The rationale for using the arithmetic difference between serum and urine is that by subtracting the urine S100B level from the serum S100B level, it might be possible to reduce the implication of the primary peak of S100B that only represents the injury caused by the impact, not the elevation of S100B caused by the actual intracranial hemorrhage. The gene discussed is S100B; the disease is intracranial hemorrhage.