Ill-defined and unknown cause of mortality (R99)
The ICD-10 code R99 is specifically used to classify deaths where the cause is ill-defined or unknown. This code covers a wide range of situations including sudden infant death, unattended death, and unexpected or unexplained mortality cases where no clear cause has been identified.
R99 helps healthcare providers and medical coders record deaths that cannot be attributed to a specific diagnosis or condition. Synonyms such as “sudden infant death syndrome,” “unattended death,” “death during anesthetic induction,” and “natural death with unknown cause” highlight the variety of scenarios included. This code applies in contexts ranging from hospital inpatients found deceased to deaths occurring outside medical supervision, including perinatal, maternal, and accidental deaths without a definitive cause. By capturing these cases under a single code, R99 facilitates consistent documentation and statistical reporting when postmortem investigations fail to determine an exact cause, ensuring that all deaths with uncertain causes are accurately represented in medical records and mortality data.
Instructional Notations
Inclusion Terms
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
- Death (unexplained) NOS
- Unspecified cause of mortality
Clinical Terms
The following clinical terms provide additional context, helping users better understand the clinical background and common associations for each diagnosis listed in this section. Including related terms alongside ICD-10-CM codes supports coders, billers, and healthcare professionals in improving accuracy, enhancing documentation, and facilitating research or patient education.
Infant
A child between 1 and 23 months of age.
Infant Death
The death of a live-born INFANT within its first year of life.
Maternal Death
The death of the female parent.
Perinatal Death
The death of a FETUS of GESTATIONAL AGE 28 weeks or more, or the death of a live-born INFANT less than 28 days of age.
Sudden Infant Death
The abrupt and unexplained death of an apparently healthy infant under one year of age, remaining unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history. (Pediatr Pathol 1991 Sep-Oct;11(5):677-84)
Sudden Unexpected Death in Epilepsy
Sudden death in a patient with EPILEPSY associated with SEIZURES and seizure-related symptoms (e.g., APNEA; HYPOXEMIA) without other identifiable accidental causes (e.g., DROWNING; WOUNDS AND INJURIES).
