2026 ICD-10-CM Diagnosis Code T39.1X5AAdverse effect of 4-Aminophenol derivatives, initial encounter

ICD-10-CM Codes›S00–T88›T36-T50›T39

ICD-10-CM T39.1X5A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T39.1X5A is a billable ICD-10-CM diagnosis code for adverse effect of 4-Aminophenol derivatives, 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 caused by acetaminophen. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Adverse effects of drugs and medicaments, initial encounter.

Code Identity

ICD-10-CM Code
T39.1X5A
Billable Status
Yes — Valid for Submission
Code Describes
Adverse effect of 4-Aminophenol derivatives, initial encounter
Short Description
Adverse effect of 4-Aminophenol derivatives, init encntr
Parent Code
T39.1X5
Adverse effect of 4-Aminophenol derivatives

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT36-T50Poisoning by, adverse effect of and underdosing of drugs, medicaments and biological substances
CategoryT39Poisoning by, adverse effect of and underdosing of nonopioid analgesics, antipyretics and antirheumatics
This CodeT39.1X5AAdverse effect of 4-Aminophenol derivatives, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T39.1X5A.

Unacceptable principal diagnosis
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.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Adverse reaction caused by acetaminophen
  • Adverse reaction to acetanilide
  • Adverse reaction to phenacetin
  • Para-aminophenol derivative 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 nonopioid analgesics, antipyretics and antirheumatics (T39). 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 INJ028
Adverse effects of drugs and medicaments, initial encounter
Default principal diagnosis: inpatient No · outpatient Yes

Clinical InformationClinical

  • Acetaminophen

    analgesic antipyretic derivative of acetanilide. it has weak anti-inflammatory properties and is used as a common analgesic, but may cause liver, blood cell, and kidney damage.

  • Arylsulfotransferase

    a sulfotransferase that catalyzes the sulfation of a phenol in the presence of 3'-phosphoadenylylsulfate as sulfate donor to yield an aryl sulfate and adenosine 3',5'-bisphosphate. a number of aromatic compounds can act as acceptors; however, organic hydroxylamines are not substrates. sulfate conjugation by this enzyme is a major pathway for the biotransformation of phenolic and catechol drugs as well as neurotransmitters. ec 2.8.2.1.

  • Cytochrome P-450 CYP1A2

    a cytochrome p450 enzyme subtype that has specificity for relatively planar heteroaromatic small molecules, such as caffeine and acetaminophen.

  • Phenacetin

    a phenylacetamide that was formerly used in analgesics but nephropathy and methemoglobinemia led to its withdrawal from the market. (from smith and reynard, textbook of pharmacology,1991, p431)

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.

SubstanceAccidentalSelf-harmAssaultUndeter­minedAdverse
Effect		Under­dosing
P-AcetamidophenolT39.1X1T39.1X2T39.1X3T39.1X4T39.1X5T39.1X6
AcetaminophenT39.1X1T39.1X2T39.1X3T39.1X4T39.1X5T39.1X6
AcetaminosalolT39.1X1T39.1X2T39.1X3T39.1X4T39.1X5T39.1X6
AcetanilideT39.1X1T39.1X2T39.1X3T39.1X4T39.1X5T39.1X6
AcetophenetedinT39.1X1T39.1X2T39.1X3T39.1X4T39.1X5T39.1X6
4-Aminophenol derivativesT39.1X1T39.1X2T39.1X3T39.1X4T39.1X5T39.1X6
Bromo-seltzerT39.1X1T39.1X2T39.1X3T39.1X4T39.1X5T39.1X6
ExalginT39.1X1T39.1X2T39.1X3T39.1X4T39.1X5T39.1X6
PanadolT39.1X1T39.1X2T39.1X3T39.1X4T39.1X5T39.1X6
Para-acetamidophenolT39.1X1T39.1X2T39.1X3T39.1X4T39.1X5T39.1X6
Para-aminophenol derivativesT39.1X1T39.1X2T39.1X3T39.1X4T39.1X5T39.1X6
ParacetamolT39.1X1T39.1X2T39.1X3T39.1X4T39.1X5T39.1X6
PhenacetinT39.1X1T39.1X2T39.1X3T39.1X4T39.1X5T39.1X6

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 T39.1X5A to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
995.29 Adv eff med/biol NEC/NOS
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.
ICD-9-CM
E935.3 Adv eff salicylates
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.

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 T39.1X5AOverview

Is T39.1X5A (Adverse effect of 4-Aminophenol derivatives) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report adverse effect of 4-Aminophenol derivatives, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in T39.1X5A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for adverse effect of 4-Aminophenol derivatives, such as an emergency visit or first evaluation.

What MS-DRG does T39.1X5A group to?

On inpatient claims, adverse effect of 4-Aminophenol derivatives, 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 T39.1X5A be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because adverse effect of 4-Aminophenol derivatives, 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 T39.1X5A?

Under the General Equivalence Mappings, adverse effect of 4-Aminophenol derivatives, initial encounter converts to ICD-9-CM 995.29 (adv eff med/biol NEC/NOS) and E935.3 (adv eff salicylates). 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.