2026 ICD-10-CM Diagnosis Code T45.2X6AUnderdosing of vitamins, initial encounter
ICD-10-CM T45.2X6A
T45.2X6A is a billable ICD-10-CM diagnosis code for underdosing of vitamins, 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). The code is not accepted as a principal diagnosis by the Medicare Code Editor. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Underdosing of drugs and medicaments, initial encounter.
Code Identity
ICD-10-CM Code
T45.2X6A
Billable Status
Yes — Valid for Submission
Code Describes
Underdosing of vitamins, initial encounter
Short Description
Underdosing of vitamins, initial encounter
Same as the full description in the CMS dataset.
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T45.2X6A.
There are selected codes that describe a circumstance which influences an individual's health status but not a current illness or injury, or codes that are not specific manifestations but may be due to an underlying cause. These codes are considered unacceptable as a principal diagnosis.
Coding GuidelinesGuidance
Underdosing refers to taking less of a medication than is prescribed by a provider or a manufacturer's instruction. Codes for underdosing should never be assigned as principal or first-listed codes. If a patient has a relapse or exacerbation of the medical condition for which the drug is prescribed because of the reduction in dose, then the medical condition itself should be coded.
The appropriate 7th character is to be added to each code from block Poisoning by, adverse effect of and underdosing of primarily systemic and hematological agents, not elsewhere classified (T45). 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.
CCSR INJ029
Underdosing of drugs and medicaments, initial encounter
Default principal diagnosis: inpatient No · outpatient No
Clinical InformationClinical
Adenine
a purine base and a fundamental unit of adenine nucleotides.Adenine Nucleotide Translocator 1
a subtype of mitochondrial adp, atp translocase found primarily in heart muscle (myocardium) and skeletal muscle (muscle, skeletal).Adenine Nucleotide Translocator 2
a subtype of mitochondrial adp, atp translocase found primarily in fibroblasts.Adenine Nucleotide Translocator 3
a subtype of mitochondrial adp, atp translocase found primarily in the liver.Adenine Nucleotides
a class of nucleotide translocases found abundantly in mitochondria that function as integral components of the inner mitochondrial membrane. they facilitate the exchange of adp and atp between the cytosol and the mitochondria, thereby linking the subcellular compartments of atp production to those of atp utilization.Adenine Phosphoribosyltransferase
an enzyme catalyzing the formation of amp from adenine and phosphoribosylpyrophosphate. it can act as a salvage enzyme for recycling of adenine into nucleic acids. ec 2.4.2.7.Deoxyadenosines
adenosine molecules which can be substituted in any position, but are lacking one hydroxyl group in the ribose part of the molecule.Mitochondrial ADP, ATP Translocases
a class of nucleotide translocases found abundantly in mitochondria that function as integral components of the inner mitochondrial membrane. they facilitate the exchange of adp and atp between the cytosol and the mitochondria, thereby linking the subcellular compartments of atp production to those of atp utilization.NAD
a coenzyme composed of ribosylnicotinamide 5'-diphosphate coupled to adenosine 5'-phosphate by pyrophosphate linkage. it is found widely in nature and is involved in numerous enzymatic reactions in which it serves as an electron carrier by being alternately oxidized (nad+) and reduced (nadh). (dorland, 27th ed)Poly A
a group of adenine ribonucleotides in which the phosphate residues of each adenine ribonucleotide act as bridges in forming diester linkages between the ribose moieties.Vidarabine
a nucleoside antibiotic isolated from streptomyces antibioticus. it has some antineoplastic properties and has broad spectrum activity against dna viruses in cell cultures and significant antiviral activity against infections caused by a variety of viruses such as the herpes viruses, the vaccinia virus and varicella zoster virus.Vidarabine Phosphate
an adenosine monophosphate analog in which ribose is replaced by an arabinose moiety. it is the monophosphate ester of vidarabine with antiviral and possibly antineoplastic properties.Ascorbic Acid
a six carbon compound related to glucose. it is found naturally in citrus fruits and many vegetables. ascorbic acid is an essential nutrient in human diets, and necessary to maintain connective tissue and bone. its biologically active form, vitamin c, functions as a reducing agent and coenzyme in several metabolic pathways. vitamin c is considered an antioxidant.Ascorbic Acid Deficiency
a condition due to a dietary deficiency of ascorbic acid (vitamin c), characterized by malaise, lethargy, and weakness. as the disease progresses, joints, muscles, and subcutaneous tissues may become the sites of hemorrhage. ascorbic acid deficiency frequently develops into scurvy in young children fed unsupplemented cow's milk exclusively during their first year. it develops also commonly in chronic alcoholism. (cecil textbook of medicine, 19th ed, p1177)Biotin
a water-soluble, enzyme co-factor present in minute amounts in every living cell. it occurs mainly bound to proteins or polypeptides and is abundant in liver, kidney, pancreas, yeast, and milk.Biotinidase
an enzyme which catalyzes the release of biotin from biocytin. in human, defects in the enzyme are the cause of the organic acidemia multiple carboxylase deficiency or biotinidase deficiency.Biotinidase Deficiency
the late onset form of multiple carboxylase deficiency (deficiency of the activities of biotin-dependent enzymes propionyl-coa carboxylase, methylcrotonyl-coa carboxylase, and pyruvate carboxylase) due to a defect or deficiency in biotinidase which is essential for recycling biotin.Biotinylation
incorporation of biotinyl groups into molecules.Myoclonic Epilepsies, Progressive
a heterogeneous group of primarily familial epilepsy disorders characterized by myoclonic seizures, tonic-clonic seizures, ataxia, progressive intellectual deterioration, and neuronal degeneration. these include lafora disease; merrf syndrome; neuronal ceroid-lipofuscinosis; sialidosis (see mucolipidoses), and unverricht-lundborg syndrome.Calcifediol
the major circulating metabolite of vitamin d3. it is produced in the liver and is the best indicator of the body's vitamin d stores. it is effective in the treatment of rickets and osteomalacia, both in azotemic and non-azotemic patients. calcifediol also has mineralizing properties.Calcitriol
the physiologically active form of vitamin d. it is formed primarily in the kidney by enzymatic hydroxylation of 25-hydroxycholecalciferol (calcifediol). its production is stimulated by low blood calcium levels and parathyroid hormone. calcitriol increases intestinal absorption of calcium and phosphorus, and in concert with parathyroid hormone increases bone resorption.Receptors, Calcitriol
proteins, usually found in the cytoplasm, that specifically bind calcitriol, migrate to the nucleus, and regulate transcription of specific segments of dna with the participation of d receptor interacting proteins (called drip). vitamin d is converted in the liver and kidney to calcitriol and ultimately acts through these receptors.Vitamin D3 24-Hydroxylase
a cytochrome p-450 enzyme that has specificity for cholecalciferol (vitamin d3). it hydroxylates the molecule at carbon position 24.Cholecalciferol
derivative of 7-dehydroxycholesterol formed by ultraviolet rays breaking of the c9-c10 bond. it differs from ergocalciferol in having a single bond between c22 and c23 and lacking a methyl group at c24.Dihydrotachysterol
a vitamin d that can be regarded as a reduction product of vitamin d2.Esculin
a derivative of coumarin with molecular formula c15h16o9.Niacinamide
an important compound functioning as a component of the coenzyme nad. its primary significance is in the prevention and/or cure of blacktongue and pellagra. most animals cannot manufacture this compound in amounts sufficient to prevent nutritional deficiency and it therefore must be supplemented through dietary intake.Pantothenic Acid
a butyryl-beta-alanine that can also be viewed as pantoic acid complexed with beta alanine. it is incorporated into coenzyme a and protects cells against peroxidative damage by increasing the level of glutathione.Pyridoxal Phosphate
this is the active form of vitamin b 6 serving as a coenzyme for synthesis of amino acids, neurotransmitters (serotonin, norepinephrine), sphingolipids, aminolevulinic acid. during transamination of amino acids, pyridoxal phosphate is transiently converted into pyridoxamine phosphate (pyridoxamine).Pyridoxal Kinase
an enzyme that catalyzes reversibly the phosphorylation of pyridoxal in the presence of atp with the formation of pyridoxal 5-phosphate and adp. pyridoxine, pyridoxamine and various derivatives can also act as acceptors. ec 2.7.1.35.Pyridoxaminephosphate Oxidase
an enzyme catalyzing the deamination of pyridoxaminephosphate to pyridoxal phosphate. it is a flavoprotein that also oxidizes pyridoxine-5-phosphate and pyridoxine. ec 1.4.3.5.Pyridoxic Acid
the catabolic product of most of vitamin b 6; (pyridoxine; pyridoxal; and pyridoxamine) which is excreted in the urine.Pyridoxine
the 4-methanol form of vitamin b 6 which is converted to pyridoxal phosphate which is a coenzyme for synthesis of amino acids, neurotransmitters (serotonin, norepinephrine), sphingolipids, aminolevulinic acid. although pyridoxine and vitamin b 6 are still frequently used as synonyms, especially by medical researchers, this practice is erroneous and sometimes misleading (ee snell; ann ny acad sci, vol 585 pg 1, 1990).Pyrithioxin
a neurotropic agent which reduces permeability of blood-brain barrier to phosphate. it has no vitamin b6 activity.Vitamin B 6 Deficiency
a nutritional condition produced by a deficiency of vitamin b 6 in the diet, characterized by dermatitis, glossitis, cheilosis, and stomatitis. marked deficiency causes irritability, weakness, depression, dizziness, peripheral neuropathy, and seizures. in infants and children typical manifestations are diarrhea, anemia, and seizures. deficiency can be caused by certain medications, such as isoniazid.Flavin Mononucleotide
a coenzyme for a number of oxidative enzymes including nadh dehydrogenase. it is the principal form in which riboflavin is found in cells and tissues.Riboflavin
nutritional factor found in milk, eggs, malted barley, liver, kidney, heart, and leafy vegetables. the richest natural source is yeast. it occurs in the free form only in the retina of the eye, in whey, and in urine; its principal forms in tissues and cells are as flavin mononucleotide and flavin-adenine dinucleotide.Riboflavin Deficiency
a dietary deficiency of riboflavin causing a syndrome chiefly marked by cheilitis, angular stomatitis, glossitis associated with a purplish red or magenta-colored tongue that may show fissures, corneal vascularization, dyssebacia, and anemia. (dorland, 27th ed)Riboflavin Synthase
an enzyme that catalyzes the formation of riboflavin from two molecules of 6,7-dimethyl-8-ribityllumazine, utilizing a four-carbon fragment from one molecule which is transferred to the second molecule. ec 2.5.1.9.Fursultiamin
compound used for therapy of thiamine deficiency. it has also been suggested for several non-deficiency disorders but has not yet proven useful.Maple Syrup Urine Disease
an autosomal recessive inherited disorder with multiple forms of phenotypic expression, caused by a defect in the oxidative decarboxylation of branched-chain amino acids (amino acids, branched-chain). these metabolites accumulate in body fluids and render a maple syrup odor. the disease is divided into classic, intermediate, intermittent, and thiamine responsive subtypes. the classic form presents in the first week of life with ketoacidosis, hypoglycemia, emesis, neonatal seizures, and hypertonia. the intermediate and intermittent forms present in childhood or later with acute episodes of ataxia and vomiting. (from adams et al., principles of neurology, 6th ed, p936)Thiamin Pyrophosphokinase
an enzyme that catalyzes the formation of thiamine pyrophosphate from atp and thiamine. ec 2.7.6.2.Thiamine
3-((4-amino-2-methyl-5-pyrimidinyl)methyl)-5-(2- hydroxyethyl)-4-methylthiazolium chloride.Thiamine Deficiency
a nutritional condition produced by a deficiency of thiamine in the diet, characterized by anorexia, irritability, and weight loss. later, patients experience weakness, peripheral neuropathy, headache, and tachycardia. in addition to being caused by a poor diet, thiamine deficiency in the united states most commonly occurs as a result of alcoholism, since ethanol interferes with thiamine absorption. in countries relying on polished rice as a dietary staple, beriberi prevalence is very high. (from cecil textbook of medicine, 19th ed, p1171)Thiamine Monophosphate
thiamine dihydrogen phosphate ester. the monophosphate ester of thiamine. synonyms: monophosphothiamine; vitamin b1 monophosphate.Thiamine Pyrophosphatase
an enzyme that hydrolyzes thiamine pyrophosphate to thiamine monophosphate plus inorganic phosphate. ec 3.6.1.-.Thiamine Pyrophosphate
the coenzyme form of vitamin b1 present in many animal tissues. it is a required intermediate in the pyruvate dehydrogenase complex and the ketoglutarate dehydrogenase complex.Thiamine Triphosphate
3-((4-amino-2-methyl-5-pyrimidinyl)methyl)-4-methyl-5-(4,6,8,8-tetrahydroxy-3,5,7-trioxa-4,6,8-triphosphaoct-1-yl)thiazolium hydroxide, inner salt, p,p',p''-trioxide. the triphosphate ester of thiamine. in leigh's disease, this compound is present in decreased amounts in the brain due to a metabolic block in its formation.Thiamin-Triphosphatase
an enzyme present in nerve tissue. it catalyzes reversibly the formation of thiamine diphosphate and orthophosphate from thiamine triphosphate. ec 3.6.1.28.
Table of Drugs and ChemicalsClinical
Substances in the Table of Drugs and Chemicals that reference this code family. Always confirm in the Tabular List before coding.
Patient EducationClinical
Medication Errors
Medicines treat infectious diseases, prevent problems from chronic diseases, and ease pain. But medicines can also cause harmful reactions if not used correctly. Errors can happen in the hospital, at the health care provider's office, at the pharmacy, or at home. You can help prevent errors by:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T45.2X6A to ICD-9-CMHistory
Code HistoryHistory
FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.
Questions About T45.2X6AOverview
Is T45.2X6A (Underdosing of vitamins) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report underdosing of vitamins, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T45.2X6A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for underdosing of vitamins, such as an emergency visit or first evaluation.
Can T45.2X6A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because underdosing of vitamins, initial encounter describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.
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.
