Coding Corner

ICD-10 codes are fundamental in substantiating the medical necessity of a service. Each code corresponds to a specific diagnosis or condition that a health care provider is treating. When submitting claims to insurance companies or Medicare, providers must correctly include these codes to justify the need for certain treatments or procedures.

An authorization is not a guarantee of payment, and providers are required to adhere to the coding and billing reporting guidelines.

Please see example below for a scenario in which ICD-10 codes are reported as the ONLY diagnosis on a claim (the primary diagnosis on a professional claim or principal diagnosis on a facility claim).

• Example: First code the underlying disease, such as, Pachydermoperiostosis (M89.4). L62 (this ICD-10 code describes Nail disorders in diseases classified elsewhere) is not accepted as a primary diagnosis because instructions require the underlying condition to be coded first.

The residual or late effect of an injury generally requires two codes. The primary diagnosis must describe the nature of the sequela. The secondary diagnosis describes the original injury and usually has an “S” in the 7th position to indicate sequela. (Sequela of cerebrovascular disease is an exception.) See the example below:

• Primary Diagnosis: Treatment of ankle instability following a sprain: M24.271 (this is the ICD-10 code for Disorder of ligament, right ankle)
• Secondary Diagnosis: S93.411S - Sprain of calcaneofibular ligament, right ankle, sequela S93.411S is not accepted as a primary diagnosis because instructions require the residual condition be coded first.

Below are some additional diagnoses and their definitions:

• External Causes Diagnosis - These codes are supplements to the principal or primary diagnosis code indicating the nature of the condition.
• Manifestation Diagnosis – ICD-10-CM convention requires the underlying condition sequenced first followed by the manifestation.
• Secondary Diagnosis – A "secondary only" ICD-10-CM code refers to a diagnostic code that can only be used as a secondary diagnosis and cannot be listed as the primary diagnosis on a claim; meaning it should always be accompanied by another primary diagnosis code when billing medical services.
• Sequela Diagnosis - According to the ICD-10-CM Manual guidelines, a sequela (seventh character "S") code is not appropriate as a primary, first listed, or principal diagnosis on a claim.
• Laterality Policy: Laterality is a unique attribute to the ICD-10-CM code set built into certain ICD-10-CM code descriptions.

Sources:

1. PA Health & Wellness. (2023, October 25). Clinical Policy: Medical Necessity Guidelines. Retrieved from PA Health & Wellness
2. Centers for Medicare and Medicaid Services. (2024, October 1). ICD-10-CM Guidelines FY25. Retrieved from CMS.gov
3. Novitas. (2021, December 10). Medically Necessary Services and Prior Authorization. Retrieved from Novitas Solutions