is_icd: Is ICD

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

Is ICD

Description

Answer the question "is the character string x a valid ICD code?" ICD codes should be character vectors. is_icd will assess for both "full codes" (decimal point present when appropriate) and "compact codes" (decimal point omitted).

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

is_icd(
  x,
  icdv = c(9L, 10L),
  dx = c(1L, 0L),
  src = c("cms", "who", "cdc"),
  year,
  headerok = FALSE,
  ever.assignable = missing(year),
  warn.ambiguous = TRUE,
  full.codes = TRUE,
  compact.codes = TRUE
)

Arguments

x	Character vector of ICD codes (full or compact form).
icdv	Integer vector of allowed ICD versions. Use 9L and/or 10L. Defaults to both.
dx	Integer vector indicating allowed code type(s): 1L for diagnostic (ICD-9-CM, ICD-10-CM, CDC mortality, WHO), 0L for procedural (ICD-9-PCS, ICD-10-PCS). Defaults to both.
src	Character vector of code sources. One or more of "cms", "who", "cdc". Defaults to all.
year	Numeric scalar. Calendar or fiscal year to reference. Default is the most current year available per source. For ICD-9, CMS data run through fiscal year 2015 and CDC extracts through 2012; ICD-10 sources are updated annually. Calendar year for WHO and CDC mortality. Fiscal year for CMS.
headerok	Logical scalar. If FALSE (default), only assignable codes are considered valid; if TRUE, header codes are also accepted.
ever.assignable	Logical scalar. If TRUE then ignore year and return TRUE if the x was ever an assignable code.
warn.ambiguous	Logical scalar. If TRUE (default), warn when a code matches more than one ICD version and/or type (e.g., both CM and PCS).
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.

Details

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 logical vector the same length as x.

See Also

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

• lookup_icd_codes() for retrieving details on a specific set of ICD codes.

• 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(), lookup_icd_codes()

Examples

################################################################################
# Some ICD-9 diagnostic codes
x <- c("136.2", "718.60", "642.02")

is_icd(x, icdv =  9, dx = 1)
is_icd(x, icdv =  9, dx = 0)
is_icd(x, icdv = 10, dx = 1)
is_icd(x, icdv = 10, dx = 0)

is_icd(x, icdv = 9, dx = 1, headerok = TRUE)
is_icd(x, icdv = 9, dx = 1, year = 2006)

################################################################################
# ICD code with, or without a dot.  The ICD-9 diagnostic code 799.3 and ICD-9
# procedure code 79.93 both become 7993 when assessed against the ICD code look
# up tables.  As such "7993" is a valid ICD-9 diagnostic and procedure code,
# whereas 799.3 is only a valid dx code, and 79.93 is only a valid pr code.
# Further, codes such as ".7993", "7.993", "7993.", are all non-valid codes.

x <- c("7993", ".7993", "7.993", "79.93", "799.3", "7993.")
data.frame(
  x,
  dx = is_icd(x, icdv = 9, dx = 1),
  pr = is_icd(x, icdv = 9, dx = 0)
)

################################################################################
# example of a ICD-9 code that was assignable, but became a header when
# more descriptive codes were introduced: ICD-9 diagnostic code 516.3
lookup_icd_codes(paste0("516.3", c("", as.character(0:9))))

# ICD-9 code 516.3 was an assignable code through fiscal year 2011.
is_icd("516.3")

# If `year` is omitted, and `ever.assignable = FALSE` then the `year` is
# implied to be the max `known_end` year for ICD codes matched by `icdv`,
# `dx`, and `src`.
is_icd("516.3", ever.assignable = FALSE)

# when `year` is provided then `ever.assignable` is `FALSE` by default and
# the return is TRUE when 516.3 was assignable and FALSE otherwise.
is_icd("516.3", year = 2015)
is_icd("516.3", year = 2011)

# when year is a non-assignable year, but `ever.assignable = TRUE` the return
# will be TRUE.  Useful if you know the data is retrospective and collected
# through fiscal year 2015.
is_icd("516.3", year = 2015, ever.assignable = TRUE)

################################################################################
# Consiser the string E010
#   - This could be a ICD-9-CM full code
#   - Could be a ICD-10-CM compact code
lookup_icd_codes("E010")
subset(get_icd_codes(with.descriptions = TRUE), grepl("^E010$", code))

is_icd("E010")
is_icd("E010", icdv = 9) # FALSE because it is a header code and was never assignable
is_icd("E010", icdv = 9, ever.assignable = TRUE) # FALSE
is_icd("E010", icdv = 9, headerok = TRUE) # TRUE

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