Determination of Neutrophil Half-Life

To the Editor: The leukocyte kinetic studies of patients on alternate-day steroid therapy by Dale, Fauci and Wolff (N Engl J Med 291:1154–1158, 1974) must be questioned because the method that they chose for measuring neutrophil half-life is only valid for a steady-state situation. The authors started their studies three to four hours after a dose of prednisone. With such timing, a steady state definitely does not exist, as is evident from our observations that the absolute peripheral neutrophil count rises.