2026 ICD-10-CM Diagnosis Code T37.2X6AUnderdosing of antimalarials and drugs acting on other blood protozoa, initial encounter
T37.2X6A is a billable ICD-10-CM diagnosis code for underdosing of antimalarials and drugs acting on other blood protozoa, 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
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T37.2X6A.
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 other systemic anti-infectives and antiparasitics (T37). 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
Amodiaquine
a 4-aminoquinoline compound with anti-inflammatory properties.Chloroquine
the prototypical antimalarial agent with a mechanism that is not well understood. it has also been used to treat rheumatoid arthritis, systemic lupus erythematosus, and in the systemic therapy of amebic liver abscesses.Cinchona
a genus of rubiaceous south american trees that yields the toxic cinchona alkaloids from their bark; quinine; quinidine; chinconine, cinchonidine and others are used to treat malaria and cardiac arrhythmias.Cinchona Alkaloids
alkaloids extracted from various species of cinchona.Eflornithine
an inhibitor of ornithine decarboxylase, the rate limiting enzyme of the polyamine biosynthetic pathway.Mefloquine
a phospholipid-interacting antimalarial drug (antimalarials). it is very effective against plasmodium falciparum with very few side effects.Primaquine
an aminoquinoline that is given by mouth to produce a radical cure and prevent relapse of vivax and ovale malarias following treatment with a blood schizontocide. it has also been used to prevent transmission of falciparum malaria by those returning to areas where there is a potential for re-introduction of malaria. adverse effects include anemias and gi disturbances. (from martindale, the extra pharmacopeia, 30th ed, p404)Proguanil
a biguanide compound which metabolizes in the body to form cycloguanil, an anti-malaria agent.Pyrimethamine
one of the folic acid antagonists that is used as an antimalarial or with a sulfonamide to treat toxoplasmosis.Quinacrine
an acridine derivative formerly widely used as an antimalarial but superseded by chloroquine in recent years. it has also been used as an anthelmintic and in the treatment of giardiasis and malignant effusions. it is used in cell biological experiments as an inhibitor of phospholipase a2.Quinacrine Mustard
nitrogen mustard analog of quinacrine used primarily as a stain in the studies of chromosomes and chromatin. fluoresces by reaction with nucleic acids in chromosomes.Quinine
an alkaloid derived from the bark of the cinchona tree. it is used as an antimalarial drug, and is the active ingredient in extracts of the cinchona that have been used for that purpose since before 1633. quinine is also a mild antipyretic and analgesic and has been used in common cold preparations for that purpose. it was used commonly and as a bitter and flavoring agent, and is still useful for the treatment of babesiosis. quinine is also useful in some muscular disorders, especially nocturnal leg cramps and myotonia congenita, because of its direct effects on muscle membrane and sodium channels. the mechanisms of its antimalarial effects are not well understood.
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 T37.2X6A to ICD-9-CMHistory
Code HistoryHistory
Questions About T37.2X6AOverview
Is T37.2X6A a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report underdosing of antimalarials and drugs acting on other blood protozoa, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T37.2X6A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for underdosing of antimalarials and drugs acting on other blood protozoa, such as an emergency visit or first evaluation.
Can T37.2X6A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because underdosing of antimalarials and drugs acting on other blood protozoa, 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.
