A "nexus letter" is a document prepared for a claimant by a medical professional that explicitly connects an in-service event to the current medical condition for which a claimant is seeking compensation. A claimant is not required to submit a nexus letter, but such a letter can make the difference between an award and a denial. A nexus letter can be submitted with an initial application, during claim development, or after an adverse C&P exam. Submitting a properly worded nexus letter as early as possible in the process, however, is good practice.
A nexus letter is especially important in cases where a claimant has not submitted any medical evidence and a C&P examiner concludes that there is no connection between a claimant's condition and military service. Without a nexus letter, the claim will be denied. Even when a claimant supplies supporting medical evidence with an application, VA raters can and often do choose the opinion of the VA examiner over a private physician's opinion for many reasons. In such a case, a "nexus letter" from a private physician is necessary to respond to the C&P examiner's conclusion.
One reason for raters favoring VA examiner's conclusions regarding a nexus when there are conflicting or unclear medical opinions is that VA examiners are more familiar with the terms that raters look for when deciding a claim. As described above, VA regulations require only that it be "at least as likely as not" that a condition be related to service for an award. This means that the likelihood of service connection is equal to or greater than 50% (a 50/50 chance or better).
Most medical professionals, however, are not familiar with the VA system or the VA concept of "at least as likely as not." Physicians are generally familiar with the concept of "medical certainty," which is a much higher standard than that required by VA. As a result, private physicians may apply the wrong standard if the VA terms are not explained to them. Even then, a private physician may be reluctant to state a conclusion regarding nexus and, if they do, may qualify their conclusion with terms such as "may," "could," "suggests," or "possibly." VA will often point to such qualifying terms as not meeting the legal standard for establishing a nexus, although the physician actually believed that the condition was more than 50% likely service connected.
To prevent such misunderstandings, a claimant should make sure that the medical professional asked to provide a nexus letter understands the importance of the letter and of using the VA "magic words" to correctly state the physician's medical opinion. The terms "more likely than not" (meaning greater than 50% likelihood of a connection) and "at least as likely as not" (meaning equal to or greater than 50% likelihood of a connection) are important to use so that VA will have to recognize the nexus letter as supporting service-connection. Any other terms may be misunderstood or misconstrued by VA into something not supporting service-connection. Bringing the relevant C&P Examination Worksheet to the examination or providing it to the medical professional may be helpful.