2026 ICD-10-CM Diagnosis Code T45.3X5AAdverse effect of enzymes, initial encounter
T45.3X5A is a billable ICD-10-CM diagnosis code for adverse effect of enzymes, 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. The code is not accepted as a principal diagnosis by the Medicare Code Editor. Coders also document this condition as adverse reaction to enzymes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Adverse effects of drugs and medicaments, initial encounter.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T45.3X5A.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Adverse reaction to enzymes
- Bromelains adverse reaction
- Chymotrypsin adverse reaction
- Deoxyribonuclease adverse reaction
- Hyaluronidase adverse reaction
Coding GuidelinesGuidance
When coding an adverse effect of a drug that has been correctly prescribed and properly administered, assign the appropriate code for the nature of the adverse effect followed by the appropriate code for the adverse effect of the drug.
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.
Clinical InformationClinical
Bromelains
protein-digesting and milk-clotting enzymes found in pineapple fruit juice and stem tissue. enzymes from the two sources are distinguished as fruit bromelain and stem bromelain. this enzyme was formerly listed as ec 3.4.22.4.Acatalasia
a rare autosomal recessive disorder resulting from the absence of catalase activity. though usually asymptomatic, a syndrome of oral ulcerations and gangrene may be present.Catalase
an oxidoreductase that catalyzes the conversion of hydrogen peroxide to water and oxygen. it is present in many animal cells. a deficiency of this enzyme results in acatalasia.Chymopapain
a cysteine endopeptidase isolated from papaya latex. preferential cleavage at glutamic and aspartic acid residues. ec 3.4.22.6.Chymases
a family of neutral serine proteases with chymotrypsin-like activity. chymases are primarily found in the secretory granules of mast cells and are released during mast cell degranulation.Chymotrypsin
a serine endopeptidase secreted by the pancreas as its zymogen, chymotrypsinogen and carried in the pancreatic juice to the duodenum where it is activated by trypsin. it selectively cleaves aromatic amino acids on the carboxyl side.Chymotrypsinogen
a serine endopeptidase secreted by the pancreas as its zymogen, chymotrypsinogen and carried in the pancreatic juice to the duodenum where it is activated by trypsin. it selectively cleaves aromatic amino acids on the carboxyl side.Coronavirus 3C Proteases
3c proteases that occur in species of coronaviridae.Penicillinase
a beta-lactamase preferentially cleaving penicillins. (dorland, 28th ed) ec 3.5.2.-.Pronase
a proteolytic enzyme obtained from streptomyces griseus.alpha 1-Antitrypsin
plasma glycoprotein member of the serpin superfamily which inhibits trypsin; neutrophil elastase; and other proteolytic enzymes.Aprotinin
a single-chain polypeptide derived from bovine tissues consisting of 58 amino-acid residues. it is an inhibitor of proteolytic enzymes including chymotrypsin; kallikrein; plasmin; and trypsin. it is used in the treatment of hemorrhage associated with raised plasma concentrations of plasmin. it is also used to reduce blood loss and transfusion requirements in patients at high risk of major blood loss during and following open heart surgery with extracorporeal circulation. (reynolds jef(ed): martindale: the extra pharmacopoeia (electronic version). micromedex, inc, englewood, co, 1995)Receptor, PAR-2
a g-protein-coupled, proteinase-activated receptor that is expressed in a variety of tissues including endothelium; leukocytes; and the gastrointestinal tract. the receptor is activated by trypsin, which cleaves off the n-terminal peptide from the receptor. the new n-terminal peptide is a cryptic ligand for the receptor. the uncleaved receptor can also be activated by the n-terminal peptide present on the activated thrombin receptor and by small synthetic peptides that contain the unmasked n-terminal sequence.Trypsin
a serine endopeptidase that is formed from trypsinogen in the pancreas. it is converted into its active form by enteropeptidase in the small intestine. it catalyzes hydrolysis of the carboxyl group of either arginine or lysine. ec 3.4.21.4.Trypsin Inhibitor, Bowman-Birk Soybean
a low-molecular-weight protein (minimum molecular weight 8000) which has the ability to inhibit trypsin as well as chymotrypsin at independent binding sites. it is characterized by a high cystine content and the absence of glycine.Trypsin Inhibitor, Kazal Pancreatic
a secreted kazal motif-containing serine peptidase inhibitor that inhibits trypsin. it is a protein composed of 56 amino acid residues and is different in amino acid composition and physiological activity from the kunitz bovine pancreatic trypsin inhibitor (aprotinin). it protects against the trypsin-mediated premature activation of enzyme precursors in the pancreas. mutations in the spink1 gene are associated with chronic pancreatitis.Trypsin Inhibitor, Kunitz Soybean
a high-molecular-weight protein (approximately 22,500) containing 198 amino acid residues. it is a strong inhibitor of trypsin and human plasmin.Trypsin Inhibitors
serine proteinase inhibitors which inhibit trypsin. they may be endogenous or exogenous compounds.Trypsinogen
the inactive proenzyme of trypsin secreted by the pancreas, activated in the duodenum via cleavage by enteropeptidase. (stedman, 25th ed)
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
Drug Reactions
Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions, such as drug interactions, side effects, and allergies.
The full article covers:
- What is a drug interaction?
- What are side effects?
- What are drug allergies?
- How can I stay safe when taking medicines?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T45.3X5A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T45.3X5AOverview
Is T45.3X5A (Adverse effect of enzymes) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report adverse effect of enzymes, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T45.3X5A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for adverse effect of enzymes, such as an emergency visit or first evaluation.
What MS-DRG does T45.3X5A group to?
On inpatient claims, adverse effect of enzymes, initial encounter maps to MS-DRG 917, 918, with relative weights from 0.8571 to 1.5684 depending on complications. Higher weights mean higher Medicare reimbursement.
Can T45.3X5A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because adverse effect of enzymes, initial encounter describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.
What is the ICD-9 equivalent of T45.3X5A?
Under the General Equivalence Mappings, adverse effect of enzymes, initial encounter converts to ICD-9-CM 995.29 (adv eff med/biol NEC/NOS) and E933.4 (adv eff enzymes 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.
