer Changed

In Spicer v. McDonough, 61 F.4th 1360 (Fed. Cir. 2023), the Federal Circuit read the compensation statute, 38 USC § 1110, to require compensation whenever a service-connected disability is a but-for cause of a present-day disability. The court wrote that the statute "applies to the natural progression of a condition not caused by a service-connected injury or disease, but that nonetheless would have been less severe were it not for the service-connected disability."

Two parts of the ruling bear directly on no-baseline denials:

• The court held § 3.310(b) unlawful "to the extent" VA applies it to reject a but-for theory of compensation the statute requires.
• The court rejected VA's argument that a but-for comparison is too speculative. It reasoned that some speculation is inherent in any but-for causation question, and that VA already performs comparable counterfactual assessments elsewhere in the rating system.

What the Baseline Rules Actually Require

Several requirements sit inside the regulation and VA's own manual that a no-baseline denial can run up against. These are stated in § 3.310(b) and M21-1 Part V.ii.2.D, not synthesized here:

The baseline does not require pre-aggravation records

The regulation allows the baseline to be set "by medical evidence created before the onset of aggravation or by the earliest medical evidence created at any time between the onset of aggravation and the receipt of medical evidence establishing the current level of severity." In other words, the first qualifying medical evidence in the file after onset, an early test result for example, can serve as the baseline. A baseline is not limited to records that predate the worsening.

"VA will not concede that a nonservice-connected disease or injury was aggravated by a service-connected disease or injury unless the baseline level of severity of the nonservice-connected disease or injury is established by medical evidence created before the onset of aggravation or by the earliest medical evidence created at any time between the onset of aggravation and the receipt of medical evidence establishing the current level of severity." (38 CFR § 3.310(b))

The baseline is the rating activity's determination, not the examiner's

Under M21-1, establishing the baseline is a legal determination the rating activity makes from all the evidence of record. It is not a medical conclusion the C&P examiner is asked to reach, and it is not on the manual's examiner-adequacy checklist. A denial that rests entirely on an examiner's statement that a baseline "cannot be established" is resting a rater's legal call on the examiner's plate.

A no-baseline denial is allowed only after development

The manual instructs that a secondary claim should be denied on the aggravation basis for lack of baseline evidence only after VA's duty to assist has been fulfilled, and it directs that raters not assume a baseline of zero percent. The rating decision is expected to explain why the degree of aggravation cannot be determined.

How Veterans Have Approached This Denial

Veterans and their representatives have responded to no-baseline denials in a handful of recurring ways. These are general patterns in how the issue gets framed, not instructions and not predictions about any one claim:

• Reframing around causation. Because § 3.310(a) causation carries no baseline requirement, some veterans focus on whether the record supports that the service-connected condition caused the claimed condition rather than merely worsening it. Where causation fits the facts, the baseline question never arises.
• Questioning the examination. Some responses turn on whether the examination applied the correct legal standard, for example whether the opinion asked the post-Spicer but-for question or an older "proximate cause" test, and whether it engaged with the favorable evidence already in the file.
• Separating the examiner's role from the rater's. Because the baseline is the rating activity's determination, some responses point out that an examiner's inability to state a baseline is not the same as the rater's obligation to establish one from all the evidence.
• Pointing to the earliest evidence in the record. Where an early test result already exists in the file, some veterans note that the regulation permits it to serve as the baseline the denial said was missing.
• Treating the concession as evidence. A denial that concedes aggravation puts that concession into the record, where it remains part of the evidence a later adjudicator weighs.

What the Record Tends to Turn On

Across secondary claims generally, the medical opinions that carry the most weight share a recognizable shape: the examiner reviewed the actual records, stated a specific physiological mechanism linking the two conditions rather than a bare conclusion, and referred to the medical literature supporting that mechanism. An opinion built that way is harder to set aside than a one-line "not related" statement.

Two legal points sit alongside the medical evidence:

• The standard is "at least as likely as not." A 50/50 medical opinion is enough for service connection, and the benefit of the doubt goes to the veteran under 38 CFR § 3.102.
• Favorable evidence has to be addressed. An opinion that ignores supportive evidence already in the file is more vulnerable than one that engages it.

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