PIIINP - aminoterminal propeptide of type III procollagen - is released into the bloodstream during soft tissue formation. Changes in PIIINP level reflect the involvement and altered metabolism of type III collagen, a feature of many connective tissue disorders.

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