What Does the Medical Acronym HI Stand For?
In the context of myelodysplastic syndromes (MDS) and hematologic disorders, HI stands for "Hematologic Improvement," which refers to measurable improvements in blood cell counts (erythroid, platelet, or neutrophil lineages) that persist for at least 2 months. 1
However, in a completely different medical context, HI also stands for "Hyperinsulinism" (or Congenital Hyperinsulinism), a disorder of inappropriate insulin secretion causing hypoglycemia. 2, 3, 4
Context Matters: Two Distinct Meanings
HI as Hematologic Improvement (MDS Context)
The International Working Group defines HI as a response criterion specifically for evaluating treatments in myelodysplastic syndromes that improve cytopenias without necessarily modifying disease course. 1
HI is categorized by affected cell lineage:
HI-E (Erythroid response): Major response requires hemoglobin increase >2 g/dL for patients with baseline <11 g/dL, or achieving transfusion independence in transfusion-dependent patients 1, 5
HI-P (Platelet response): Major response requires absolute platelet increase ≥30,000/mm³ for patients with baseline <100,000/mm³, or achieving platelet transfusion independence 1, 5
HI-N (Neutrophil response): Major response requires at least 100% increase in absolute neutrophil count (ANC) or absolute increase >500/mm³ (whichever is greater) for patients with baseline ANC <1500/mm³ 1, 5
All improvements must be sustained for at least 2 months in the absence of ongoing cytotoxic therapy and confirmed on at least 2 successive determinations at least 1 week apart. 1, 5
The ESMO guidelines clarify that HI responses are particularly adapted to treatments like growth factors that improve cytopenias but have no obvious effect on disease course, distinguishing them from complete remission (CR) or partial remission (PR). 1
HI as Hyperinsulinism (Endocrine Context)
In pediatric endocrinology, HI refers to congenital hyperinsulinism, a disorder of inappropriate insulin secretion by pancreatic β-cells causing recurrent hypoglycemia, with incidence of 1/50,000 live births (or 1/2,500 in consanguineous populations). 2, 3
This condition presents with:
- Recurrent hypoglycemic episodes requiring high glucose administration rates to maintain normoglycemia 3, 4
- Responsiveness to exogenous glucagon 3
- Risk of irreversible brain damage if untreated 2, 3, 6
The most severe forms are caused by recessive ABCC8 or KCNJ11 mutations affecting pancreatic potassium channels and are typically diazoxide-unresponsive. 2, 3, 4
Clinical Pitfall to Avoid
When encountering "HI" in medical documentation, always verify the clinical context—hematology/oncology versus endocrinology—as the meanings are completely unrelated and management implications are entirely different. The acronym appears in completely different specialties with no overlap in meaning or treatment approach.