What is ICD-9 Coding?

The International Classification of Diseases Clinical Modification, 9th Revision (ICD-9 CM) is a list of codes intended for the classification of diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or disease. The numerical format of the diagnosis codes usually ranges from three to five digits that are assigned to a unique category.

The two departments within the U.S. Federal Government’s Department of Health and Human Services that provide the guidelines for coding and reporting ICD-9 codes are the Centers for Medicare and Medicaid Services and the National Center for Health Statistics.

Assigning ICD-9 CM codes to a patients is important because they are recorded and used for morbidity and mortality statistics, reimbursement systems, and automated decision support in medicine. Keep in mind that an incorrect diagnosis can affect a patient’s medical coverage. Physicians and coders should pay close attention to accurate documentation, code assignments, and reporting of diagnoses, signs, or symptoms that are included in a patient’s medical record.

The ICD-9 CM consists of:

  • A tabular list of the numerical disease codes;
  • An alphabetical index to the disease entries; and
  • A classification system for surgical, diagnostic, and therapeutic procedures as an alphabetic index and tabular list.

The ICD is revised annually and the 10th revision will go into effect October 1, 2013. Annual minor updates and three-year major updates are published by the World Health Organization. A list of commonly used diagnosis codes in rheumatology is available on the ACR website as a supplement to the ICD-9 manual, but should not be used independently.

General Diagnosis Coding Guidelines

  • The ICD-9 book is updated on October 1 of each year
    • The new codes are effective on October 1, and insurance carriers will reject all claims made after that date that have outdated diagnosis codes.
  • When coding diagnoses, the coder should use both the alphabetic index and the tabular list from the ICD-9 book.
    • Relying on only the alphabetic section or the tabular list can lead to errors when assigning a diagnosis code. Not cross-checking between the two sections can lead to incorrect coding or not reaching the highest level of specificity in the code selection.
  • A coder should locate the medical term in the alphabetic index first.
    • After finding the term in the alphabetic index, the code should be verified in the tabular section before billing the claim.
  • Always code to the highest level of specificity.
    • It is not acceptable to code for signs and symptoms if there is an established diagnosis listed in the medical records or findings.
    • ICD-9 diagnosis codes contain three, four, or five digits. The three-digit code is the heading of a section of codes that are further divided by more detailed fourth and fifth digits.Example:
      • 274 – Gout
        • 274.0 – Gouty arthropathy
          • 274.00 – Gouty arthropathy, unspecified

The patient’s medical record should be documented with all diagnoses. The claim can be denied or downcoded based on unsubstantiated diagnoses. Diagnosis codes are usually what support the medical necessity of charges that are billed. When a carrier states that a charge was denied for not being medically necessary, this means the diagnosis does not fit the treatment, according to their medical policy for that particular procedure. The carrier will not tell a coder what diagnoses to use for the procedure, but that can be found in the medical policy of the procedure or drug being used.

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