thank you for your reply, with this in mind, that the process is sequential why not the same for which porphyria will have elevated PBG during acute attacks, but rather it is a bit of a 'hit and miss' which porphyria's have these elevated PBG levels.
In my readings so far it seems acceptable that PCT does not have elevated PBG levels during acute attacks and the reason for this can not be confirmed. Some literature put it down to the distance or position it is in the pathway, but if this is the case then why do we accept that HCP should still have elevated PBG levels during an attack but it is after PCT in the biosynthetic process.