D89.42

Idiopathic mast cell activation syndrome

Risk-adjusting (HCC)Billable code

HCC risk adjustment mapping

CMS-HCC ESRD V24

HCC47

Disorders of Immunity

RxHCC V08

RXHCC99

Immune Disorders

Coding notes

Excludes 1 never coded together · Excludes 2 may co-exist

Inherited from D89.4Mast cell activation syndrome and related disorders
Excludes 1

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-) malignant mastocytoma (C96.29) mast cell leukemia (C94.3-) mast cell sarcoma (C96.22) mastocytoma NOS (D47.09) other mast cell neoplasms of uncertain behavior (D47.09) systemic mastocytosis associated with a clonal hematologic non-mast cell lineage disease (SM-AHNMD) (D47.02)

Inherited from D89Oth disorders involving the immune mechanism, NEC
Excludes 1

hyperglobulinemia NOS (R77.1) monoclonal gammopathy (of undetermined significance) (D47.2)

Excludes 2

transplant failure and rejection (T86.-)

Inherited from D80-D89Certain disorders involving the immune mechanism
Includes

defects in the complement system immunodeficiency disorders, except human immunodeficiency virus [HIV] disease sarcoidosis

Excludes 1

autoimmune disease (systemic) NOS (M35.9) functional disorders of polymorphonuclear neutrophils (D71-) human immunodeficiency virus [HIV] disease (B20)

Inherited from chapter 3Diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism
Excludes 2

autoimmune disease (systemic) NOS (M35.9) certain conditions originating in the perinatal period (P00-P96) complications of pregnancy, childbirth and the puerperium (O00-O9A) congenital malformations, deformations and chromosomal abnormalities (Q00-Q99) endocrine, nutritional and metabolic diseases (E00-E88) human immunodeficiency virus [HIV] disease (B20) injury, poisoning and certain other consequences of external causes (S00-T88) neoplasms (C00-D49) symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

Official Guidelines for D89.42

FY 2026 ›

Find D89.42 in the alphabetic index

1 index path leads to this code