D89.49

HCC Category Mapping

What This Code Means

Other types of mast cell activation disorders not specifically classified elsewhere, including rare or atypical presentations of mast cell dysfunction.

Coding Tips

• •Use this code only when the specific type of mast cell activation disorder does not fit other D89.4x codes
• •Include detailed documentation of the specific disorder in the medical record

Clinical Significance

This code captures other specified mast cell activation disorders that do not fit into the monoclonal, idiopathic, secondary, or hereditary alpha tryptasemia categories. It serves as a residual category for atypical or evolving presentations of mast cell activation where the clinician has identified a specific type that lacks its own unique ICD-10-CM code. These cases may require specialized immunology or allergy management.

Documentation Requirements

• ✓Documentation should describe the specific type of mast cell activation disorder that does not fit the established categories, including clinical presentation, laboratory findings (tryptase levels, other mediator measurements), and the rationale for classifying it outside the standard subtypes.
• ✓Workup results that exclude monoclonal, idiopathic, and secondary forms should be documented.

Commonly Confused Codes