M21-1 Manual  /  Part V, Subpart ii, Chapter 2, Section D

Secondary Service Connection (SC) and Aggravation of Non-Service-Connected (NSC) Disabilities

M21-1, Part V, Subpart ii, Chapter 2, Section D

Overview


In This Section

 This section contains the topic “Determining Secondary SC, Including by Aggravation.”

1. Determining Secondary SC, Including by Aggravation

Introduction

 This topic contains information on determining secondary SC, including by aggravation, including
  • provisions for SC under 38 CFR 3.310(a) and (b)
  • establishing causation for secondary SC
  • establishing a baseline to show an NSC disability was aggravated by an SC disability
  • developing for evidence of baseline disability in NSC aggravation claims
  • information that must be included in the examiner’s report for secondary SC based on aggravation
  • handling NSC aggravation claims when a baseline cannot be established
  • assigning an evaluation for an NSC disability that was aggravated by an SC disability, and
  • aggravation with a 0-percent evaluation.

Change Date

 May 1, 2026

V.ii.2.D.1.a. Provisions for SC Under 38 CFR 3.310(a) and (b)

 Award service connection (SC) for the following under the provisions of 38 CFR 3.310(a) and 38 CFR 3.310(b):
  • disabilities that are the result of, or would not have occurred but for, a service-connected (SC) disability, or
  • aggravation of a non-service-connected (NSC) disability that is the result of an SC disability, including
    • any increase in severity of an NSC disability that would not have occurred but for the SC disability, or
    • 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.
Notes:
  • Permanent worsening of an NSC disability by an SC disability is not required to establish SC on the basis of aggravation under 38 CFR 3.310(b).
  • In Spicer v. McDonough, 61 F.4th 1360 (Fed. Cir. 2023), the U.S. Court of Appeals for the Federal Circuit held that the language “resulting from” in 38 U.S.C. 1110 requires a standard of “but-for causation” and that a stricter proximate causation standard is inconsistent with the statute. In accordance with the Spicer holding, the Department of Veterans Affairs (VA) will apply the broader but-for standard and will no longer consider natural progress of the NSC disability when deciding a claim based on aggravation of an NSC disability by an SC disability.
References: For more information on
  • SC for aggravation of NSC disabilities by SC disabilities, see
  • determinations about non-permanent worsening of an NSC disability in claims based on aggravation of an NSC disability by an SC disability, see Ward, Neal v. Wilkie, 31 Vet.App. 233 (2019).

V.ii.2.D.1.b. Establishing Causation for Secondary SC

 SC on a secondary basis requires a showing of causation. A showing of causation requires that the secondary disability is shown to be the result of, or would not have occurred but for, an SC disability. To establish causation, the primary disability need not be SC, or even diagnosed, at the time the secondary disability is incurred. Example: SC was granted for a back disability with radiculopathy effective in 2015. Credible evidence showed that the Veteran had a 20-year history of back pain and progressively worsening radiculopathy dating back to roughly 2001. The formal diagnosis of radiculopathy was not made until 2010. The Veteran claimed SC for a shoulder disability in 2016, stating that his early symptoms of radiculopathy caused him to lose his balance, fall, and tear his rotator cuff in 2008. He provided a medical opinion linking his rotator cuff tear to a fall, and the fall to sensory impairment and difficulty with proprioception due to early symptoms of radiculopathy. Result: As the medical opinion establishes causation for the rotator cuff tear in the shoulder due to the radiculopathy, the requirements for SC on a secondary basis are satisfied.
  • Although the radiculopathy was not formally diagnosed until after the fall, the credible evidence adequately establishes a history of back problems and gradual onset of radiculopathy dating back to 2001. A finding of causation does not require that the primary disability be formally diagnosed at the time the secondary disability is incurred.
  • Additionally, although SC had not been established for the back disability and radiculopathy at the time of the fall and subsequent rotator cuff tear, a finding of causation does not require that the primary disability be SC at the time the secondary disability was incurred.
References: For more information on the
  • establishment of causation prior to a finding of SC or formal diagnosis for the primary disability, see Frost v. Shulkin, 29 Vet.App. 131 (2017), and
  • effective date assigned when a claim for SC for a secondary disability precedes a claim for SC for the primary disability, see M21-1, Part V, Subpart ii, 4.A.3.g.

V.ii.2.D.1.c. Establishing a Baseline to Show an NSC Disability Was Aggravated by an SC Disability

 In order to grant SC on the basis of an NSC disability being aggravated by an SC disability, the baseline level of severity of the NSC disability must be established by
  • medical evidence created before the onset of aggravation
  • the earliest medical evidence created between the
    • onset of aggravation, and
    • receipt of medical evidence establishing the current level of severity of the NSC disability, or
  • any other credible evidence, including lay evidence, that supports establishment of the baseline.
Establishing the baseline (pre-aggravation) level of severity of the NSC disability is necessary to determine which part of the disability can be considered as “resulting from” the SC disability under 38 U.S.C. 1110. Note: Lay evidence, on its own, may not be sufficient to establish the baseline level of severity, but lay evidence can support establishment of the baseline and may trigger the requirement for further development, as discussed in M21-1, Part V, Subpart ii, 2.D.1.d. Important: The baseline level of severity of the NSC disability is required to establish SC and to determine the appropriate evaluation to assign, as discussed in M21-1, Part V, Subpart ii, 2.D.1.g. References: For more information on
  • the requirement to establish a baseline for a grant of SC on the basis of an NSC disability being aggravated by an SC disability, see
  • reviewing and considering lay evidence, see M21-1, Part V, Subpart ii, 1.B.2, and
  • handling NSC aggravation claims when a baseline cannot be established, see M21-1, Part V, Subpart ii, 2.D.1.f.

V.ii.2.D.1.d. Developing for Evidence of Baseline Disability in NSC Aggravation Claims

 The responsibility for submitting evidence to establish a baseline level of disability for a claim for secondary SC based on aggravation of an NSC disability by an SC disability ultimately rests with the claimant. However, VA has a duty to assist the claimant in obtaining evidence necessary to substantiate a claim, which may include requesting an examination and/or medical opinion when warranted. Credible evidence adequate to establish the baseline level of disability must show its level of severity
  • before aggravation by the SC disability, or
  • as soon as possible after aggravation, but before the date of receipt of the evidence establishing the current level of severity of the NSC disability.
Important: Establishment of a baseline level of disability is a legal determination made by the rating activity based on all evidence of record, including the results of any examination and/or medical opinion deemed necessary. When necessary in accordance with the guidance in M21-1, Part IV, Subpart i, 1.B.1.e, request a medical examination and opinion, to include a review of the claims folder by the examiner, to establish whether increased manifestations of the NSC disability are the result of, or would not have occurred but for, an SC disability.

V.ii.2.D.1.e. Information That Must Be Included in the Examiner’s Report for Secondary SC Based on Aggravation

 The examiner’s report must separately address all of the following medical issues in order to be considered adequate for rating a claim for secondary SC based on aggravation:
  • the current level of severity of the NSC disability
  • an opinion as to whether
    • there has been any increase in severity of the NSC disability that would not have occurred but for an SC disability, or
    • the NSC disability would have been less severe but for an SC disability, including where the SC disability has interfered with or impeded treatment for the NSC disability, and
  • an adequate analysis with medical considerations supporting the opinion.
Reference: For more information on requesting examinations for claims based on secondary SC and aggravation, see M21-1, Part IV, Subpart i, 1.B.1.e.

V.ii.2.D.1.f. Handling NSC Aggravation Claims When a Baseline Cannot Be Established

 In accordance with 38 CFR 3.310(b), if no baseline can be established, no aggravation can be demonstrated. When a baseline cannot be established, a claim based on aggravation of an NSC disability by an SC disability must be denied. Important: A claim alleging that an SC disability has aggravated an NSC disability should only be denied based on lack of baseline evidence after VA’s duty to assist has been fulfilled. VA’s duty to assist requires development for evidence regarding the baseline level of severity, which may include requesting an examination and/or medical opinion when warranted. Notes:
  • Do not assume a baseline of 0 percent when a baseline cannot be established by the available evidence.
  • If no baseline can be established after all necessary development efforts are complete, the decision maker should explain in the rating decision Narrative
    • why the degree of aggravation cannot be determined from the available evidence, and
    • that the claim based on NSC aggravation must accordingly be denied.
References: For more information on

V.ii.2.D.1.g. Assigning an Evaluation for an NSC Disability That Was Aggravated by an SC Disability

 When granting SC for an NSC disability on the basis of aggravation by an SC disability, the rating activity must determine the extent of aggravation in order to assign the appropriate evaluation. The evaluation assigned will reflect the difference between the current and baseline levels of severity. To determine the extent to which, if any, an NSC disability was aggravated by an SC disability
  • determine the percentage evaluations that would be warranted for both the baseline and current levels of severity of the NSC disability under the rating schedule, and
  • deduct the baseline level of severity of the NSC disability from the current level to calculate the appropriate evaluation to assign.
Note: This policy applies even when the current level of severity of the NSC disability is 100 percent, including temporary 100-percent evaluations assigned under 38 CFR 4.29 and 38 CFR 4.30.

V.ii.2.D.1.h. Aggravation With a 0-Percent Evaluation

Aggravation of an NSC disability is established by any increase in severity shown to be the result of an SC disability, as discussed in M21-1, Part V, Subpart ii, 2.D.1.a, regardless of whether it would result in a schedular increased evaluation. Whenever there is competent and credible evidence of an increase in severity of the disability from the established baseline, but the current and baseline disability would be assigned the same level of evaluation under the rating schedule, grant SC and assign a noncompensable evaluation. To justify SC, the degree of disability after aggravation does not have to be at least one level of evaluation higher than the baseline. Reference: For more information on determining increased severity for the purpose of establishing aggravation, see

Source: VA M21-1 Adjudication Procedures Manual, M21-1, Part V, Subpart ii, Chapter 2, Section D (U.S. government work, reproduced for reference). Browse all sections →