D89.43
BillableSecondary mast cell activation
HCC Category Mapping
V24HCC 47 — Disorders of Immunity
0.472ESRDHCC 47 — Disorders of Immunity
0.000RxHCCHCC 99 — Immunodeficiencies
0.000What This Code Means
Abnormal activation of mast cells that occurs as a result of another underlying disease, medication, or condition rather than as a primary disorder.
Coding Tips
- •Always identify and code the underlying cause when possible
- •This code should be used with a secondary diagnosis code for the causative condition
Clinical Significance
Secondary mast cell activation occurs when mast cell mediator release is triggered by an identifiable underlying condition such as chronic infections, autoimmune diseases, drug reactions, or other inflammatory disorders. Unlike idiopathic or monoclonal forms, the mast cell activation is a reactive process driven by an external stimulus. Treatment focuses on managing the underlying cause in addition to symptomatic anti-mediator therapy.
Documentation Requirements
- ✓Documentation must identify the specific underlying condition causing the secondary mast cell activation (chronic infection, autoimmune disease, allergic condition, medication reaction, or other trigger).
- ✓Evidence of mast cell activation (clinical symptoms, elevated mediator levels) should be recorded alongside the primary diagnosis.
- ✓Both the underlying cause and the secondary mast cell activation should be coded.
Code Also
- underlying etiology, if known
Commonly Confused Codes
D89.42 (Idiopathic mast cell activation syndrome) is used when no underlying cause is identified.D89.41 (Monoclonal mast cell activation syndrome) requires evidence of clonal mast cells.T78.40 (Allergy, unspecified) is less specific and does not capture the mast cell activation component.The code for the underlying causative condition should be assigned separately.