Leukemoid reaction

This code represents a reactive, non-neoplastic increase in white blood cells, particularly neutrophils, that mimics leukemia. It is a benign condition characterized by a peripheral leukocyte count typically exceeding 50,000/µL, often with the presence of immature granulocytes. This response is usually secondary to severe infection, inflammation, malignancy, or other significant physiological stress.

Assign this code when documentation clearly indicates a diagnosis of leukemoid reaction, distinguishing it from true leukemia. This diagnosis is typically supported by a complete blood count (CBC) showing marked leukocytosis with a left shift, and often a bone marrow biopsy ruling out a primary hematologic malignancy. Use this code as a secondary diagnosis when the underlying cause is known and coded separately.

• Always code the underlying condition causing the leukemoid reaction first, as this is a manifestation of another disease process.
• Differentiate carefully from true leukemia (C91-C95); leukemoid reaction is reactive, not neoplastic.
• Ensure documentation specifies "leukemoid reaction" and not just "leukocytosis," as simple leukocytosis has a different code.