O-Negative is a universal donor blood type.The minimum fuse time possible on O-Negative is 0.1 seconds. It may be wise to toss it before an engagement where the likelihood of sustaining damage is high, as the grenade can quickly whittle enemies health and return a short time later to heal the Vault Hunter. Your blood is in high demand Most hospitals ask for O Negative because it can be given to anyone in need Most of the time, O Negative blood is used for trauma. So what is O-negative blood O negative blood is a type of blood that can be transfused to any other blood type. A man races to find shelter in a roadside motel so he can take. Care should be taken not to rely on it too heavily for health regeneration, as the transfusion trails can be unreliable. With Steven McCarthy, Alyx Melone, Sandra Forsell. Its often used in medical emergencies when the blood type is not immediately known. The O-Negative is a high damage transfusion grenade, which leeches life from a target and returns health to the wielder. In most cases, O RhD negative blood (O-) can safely be given to anyone. Universal donor! – Increased damage, effect radius, and fuse time.