 Dr. Cameron informs House that Jeff's red blood count is continually dropping, revealing that his body is no longer able to produce red blood cells on its own.House becomes convinced that Jeff lied about a specific drug that could be the cause of all of his symptoms, erythropoietin (EPO), a hormone produced in the kidney that promotes the formation of red blood cells by the bone marrow.Adding more red blood cells increases the oxygen level in the blood, thus presumably causing all of Jeff's symptoms as he fails to produce red blood cells on his own.