PIIINP (P3NP; Procollagen 3 N-terminal peptide)
Chemical Pathology
Notes
PIIINP is the amino terminal peptide of type III procollagen, released 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 for dermatology patients that serum PIIINP measurement is a useful 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.
Note that PIIINP can be raised following bone fracture and also in rheumatology patients as it can be falsely elevated in inflammatory arthritis and so is not recommended routinely in these patients.
This test is not useful in paediatric patients (<18 years of age) due to raised PIIINP levels associated with growth.
Sample requirements
For adults, 5 ml of blood taken into a narrow gold top tube (or rust top for the Acute Unit) sent immediately (less than 1 hour) to the laboratory.
Storage/transport
Do not store but send immediately to the laboratory (less than 1 hour).
Required information
Relevant clinical details including whether the sample is for pre-treatment investigations for psoriasis or if the patient is currently being treated with methotrexate for dermatological causes.
Turnaround times
The samples are sent to an external laboratory for analysis, with results expected back within 5 weeks.
Reference ranges
Adult ( ≥18 years) PIIINP reference range: 1.7 - 4.2 ug/L
Interpretation
Consider biopsy in adult psoriatics on Methotrexate if Pre-treatment > 8.0 ug/L, or three samples > 4.2ug/L in twelve month period, or two samples >8.0 ug/L consecutively. Consider withdrawing methotrexate if three samples > 10.0 ug/L in a twelve month period. Active erosive arthritis or fractures may raise PIIINP
Note that, the decision whether to perform liver biopsy, withdraw or continue treatment despite raised PIIINP must also take into account other factors such as patient age, disease severity, and the ease with which alternative therapies may be used in place of methotrexate.
Further information
British Association of Dermatology Guidelines
Page update 05/02/2025