Procollagen-3 N-Terminal Peptide (P3NP)
Methotrexate is a successful form of treatment for psoriasis and rheumatoid arthritis (RA). It has, however, been noted that prolonged exposure can result in irreversible hepatic fibrosis, the risk of which is idiopathic but associated with cumulative doses of more than 1.5g (usually encountered in psoriasis as lower doses are used in RA). Previously it was advised that a liver biopsy be considered after each cumulative 1.5g methotrexate. In 1996 it was shown that serum P3NP concentrations were predictive of the development of hepatic fibrosis. Continually raised P3NP concentrations were found to be associated with fibrosis in 78-100% of cases, but were only seen in 15-18% of subjects with a normal liver on biopsy. Current guidelines issued by the British Association of Dermatologists (2016) on the use of methotrexate in psoriasis suggest P3NP measurements be carried out annually and three monthly after a raised value. At Viapath, we use guideline-recommended radioimmunoassay.
In adults with psoriasis receiving methotrexate, P3NP results should be interpreted as follows:
- If P3NP is greater than 4.2 μg/L for the first time: repeat test in 3 months.
- If P3NP is raised:
> 8 μg/L on two occasions; or
> 4.2 μg/L but < 8.0 μg/L on three occasions within 12 months; or
> 10 μg/L on one occasion
results may indicate liver fibrosis - suggest onward referral for specialist advice.
The normal ranges for serum P3NP are as follows:
0-3 years 3.4 - 52.6 μg/L
4-9 years 3.4 - 12.1 μg/L
10-16 years 2.9 - 24.4 μg/L
17-18 years 2.0 - 7.0 μg/L
>19 years 1.2 - 4.2 ug/L
London SE5 9RS
London SE5 9RS
Last updated: 26/06/2018