P1NP: The Collagen Fragment Measured as a Marker of Bone Building

What it is

P1NP stands for procollagen type I N-terminal propeptide. Some papers write it PINP. It is not a drug or a supplement. It is a fragment the body makes, and a lab test measures it.

Type I collagen is the main protein of bone. Bone-building cells first make a longer version, called procollagen, with an extra piece at each end. Those end pieces are cut off as the collagen is made. P1NP is the piece from the front end, the N-terminal one. It passes into the blood, so its level reflects how much new collagen, and so how much new bone, is being laid down.

It is a large fragment of a protein, not a short peptide. The library's peptide vs. protein entry explains the difference. P1NP is listed here because it is the partner of C-telopeptide (CTX), a much smaller collagen fragment released when bone is broken down. The osteocalcin entry covers another marker of bone building.

Why it is the reference marker

In 2011 a joint working group of the International Osteoporosis Foundation (IOF) and the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reviewed studies from 2000 to 2010 (Osteoporos Int 2011, PMID 21184054). It recommended one formation marker, serum P1NP, and one resorption marker, serum CTX, as the reference markers for clinical studies. The stated reason was practical: if every study measures the same two markers with standardised assays, results can be compared.

In 2025 a larger group, now including the European society ESCEO, reviewed the literature from 2011 to May 2024 (Osteoporos Int 2025, PMID 40152990). It re-affirmed total P1NP in serum or plasma as a reference marker.

What the 2025 paper says it can and cannot do

Total and intact P1NP, and the kidney caveat

Labs use two kinds of assay, called total and intact P1NP. The 2025 paper singles out chronic kidney disease as the setting where the difference matters. It states that total P1NP may be raised because the kidneys retain it, which means a high reading may reflect kidney function and not bone building.

For that reason the paper limits its recommendation of total P1NP to people with normal kidney function. For osteoporosis linked to advanced kidney disease it names intact P1NP among the markers that "show the most promise", and recommends two other markers (bone alkaline phosphatase and TRACP5b) as the reference pair.

How samples are taken

The National Bone Health Alliance published sample-handling recommendations in 2017 (Osteoporos Int 2017, PMID 28631236). For P1NP they say collection conditions "are less critical", because it has "minimal circadian variability and is not affected by food intake". CTX is the opposite: it must be collected in the morning, fasted.

The same paper lists things that shift bone markers and cannot be controlled: age, sex, pregnancy, immobility, a recent fracture, other illnesses, osteoporosis drugs and other medicines. It asks that they be considered when a result is read. The library's teriparatide entry covers a drug whose label says it stimulates new bone formation.

What is not established

• No reference ranges are given here. They depend on the assay, the lab, age and sex.
• The 2025 paper says the markers are not yet part of fracture-risk algorithms.
• The 2017 paper states that bone-turnover markers "have not been widely adopted in clinical practice", mainly because results vary within a person and between labs.
• This entry rests on the abstracts of the three papers above. The full texts were not read for it, and the size of the P1NP fragment was not checked against a protein database.

Where it stands