lookup_icd_codes: Lookup ICD Codes

In medicalcoder: A Unified and Longitudinally Aware Framework for ICD-Based Comorbidity Assessment

Lookup ICD Codes

Description

Functions for working with ICD codes.

ICD-10 code "C00" is a header code because the four-character codes C00.0, C00.1, C00.2, C00.3, C00.4, C00.5, C00.6, C00.7, C00.8, and C00.9 exist. Those four-character codes are assignable (as of 2025) because no five-character descendants (e.g., C00.40) exist.

When the source is the World Health Organization (WHO) or CDC Mortality, years refer to calendar years. CDC/CMS sources use the U.S. federal fiscal year, which starts on October 1 (e.g., fiscal year 2024 runs 2023-10-01 to 2024-09-30).

Usage

lookup_icd_codes(
  x,
  regex = FALSE,
  full.codes = TRUE,
  compact.codes = TRUE,
  ...
)

Arguments

x	Character vector of ICD codes (full or compact form). When regex = TRUE, x must contain at least one non-empty, non-missing string.
regex	Logical scalar. If TRUE, treat x as regular expressions; if FALSE, use exact matching.
full.codes	Logical scalar. If TRUE (default), match codes that include the decimal point where applicable.
compact.codes	Logical scalar. If TRUE (default), match codes without the decimal point.
...	Passed to base::grep() when regex = TRUE

Details

ICD codes should be character vectors. These tools work with either "full codes" (decimal point present when appropriate) or "compact codes" (decimal point omitted).

Similarly for ICD-9-CM: "055" is a header for measles; 055.0, 055.1, 055.2, 055.8, and 055.9 are assignable. Codes 055.3–055.6 do not exist. Code 055.7 is a header because 055.71 and 055.72 exist.

Some codes change status across years. For example, ICD-9-CM 516.3 was assignable in fiscal years 1997–2011 for the CDC extracts (2006–2011 for CMS) and became a header in 2012–2015.

Value

A data.frame with one or more rows per input, including columns

• match_type: did the input match a full or compact code

• icdv: icd version (9 or 10)

• dx: diagnostic code (1) or procedure code (0)

• full_code: the full code string

• code: the compact codes string

• src: the source - CMS, CDC, or WHO.

• year ranges (⁠known_*⁠, ⁠assignable_*⁠).

See Also

• get_icd_codes() to retrieve the internal lookup table of ICD codes.

• is_icd() to test if a string is a known ICD code.

• icd_compact_to_full() converts a string from a compact format to the full format based on ICD version and type (diagnostic or procedure).

Other ICD tools: icd_compact_to_full(), is_icd()

medicalcoder documentation built on Feb. 22, 2026, 5:08 p.m.