Procollagen III N-peptide
Procollagen, PIIINP, P3NP
Monitoring for hepatic fibrosis, particularly in patients
receiving methotrexate treatment who should be checked at three to
six month intervals.
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 on the use of methotrexate in
psoriasis suggest P3NP measurements be carried out annually and
three monthly after a raised value.
Request on ICE
Analysed by referral laboratory if specific criteria met.
Patient on methotrexate therapy
Two to three weeks
Serum in Gold Top (SST)
Causes for Rejection
- Unlabelled sample
- Prolonged delay in reaching the laboratory
- Sample in SST tube
- Assay performed within the previous three months
Adult (20 - 65 years) < 4.2 µg/L
Levels are higher levels in young people due to growth
PIIINP is a sensitive indicator of hepatic fibrosis, but may be
raised in other conditions, particularly active connective tissue
A liver biopsy should be considered if:
- there are three P3NP levels above 4.2 ug/L or
- two levels above 8.0 ug/L over a 12 month period.
- A liver biopsy should also be considered if the pre-treatment
level is above 8.0 ug/L.
Consider withdrawing methotrexate if 3 samples > 10.0 μg/L in
a 12 month period