2026 ICD-10-CM Diagnosis Code R40.2ANontraumatic coma due to underlying condition
R40.2A is a billable ICD-10-CM diagnosis code for nontraumatic coma due to underlying condition. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). The code is not accepted as a principal diagnosis by the Medicare Code Editor. As a symptom code, it should not be used as a principal diagnosis once a related definitive diagnosis has been established. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Coma; stupor; and brain damage.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for R40.2A.
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Inclusion Terms
- Secondary coma
Code First
- underlying condition
Type 1 Excludes
- coma scale, best motor response R40.24
- coma scale, best verbal response R40.22
- coma scale, eyes open R40.21
- Glasgow coma scale, total score R40.23
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.
Certain conditions have both an underlying etiology and multiple body system manifestations due to the underlying etiology. For such conditions, the ICD-10-CM has a coding convention that requires the underlying condition be sequenced first followed by the manifestation. Wherever such a combination exists, there is a "use additional code" note at the etiology code, and a "code first" note at the manifestation code. These instructional notes indicate the proper sequencing order of the codes, etiology followed by manifestation.
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
- nontraumatic, due to underlying condition - R40.2A
- secondary - R40.2A
External Cause of Injuries IndexGuidance
References for this code in the External Cause of Injuries Index.
- Coma
- nontraumatic, due to underlying condition
- Coma
- secondary
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Akinetic Mutism
a syndrome characterized by a silent and inert state without voluntary motor activity despite preserved sensorimotor pathways and vigilance. bilateral frontal lobe dysfunction involving the anterior cingulate gyrus and related brain injuries are associated with this condition. this may result in impaired abilities to communicate and initiate motor activities. (from adams et al., principles of neurology, 6th ed, p348; fortschr neurol psychiatr 1995 feb;63(2):59-67)Brain Death
a state of prolonged irreversible cessation of all brain activity, including lower brain stem function with the complete absence of voluntary movements, responses to stimuli, brain stem reflexes, and spontaneous respirations. reversible conditions which mimic this clinical state (e.g., sedative overdose, hypothermia, etc.) are excluded prior to making the determination of brain death. (from adams et al., principles of neurology, 6th ed, pp348-9)Coma
a profound state of unconsciousness associated with depressed cerebral activity from which the individual cannot be aroused. coma generally occurs when there is dysfunction or injury involving both cerebral hemispheres or the brain stem reticular formation.Coma, Post-Head Injury
prolonged unconsciousness from which the individual cannot be aroused, associated with traumatic injuries to the brain. this may be defined as unconsciousness persisting for 6 hours or longer. coma results from injury to both cerebral hemispheres or the reticular formation of the brain stem. contributing mechanisms include diffuse axonal injury and brain edema. (from j neurotrauma 1997 oct;14(10):699-713)Comamonadaceae
a family of gram-negative aerobic bacteria in the order burkholderiales, encompassing the acidovorans rrna complex. some species are pathogenic to plants.Comamonas
a genus of gram-negative, straight or slightly curved rods which are motile by polar flagella and which accumulate poly-beta-hydroxybutyrate within the cells.Comamonas testosteroni
a species of gram-negative, aerobic rods formerly called pseudomonas testosteroni. it is differentiated from other comamonas species by its ability to assimilate testosterone and to utilize phenylacetate or maleate as carbon sources.Convulsive Therapy
convulsions induced in order to treat mental disorders. it is used primarily in the treatment of severe affective disorders and schizophrenia.Delftia acidovorans
a species of gram-negative rod-shaped bacteria found ubiquitously and formerly called comamonas acidovorans and pseudomonas acidovorans. it is the type species of the genus delftia.Diabetic Coma
a state of unconsciousness as a complication of diabetes mellitus. it occurs in cases of extreme hyperglycemia or extreme hypoglycemia as a complication of insulin therapy.Glasgow Coma Scale
a scale that assesses the response to stimuli in patients with craniocerebral injuries. the parameters are eye opening, motor response, and verbal response.Hepatic Encephalopathy
a syndrome characterized by central nervous system dysfunction in association with liver failure, including portal-systemic shunts. clinical features include lethargy and confusion (frequently progressing to coma); asterixis; nystagmus, pathologic; brisk oculovestibular reflexes; decorticate and decerebrate posturing; muscle spasticity; and bilateral extensor plantar reflexes (see reflex, babinski). electroencephalography may demonstrate triphasic waves. (from adams et al., principles of neurology, 6th ed, pp1117-20; plum & posner, diagnosis of stupor and coma, 3rd ed, p222-5)Hyperglycemic Hyperosmolar Nonketotic Coma
a serious complication of type 2 diabetes mellitus. it is characterized by extreme hyperglycemia; dehydration; serum hyperosmolarity; and depressed consciousness leading to coma in the absence of ketosis and acidosis.Insulin Coma
severe hypoglycemia induced by a large dose of exogenous insulin resulting in a coma or profound state of unconsciousness from which the individual cannot be aroused.Santalaceae
a plant family of the order santalales, subclass rosidae, class magnoliopsida. they are parasites that form connections (haustoria) to their hosts to obtain water and nutrients. the one-seeded fruit may be surrounded by a brightly colored nut-like structure.Frontal Lobe
the part of the cerebral hemisphere anterior to the central sulcus, and anterior and superior to the lateral sulcus.Reticular Formation
a region extending from the pons & medulla oblongata through the mesencephalon, characterized by a diversity of neurons of various sizes and shapes, arranged in different aggregations and enmeshed in a complicated fiber network.Delftia
a genus of gram-negative, strictly aerobic chemoorganotrophic bacteria, in the family comamonadaceae.
Code History & ChangesHistory
Replacement R40.2A replaces the following previously assigned code(s):
- R40.20 - Unspecified coma
Questions About R40.2AOverview
Is R40.2A (Coma) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report nontraumatic coma due to underlying condition on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Can R40.2A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because nontraumatic coma due to underlying condition describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.
