The first part of the test requires that there is a current diagnosis of a medical condition or disability. This means that a healthcare professional must provide a formal diagnosis indicating the existence of the condition. The diagnosis should provide clarity on the nature and extent of the medical condition for which the veteran is seeking disability benefits. Here are key aspects of what the "current diagnosis" should include:

Specific Medical Condition: The diagnosis should clearly identify the specific medical condition for which the veteran is seeking disability benefits. It should use standard medical terminology to describe the nature of the condition.

Medical Professional's Credentials: The diagnosis should be provided by a qualified healthcare professional. This professional may include physicians (MDs or DOs), psychologists, psychiatrists, or other specialists depending on the nature of the condition.

Date of Diagnosis: The diagnosis should include the date on which the healthcare professional formally diagnosed the medical condition. The date is important for establishing the timeframe of the condition's existence.

Clinical Findings and Observations: The diagnosis should include relevant clinical findings and observations that support the identification of the medical condition. This may involve a summary of symptoms, examination results, and any diagnostic tests performed.

ICD Code (if applicable): In some cases, the diagnosis may be associated with an International Classification of Diseases (ICD) code. The ICD code is a standardized system used for classifying and coding diseases and conditions. The diagnosis should provide information on the severity of the medical condition and any functional limitations it imposes on the veteran. This information is crucial for determining the appropriate disability rating.

Stability or Progression: If applicable, the diagnosis may include information on the stability or progression of the medical condition. This can be important for assessing the long-term impact of the condition.

Relevance to Military Service: While the diagnosis itself may not explicitly address military service, its relevance to the in-service incident or aggravation should be clear. This connection is crucial for meeting the VA three-part test criteria.

Compliance with Standard Medical Practice: The diagnosis should comply with standard medical practice and follow established medical guidelines. It should be a well-supported and evidence-based determination.

Signature and Date: The diagnosis should be signed and dated by the healthcare professional providing it. The signature authenticates the document, and the date indicates when the diagnosis was made.

The second part of the test involves establishing a link between the current diagnosis and an incident, injury, or event that occurred during the veteran's military service. The medical condition should either have originated during military service or been significantly aggravated by the service.

"In-Service Incident or Aggravation" refers to an event or circumstance that occurred during a veteran's military service and is linked to the development or worsening of a medical condition or disability. To meet the second criterion of the VA three-part test for service connection, the in-service incident or aggravation must have a direct connection to the current medical condition for which the veteran is seeking disability benefits. Here's a detailed description of what qualifies as an in-service incident or aggravation:

In-Service Incident:

• Occurrence During Service: An in-service incident is an event or exposure that took place while the veteran was on active duty. It could be a specific injury, trauma, or exposure to environmental factors that contributed to the development of the current medical condition.

• Examples of In-Service Incidents:

  • Combat-related injuries or wounds sustained during military operations.

  • Accidents or physical injuries that occurred during training exercises.

  • Exposure to harmful substances or environmental hazards during deployment.

• Documentary Evidence: Veterans may provide service records, incident reports, or other documentation that establishes the occurrence of the in-service incident.

Aggravation of Pre-existing Conditions:

• Worsening of a Pre-existing Condition: Aggravation refers to the worsening or exacerbation of a pre-existing medical condition during military service. If a condition that existed prior to service was significantly worsened by military service, it may be considered service-connected.

• Examples of Aggravation:

  • A pre-existing back injury that becomes more severe due to the physical demands of military service.

  • Aggravation of a mental health condition due to the stresses of military duty.

• Medical Evidence: To establish aggravation, medical evidence is crucial. This may include medical records showing the progression or worsening of the condition during service and expert medical opinions linking the aggravation to specific incidents or conditions during military service.

Continuous Symptoms and Post-Service Manifestation:

• Continuous Symptoms: For conditions that may not have been diagnosed during service but have continuous symptoms, the veteran must demonstrate that the symptoms began during or shortly after military service.

• Post-Service Manifestation: Some conditions may manifest or become diagnosable only after the veteran has left military service. In such cases, the veteran must establish a clear connection between the current diagnosis and the in-service incident or aggravation.

• Medical Opinions: Expert medical opinions may be necessary to establish a connection between the in-service incident or aggravation and the current medical condition, especially when symptoms or diagnoses occur after service.

The third part of the test involves establishing a medical nexus or linkage between the current diagnosis and the in-service incident or aggravation. A medical professional, often a doctor or healthcare specialist, must provide a reasoned opinion or statement connecting the veteran's current medical condition to the specific incident or aggravation during military service. 

"Medical Nexus or Linkage" refers to the third criterion of the VA three-part test for service connection. It involves establishing a direct connection or link between the current diagnosed medical condition and the in-service incident or aggravation. A medical professional, often a doctor or healthcare specialist, plays a crucial role in providing a reasoned opinion or statement that connects the veteran's current medical condition to the specific incident or aggravation during military service. Here's a detailed description of what qualifies as a medical nexus or linkage:

• Expert Medical Opinion:

  • Qualified Healthcare Professional: A medical nexus requires an opinion from a qualified healthcare professional. This professional is typically a doctor who is knowledgeable about the veteran's specific medical condition and its potential connections to military service.

  • Specialists: In some cases, specialists may be necessary, especially when dealing with complex or specialized medical conditions. For example, a psychiatrist may provide an opinion for mental health conditions.

• Causation Analysis:

  • Analysis of Cause and Effect: The medical professional conducts a causation analysis, examining the relationship between the in-service incident or aggravation and the current medical condition. This involves assessing whether there is a logical and direct connection between the two.

  • Consideration of Medical Literature: The medical professional may consider relevant medical literature, research studies, and recognized medical principles in forming their opinion. This adds credibility to the nexus statement.

• Review of Service Records, Examination of Military Service History: The medical professional reviews the veteran's military service records, including documentation of the in-service incident or aggravation. Understanding the context and details of the military service is essential for establishing a connection.

• Detailing the Nexus in Medical Opinion:

  • Clear Articulation: The medical professional provides a clear and articulate opinion, detailing how the current medical condition is related to the in-service incident or aggravation. The opinion should address causation, the progression of the condition, and any relevant medical factors.

  • Supporting Rationale: The medical opinion includes a supporting rationale that explains the basis for the professional's conclusion. This may involve explaining the biological mechanisms linking the condition to the in-service event.

• Submission of Medical Evidence, Inclusion in the VA Claim File: The veteran submits the expert medical opinion as part of the evidence supporting their claim for service connection. It becomes a crucial component of the VA claim file.