PIIINP - aminoterminal propeptide of type III procollagen - is liberated into the circulation during soft tissue formation. Changes in PIIINP levels reflect the involvement and altered metabolism of type III collagen, which is common in many connective tissue disorders.

PIIINP can be used, for example, to assess and monitor fibrotic processes in liver diseases, thus avoiding the need for liver biopsies. It is also useful in monitoring growth hormone therapy in children with growth disorders. In cardiac disease, PIIINP gives prognostic information and reflects the healing process.