Can Anti-Thymocyte Globulin (ATG) increase the white blood cell count?

Anti-Thymocyte Globulin (ATG) and White Blood Cell Count Effects

Yes, Anti-Thymocyte Globulin (ATG) can cause leukocytosis (increased white blood cell count) as an adverse effect. This is documented in clinical guidelines for its use in transplantation and autoimmune conditions 1.

Mechanism and Evidence

• ATG is a polyclonal antibody preparation that targets T lymphocytes and is used in various clinical settings including transplantation and treatment of bone marrow failure syndromes 1, 2
• According to the American Heart Association guidelines, leukocytosis is listed as a known adverse event of corticosteroids, which are often used alongside ATG in treatment protocols 1
• ATG itself can cause various hematological effects, with rabbit ATG (thymoglobulin) specifically associated with leukopenia and thrombocytopenia as common adverse events 1
• However, paradoxically, during initial administration, ATG can cause a transient increase in white blood cell count before potentially causing leukopenia with continued use 3

Clinical Considerations

• The effect on white blood cell count may vary depending on:

  • The type of ATG used (rabbit vs. equine preparations) 4
  • The dosing regimen (typical doses range from 0.75-1.5 mg/kg IV daily for rabbit ATG or 10-15 mg/kg daily for equine ATG) 1
  • The clinical context (transplantation, bone marrow failure, autoimmune conditions) 2

• In transplantation protocols, ATG is commonly included in conditioning regimens:

  • For unrelated donor, cord blood, or haploidentical transplants, ATG is typically dosed at 10 mg/kg or ATG-F at 40 mg/kg 1
  • These protocols may include monitoring for hematologic effects 1

Important Monitoring Considerations

• Regular complete blood count monitoring is essential during ATG therapy 1
• White blood cell count fluctuations may occur throughout the treatment course:
  • Initial increase possible (leukocytosis)
  • Later decrease (leukopenia) with continued treatment 1, 3
• Other common adverse effects to monitor include:
  • Gastrointestinal symptoms (diarrhea, abdominal pain, nausea, vomiting)
  • Myalgias, headache, fever
  • Increased risk of infections (viral, fungal, bacterial)
  • Increased risk of post-transplant lymphoproliferative disorder (PTLD) 1

Clinical Applications

• In myelodysplastic syndromes (MDS), ATG is used as immunosuppressive therapy, particularly in patients with:

  • Hypoplastic bone marrow
  • HLA-DR15 positivity
  • Normal cytogenetics
  • Low-risk disease 1

• For aplastic anemia, ATG-based immunosuppressive therapy is a standard approach, with horse ATG showing better response rates than rabbit ATG 2, 4

• In both conditions, monitoring of blood counts is essential as ATG can affect all blood cell lines, including white blood cells 1, 2

Practical Recommendations

• When administering ATG, anticipate possible white blood cell count fluctuations and monitor complete blood counts regularly 1
• Be aware that initial leukocytosis may occur before potential leukopenia develops 3
• Consider prophylactic measures against infections if prolonged leukopenia develops 1
• The specific effect on white blood cell count may vary between patients and should be monitored individually 2