It was already known at this time that non-heme Protoporphyrin IX levels were elevated in these conditions, but prior investigators had used acidic extraction methods in their assays that converted ZPP to unbound Protoporphyrin IX.
Nesa época xa se sabía que os niveis de protoporfirina IX non hémica estaban elevados nesas condicións, pero investigacións previas utilizaran métodos de extracción que convertían a ZPP en protoporfirina IX libre.