Baseline Severity: The Make-or-Break Factor in VA Disability Secondary Aggravation Claims

Every week we review denial letters that say the same thing in slightly different words: "Service connection for [condition] as aggravated by [service-connected condition] is denied because a baseline level of severity could not be established."

The veteran reading that letter often did everything they thought was right. They had a real condition, a service-connected disability that made it worse, and sometimes even a doctor who agreed. They still lost. The reason was not the medicine. It was the evidence of what the condition looked like before it got worse.

This post explains what baseline severity is, why it decides so many secondary aggravation claims, how VA's adjudication manual (the M21-1) tells raters to handle it presently, and how to build a claim that survives the VA's baseline analysis.

Two Doors Into Secondary Service Connection

Secondary service connection lives in 38 C.F.R. § 3.310, and it has two distinct paths.

The first path, under § 3.310(a), is causation: your service-connected condition caused a new disability. If service-connected sleep apnea caused hypertension that did not exist before, that is a causation claim.

The second path, under § 3.310(b), is aggravation: you already had a non-service-connected condition, and your service-connected disability made it worse. The regulation provides that any increase in severity of a nonservice-connected disease or injury that is proximately due to or the result of a service-connected disease or injury, and not due to the natural progress of the nonservice-connected disease, will be service connected. eCFR

The aggravation theory traces back to the Court of Appeals for Veterans Claims' en banc decision in Allen v. Brown, 7 Vet. App. 439 (1995), which held that additional disability resulting from the aggravation of a nonservice-connected condition by a service-connected condition is also compensable. VA later codified that principle into § 3.310(b) in a 2006 amendment, and that amendment is where the baseline requirement came from.

The difference between these two doors matters enormously, because aggravation claims carry an evidentiary gatekeeper that causation claims do not.

What the Regulation Actually Requires For SC by Aggravation

Here is the sentence that drives the entire analysis. Under § 3.310(b), 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. eCFR

Read that carefully, because there are three separate requirements hiding inside it.

First, the baseline must come from medical evidence. Your memory of how you felt in 2015 is valuable context, but under the regulation's text it is not what establishes the baseline.

Second, the evidence must be created at the right time: either before the aggravation began, or at the earliest point after aggravation started. A doctor writing today about what your condition was like ten years ago is a weaker substitute than a treatment note written ten years ago.

Third, the evidence must be specific enough to rate. That leads to the calculation itself.

How VA Calculates an Aggravation Rating

Aggravation claims are not rated on the whole condition. They are rated on the increase.

The regulation directs that the rating activity will determine the baseline and current levels of severity under the Schedule for Rating Disabilities (38 CFR part 4) and determine the extent of aggravation by deducting the baseline level of severity, as well as any increase in severity due to the natural progress of the disease, from the current level. eCFR

In plain terms, VA takes three steps. It rates your condition as it was at baseline using the rating schedule criteria. It rates your condition as it is today using the same criteria. Then it subtracts, and you are compensated for the difference.

Consider a simple hypertension example under Diagnostic Code 7101. A veteran's records show diastolic readings consistently in the 100s before his service-connected condition began affecting his blood pressure, which corresponds to a 10 percent level. His current records show diastolic readings consistently of 110 or more, which corresponds to 20 percent. The aggravation award is the 10 percent difference, not the full 20 percent.

Now consider what happens when the baseline and current rating fall in the same bracket. This can be clearly illustrated with a sleep apnea rating senario: a veteran already using a CPAP before the aggravation would already rate at 50% under DC 6847. If the post-aggravation rating is also 50%, the baseline subtraction yields 0% even if aggravation is confirmed. The aggravation is real, the service connection is granted, and the compensation is zero.

This is why baseline severity is not a technicality. It determines both whether you win and how much the win is worth.

The M21-1 After Spicer: What Changed and What Did Not

The most important development in this area in years is the Federal Circuit's decision in Spicer v. McDonough, 61 F.4th 1360 (Fed. Cir. 2023), and VA's implementation of it in the M21-1 in May 2026.

In Spicer, the Federal Circuit rejected VA's narrow reading of secondary aggravation and held that to the extent that the VA also applied 38 C.F.R. § 3.310(b) to reject Mr. Spicer's theory of compensation, that regulation is unlawful as inconsistent with 38 U.S.C. § 1110.

The court read the statutory phrase "resulting from" as a but-for causation standard.

VA's revised manual section, located at M21-1, Part V, Subpart ii, Chapter 2, Section D, now instructs raters to award service connection for disabilities "that are the result of, or would not have occurred but for," a service-connected disability, and for aggravation "where an NSC disability would have been less severe but for the SC disability, including where the SC disability has interfered with or impeded treatment for the NSC disability."

Permanent worsening is not required. The same manual section confirms that permanent worsening is not required. Examiners who deny aggravation because a flare was "temporary" are applying an outdated standard.

Treatment interference now counts. If your service-connected condition prevented, delayed, or complicated treatment for another condition, that can be aggravation. A veteran whose service-connected cardiac condition makes him an unsafe surgical candidate for a joint replacement, for example, now has a recognized theory when the untreated joint deteriorates.

What did not change is the baseline requirement. Even in the revised and updated M21 provisions, the baseline severity rules survive: a claim based on aggravation still requires establishing the pre-aggravation severity of the condition, and if no baseline can be established after VA's duty to assist is met, the manual directs denial. The manual also instructs raters not to assume a baseline of 0 percent.

That last point is critical. VA will not simply treat an undocumented baseline as zero and award you the full current rating. Under current manual guidance, no baseline means no aggravation grant.

Where Baseline Evidence Actually Lives

Most veterans assume they have no baseline evidence. In my experience, most veterans are wrong. The baseline is usually scattered, not missing. Places I routinely find it include:

1. Private primary care and specialist records from before the service-connected condition began affecting the other condition. Blood pressure readings, range-of-motion measurements, A1C values, and symptom descriptions all translate into rating schedule criteria.

   
   

2. VA treatment records, including problem lists, vital signs flowsheets, and nursing intake notes. These are often buried deep in the C-File or in CAPRI records that were never associated with the claim.

   
   

3. Pharmacy and prescription histories. Medication type and dosage are powerful baseline proof. A veteran who controlled hypertension with one low-dose medication in 2018 and now requires three medications has a documented baseline and a documented increase.

   
   

4. Employment, insurance, and occupational health physicals, DOT physicals, life insurance exams, and pre-employment screenings frequently contain objective measurements.

   
   

5. The "earliest medical evidence" safety net. If nothing predates the aggravation, the regulation allows the earliest medical evidence created after aggravation began. This is often the first visit where the condition was documented at all, and it can still anchor a baseline.

   
   

6. Lay statements from the veteran and people who knew them still matter. They establish the timeline of when worsening began and give context to the medical records, even though the regulation calls for medical evidence to fix the baseline itself.

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A Strong Nexus Letter Includes Required Baseline Severity Details For Aggravation Based Secondary Service Connection Claims

A generic nexus letter that says "Condition B is at least as likely as not aggravated by Condition A" is not enough for an aggravation claim. An aggravation nexus letter and independent medical opinion must do the work VA's own exam process requires. A strong private aggravation based medical opinion and/or nexus letter should identify the baseline severity with citation to the specific dated records relied on, describe the current severity in terms that map onto the rating criteria, explain the medical mechanism by which the service-connected disability worsened the other condition, and apply the post-Spicer but-for standard by explaining why the condition would be less severe today but for the service-connected disability. This is especially true and necessary if you are combating or appealing a denial based on a VA examiner's failure to provide a baseline severity.

The Board of Veterans Appeals often finds a VA exam medical opinion inadequate when it addresses causation but fails to properly address aggravation. If your C&P examiner answers only "not caused by," the exam is incomplete, and that is a strong argument for a new exam on Higher-Level Review or BVA appeal.

Strategic Takeaways

Plead both the aggravation and secondary causation theories when the facts allow. If there is any argument that the service-connected disability caused the condition, assert § 3.310(a) causation alongside § 3.310(b) aggravation. A causation grant rates the entire condition with no baseline deduction, which is why the sleep apnea example above can mean the difference between 0 percent and 50 percent. Remember too that the primary disability need not be service-connected, or even diagnosed, at the time the secondary disability was incurred, citing Frost v. Shulkin.

Treat the baseline as the first piece of evidence you gather, not the last. Before the claim is filed, pull the records that document where the condition started.

Scrutinize every denied aggravation decision for three errors: a natural-progression deduction the M21-1 no longer allows, a denial based on "temporary" worsening, and a rater who failed to fulfill the duty to assist before declaring the baseline unascertainable.

The Bottom Line

Secondary aggravation claims are won or lost on evidence documentated in the past. The veteran's condition today may be severe, and the connection to a service-connected disability may be medically obvious, but without a rated baseline, VA's current guidance tells the rater to deny the secondary aggravation claim at the VA Regional Office level.

Veterans who succeed in aggravation claims are the ones whose claims establish, with dated or relevant medical evidence, exactly where the condition stood before the service-connected disability made it worse, and exactly how much it has worsened since aggravation.

If you have been denied for "no baseline," or you are preparing a secondary claim for a condition you had before your service-connected disability took its toll, that denial may not be the end of the story. The evidence is often there. It just has to be found, organized, and argued the right way.

Ready to have your VA case or prior denial reviewed by our VA accredited advocates? Start with our New Client Online Intake Form, or call us at 910-939-8538. Jacksonville Veterans Disability Services proudly serves veterans in all 50 states and worldwide.