Pyrrole Disorder can best be described as the abnormal synthesis and metabolism of the oxygen carrying molecule in your blood, called haemoglobin. All cells in your body produce waste or by-products and the by-product of haemoglobin is a metabolite called hydroxyhemopyrrolin-2-one (HPL) also known as Pyrrole. This metabolite was originally thought to be a Kryptopyrrole but further studies have proven this not the case.