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).
lookup_icd_codes(
x,
regex = FALSE,
full.codes = TRUE,
compact.codes = TRUE,
...
)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_*).
Character vector of ICD codes (full or compact form).
Logical scalar. If TRUE, treat x as regular
expressions; if FALSE, use exact matching.
Logical scalar. If TRUE (default), match codes that
include the decimal point where applicable.
Logical scalar. If TRUE (default), match codes without
the decimal point.
Passed to base::grep() when regex = TRUE
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 2006–2011, then became a header in 2012–2015.
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()