Type III procollagen peptide is a serum marker of collagen turnover and is used to assess hepatic fibrosis in patients on long-term Methotrexate.
PIIINP is the amino terminal peptide of type III procollagen, released from the precursor peptide during the synthesis and deposition of type III collagen. PIIINP in the serum can be derived from the synthesis of new type III collagen or from the degradation of existing type III collagen fibrils. There is evidence that serum PIIINP measurement is an effective non-invasive test for the detection and monitoring of Methotrexate-induced liver fibrosis and cirrhosis, and serial measurements may reduce the need for liver biopsy. Dermatology patients with repeated normal levels of PIIINP are very unlikely to have significant liver damage from fibrosis or cirrhosis. Conversely a high serum PIIINP or series of high values may indicate that a liver biopsy is required and in some cases, that Methotrexate should be withdrawn.
Note that PIIINP can be raised following bone fracture and also in rheumatology patients as it can be falsely elevated in inflammatory arthritis.
Consider liver biopsy in adult patients treated with Methotrexate for psoriasis:
Pre-treatment PIIINP > 8.0 g/L
PIIINP > 4.2 g/L in three samples over 12 months
PIIINP > 8.0 g/L in two consecutive samples
Consider withdrawal of Methotrexate:
PIIINP > 10 g/L in three samples over 12 months
The decision whether to perform liver biopsy, withdraw or continue treatment must also consider disease severity, patient age and alternative therapies. A rapid unusual fall or rise or a consistent downward or continuing upward trend in any marker should prompt caution and extra vigilance. [BSR/BHPR guideline for disease-modifying
anti-rheumatic drug (DMARD) therapy in consultation with the British Association of Dermatologists Rheumatology;Rheumatology 2008]
Serum (SST) sample is required.
Specialist Assay Laboratory