2026 ICD-10-CM Diagnosis Code T59.0X4AToxic effect of nitrogen oxides, undetermined, initial encounter
T59.0X4A is a billable ICD-10-CM diagnosis code for toxic effect of nitrogen oxides, undetermined, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 917 through 918. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under External cause codes: intent of injury, undetermined; External cause codes: poisoning by non-drug; and Toxic effects, initial encounter.
Code Identity
Code Classification
Coding GuidelinesGuidance
The appropriate 7th character is to be added to each code from block Toxic effect of other gases, fumes and vapors (T59). Use the following options for the applicable episode of care:
- A - initial encounter
- D - subsequent encounter
- S - sequela
Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Blood Urea Nitrogen
the urea concentration of the blood stated in terms of nitrogen content. serum (plasma) urea nitrogen is approximately 12% higher than blood urea nitrogen concentration because of the greater protein content of red blood cells. increases in blood or serum urea nitrogen are referred to as azotemia and may have prerenal, renal, or postrenal causes. (from saunders dictionary & encyclopedia of laboratory medicine and technology, 1984)Dissolved Organic Matter
a heterogeneous class of water-soluble compounds containing covalently bound carbon that are derived from a variety of biological and geological sources during the biogeochemical cycling of carbon (carbon cycle).Inert Gas Narcosis
progressive mental disturbances and unconsciousness due to breathing mixtures of oxygen and inert gases (argon, helium, xenon, krypton, and atmospheric nitrogen) at high pressure.Lasers, Gas
lasers in which a gas lasing medium is stimulated to emit light by an electric current or high-frequency oscillator.Mannomustine
nitrogen mustard derivative alkylating agent used as antineoplastic. it causes severe bone marrow depression and is a powerful vesicant.Mechlorethamine
a biologic alkylating agent that exerts its cytotoxic effects by forming dna adducts and dna interstrand crosslinks, thereby inhibiting rapidly proliferating cells. the hydrochloride is an antineoplastic agent used to treat hodgkin disease and lymphoma.N-Glycosyl Hydrolases
a class of enzymes involved in the hydrolysis of the n-glycosidic bond of nitrogen-linked sugars.Nitric Oxide
a free radical gas produced endogenously by a variety of mammalian cells, synthesized from arginine by nitric oxide synthase. nitric oxide is one of the endothelium-dependent relaxing factors released by the vascular endothelium and mediates vasodilation. it also inhibits platelet aggregation, induces disaggregation of aggregated platelets, and inhibits platelet adhesion to the vascular endothelium. nitric oxide activates cytosolic guanylate cyclase and thus elevates intracellular levels of cyclic gmp.Nitrogen
an element with the atomic symbol n, atomic number 7, and atomic weight [14.00643; 14.00728]. nitrogen exists as a diatomic gas and makes up about 78% of the earth's atmosphere by volume. it is a constituent of proteins and nucleic acids and found in all living cells.Nitrogen Compounds
inorganic compounds that contain nitrogen as an integral part of the molecule.Nitrogen Cycle
the circulation of nitrogen in nature, consisting of a cycle of biochemical reactions in which atmospheric nitrogen is compounded, dissolved in rain, and deposited in the soil, where it is assimilated and metabolized by animals, plants, bacteria, and fungi, eventually returning to the atmosphere by bacterial decomposition of organic matter.Nitrogen Dioxide
nitrogen oxide (no2). a highly poisonous gas. exposure produces inflammation of lungs that may only cause slight pain or pass unnoticed, but resulting edema several days later may cause death. (from merck, 11th ed) it is a major atmospheric pollutant that is able to absorb uv light that does not reach the earth's surface.Nitrogen Fixation
the process in certain bacteria; fungi; and cyanobacteria converting free atmospheric nitrogen to biologically usable forms of nitrogen, such as ammonia; nitrates; and amino compounds.Nitrogen Isotopes
stable nitrogen atoms that have the same atomic number as the element nitrogen but differ in atomic weight. n-15 is a stable nitrogen isotope.Nitrogen Mustard Compounds
a group of alkylating agents derived from mustard gas, with the sulfur replaced by nitrogen. they were formerly used as toxicants and vesicants, but now function as antineoplastic agents. these compounds are also powerful mutagens, teratogens, immunosuppressants, and carcinogens.Nitrogen Oxides
inorganic oxides that contain nitrogen.Nitrogen Radioisotopes
unstable isotopes of nitrogen that decay or disintegrate emitting radiation. n atoms with atomic weights 12, 13, 16, 17, and 18 are radioactive nitrogen isotopes.Nitrogenase
an enzyme system that catalyzes the fixing of nitrogen in soil bacteria and blue-green algae (cyanobacteria). ec 1.18.6.1.Nitrogen-Fixing Bacteria
bacteria that are capable of nitrogen fixation.Nitrogenous Group Transferases
enzymes that catalyze the transfer of nitrogenous groups, primarily amino groups, from a donor, generally an amino acid, to an acceptor, usually a 2-oxoacid. ec 2.6.Nitrous Oxide
nitrogen oxide (n2o). a colorless, odorless gas that is used as an anesthetic and analgesic. high concentrations cause a narcotic effect and may replace oxygen, causing death by asphyxia. it is also used as a food aerosol in the preparation of whipping cream.PII Nitrogen Regulatory Proteins
a family of signal transducing adaptor proteins that control the metabolism of nitrogen. they are primarily found in prokaryotes.Reactive Nitrogen Species
nitrogenous products of nitric oxide synthases, ranging from nitric oxide to nitrates. these reactive nitrogen intermediates also include the inorganic peroxynitrous acid and the organic s-nitrosothiols.
Table of Drugs and ChemicalsClinical
Patient EducationClinical
Poisoning
A poison is any substance that is harmful to your body. You might swallow it, inhale it, inject it, or absorb it through your skin. Any substance can be poisonous if too much is taken. Poisons can include:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T59.0X4A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T59.0X4AOverview
Is T59.0X4A (Toxic effect of nitrogen oxides, undetermined) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report toxic effect of nitrogen oxides, undetermined, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T59.0X4A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for toxic effect of nitrogen oxides, undetermined, such as an emergency visit or first evaluation.
What MS-DRG does T59.0X4A group to?
When toxic effect of nitrogen oxides, undetermined, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 917, 918, with relative weights from 0.8571 to 1.5684 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of T59.0X4A?
Under the General Equivalence Mappings, toxic effect of nitrogen oxides, undetermined, initial encounter converts to ICD-9-CM 987.2 (toxic eff nitrogen oxide) and E982.8 (undet pois-gas/vapor NEC). The mapping is approximate, so confirm the match fits the documentation.
Footnotes
[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.
