What is ICD-10 code D89.44?

D89.44 is the ICD-10-CM diagnosis code for Hereditary alpha tryptasemia. A hereditary condition where individuals have elevated levels of tryptase (an enzyme released by mast cells), predisposing them to mast cell activation and allergic reactions. D89.44 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. D89.44 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. D89.44 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. D89.44 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for D89.44?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. D89.44 was a payment HCC under V24 (Disorders of Immunity) but the V28 recalibration removed it from the risk adjustment model. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting D89.44?

Requires documentation of elevated baseline tryptase levels and family history This is a genetic predisposition code; document any associated mast cell activation symptoms Because D89.44 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

D89.44: Hereditary alpha tryptasemia — ICD-10

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupD89.44Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism (D50-D89) / Certain disorders involving the immune mechanism (D80-D89)

D89.44

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Hereditary alpha tryptasemia

A hereditary condition where individuals have elevated levels of tryptase (an enzyme released by mast cells), predisposing them to mast cell activation and allergic reactions.

Buddy Insight

Hereditary alpha tryptasemia is a genetic condition caused by increased copy number of the TPSAB1 gene encoding alpha-tryptase, resulting in elevated baseline serum tryptase levels.

CMS-HCC V28

Not risk-adjusted for this model/period.

RAF 0

CMS-HCC V24

Mapped

HCC 47

Disorders of Immunity

RAF 0.472

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 47

Disorders of Immunity

RAF 0.0

RXHCC

Mapped

HCC 99

Immunodeficiencies

RAF 0.0

Code Trumping

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Code Book Path

Official

D89Other disorders involving the immune mechanism, not elsewhere classified

D89.4Mast cell activation syndrome and related disorders

D89.44Hereditary alpha tryptasemia

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for D89.44 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for D89.44 in this effective period.

Related Child Codes

Official

D89.40Mast cell activation, unspecified

D89.41Monoclonal mast cell activation syndrome

D89.42Idiopathic mast cell activation syndrome

D89.43Secondary mast cell activation

D89.49Other mast cell activation disorder

Includes

Official

ICD-10-CM does not list Includes notes for D89.44 in this effective period.

Excludes 1

Official

aggressive systemic mastocytosis (C96.21)
congenital cutaneous mastocytosis (Q82.2)
(non-congenital) cutaneous mastocytosis (D47.01)
(indolent) systemic mastocytosis (D47.02)
malignant mast cell neoplasm (C96.2-)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for D89.44 in this effective period.

Use Additional

Official

code, if applicable, for:
allergy status, other than to drugs and biological substances (Z91.0-)
personal history of anaphylaxis (Z87.892)

Code Also

Official

ICD-10-CM does not list Code Also instructions for D89.44 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation should include genetic testing confirming increased TPSAB1 gene copy number, baseline elevated serum tryptase levels, and associated clinical symptoms.

Family history of elevated tryptase or similar symptoms supports the diagnosis.

The provider should document whether the patient is symptomatic or the finding is incidental, and note any treatment with anti-mediator therapy.

MEAT Support

HCC Buddy guidance

Documentation should include genetic testing confirming increased TPSAB1 gene copy number, baseline elevated serum tryptase levels, and associated clinical symptoms.

Family history of elevated tryptase or similar symptoms supports the diagnosis.

The provider should document whether the patient is symptomatic or the finding is incidental, and note any treatment with anti-mediator therapy.

Audit Caution

HCC Buddy guidance

Do not assign this code for isolated elevated tryptase without genetic confirmation of TPSAB1 copy number gain.

Elevated tryptase alone can be seen in mastocytosis, renal insufficiency, and other conditions.

This is a genetic diagnosis, not a clinical diagnosis based on symptoms alone.

If the patient also has features meeting mast cell activation syndrome criteria, both conditions may be coded.

Common Mistakes

HCC Buddy guidance

D47.02 (Systemic mastocytosis) also causes elevated tryptase but is a neoplastic process with bone marrow involvement.

D89.41 (Monoclonal mast cell activation syndrome) requires clonal markers on mast cells rather than germline tryptase gene amplification.

D89.42 (Idiopathic mast cell activation syndrome) should be reconsidered if the patient has confirmed hereditary alpha tryptasemia as the underlying cause of their symptoms.

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is D89.44 an HCC code?

Yes. D89.44 maps to Disorders of Immunity under the V24 model but is not retained in V28.

HCC Category Mapping

V24HCC 47, Disorders of Immunity

0.472

ESRDHCC 47, Disorders of Immunity

0.000

RxHCCHCC 99, Immunodeficiencies

0.000

RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

MEAT Criteria for D89.44

For D89.44to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed D89.44 during that encounter, not just copy-forwarded from a problem list.

What This Code Means

D89.44 is the ICD-10-CM diagnosis code for hereditary alpha tryptasemia. A hereditary condition where individuals have elevated levels of tryptase (an enzyme released by mast cells), predisposing them to mast cell activation and allergic reactions. D89.44 sits in the ICD-10-CM chapter for diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism (d50-d89), within the section covering certain disorders involving the immune mechanism (d80-d89).

Under the older CMS-HCC V24 model, D89.44 maps to Disorders of Immunity (HCC 47) with a community, non-dual, aged base RAF weight of 0.472. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Requires documentation of elevated baseline tryptase levels and family history. Because D89.44 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for D89.44 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Requires documentation of elevated baseline tryptase levels and family history
•This is a genetic predisposition code; document any associated mast cell activation symptoms

Clinical Significance

Hereditary alpha tryptasemia is a genetic condition caused by increased copy number of the TPSAB1 gene encoding alpha-tryptase, resulting in elevated baseline serum tryptase levels. It affects approximately 5-6% of the general population and can present with mast cell activation-like symptoms including flushing, gastrointestinal dysmotility, connective tissue laxity, and dysautonomia. While often asymptomatic, symptomatic individuals may experience significant morbidity.

Documentation Requirements

✓Documentation should include genetic testing confirming increased TPSAB1 gene copy number, baseline elevated serum tryptase levels, and associated clinical symptoms.
✓Family history of elevated tryptase or similar symptoms supports the diagnosis.
✓The provider should document whether the patient is symptomatic or the finding is incidental, and note any treatment with anti-mediator therapy.

Use Additional Code

code, if applicable, for:
allergy status, other than to drugs and biological substances (Z91.0-)
personal history of anaphylaxis (Z87.892)

Commonly Confused Codes

•D47.02 (Systemic mastocytosis) also causes elevated tryptase but is a neoplastic process with bone marrow involvement.
•D89.41 (Monoclonal mast cell activation syndrome) requires clonal markers on mast cells rather than germline tryptase gene amplification.
•D89.42 (Idiopathic mast cell activation syndrome) should be reconsidered if the patient has confirmed hereditary alpha tryptasemia as the underlying cause of their symptoms.