Procalcitonin

Healthy adults have levels below 0.05 ug/L; laboratories print a variety of higher cut-offs, from 0.1 to 0.5 ug/L, depending on the reason the test was requested. The level is higher in the first days of life and in the general population with reduced kidney function.

Procalcitonin is a protein that many tissues release into the blood in response to bacterial infection, particularly when the infection has spread into the bloodstream. It rises more quickly than CRP, within a few hours, and rises much less with viral infections and with most non-infectious inflammation, which is what makes it useful.

Doctors request it almost entirely in hospital, in people who are unwell with a suspected infection, to help decide how likely a bacterial cause is and to follow the response to antibiotics. It is rarely requested in general practice.

• Bacterial infection, particularly when it has spread into the blood
• Major surgery, severe burns and severe injury, for a few days
• Severe shock of any cause
• Kidney disease, a little, because it is cleared more slowly
• Some rare thyroid and lung cancers
• The first two days of life

• Successful treatment of the infection, falling by about half each day
• Values below the detection limit are usual in healthy adults; there is no lower limit
• Some infections confined to one place, such as an abscess, raise it very little

• Major surgery or a large injury raises it for a few days without any infection
• Some medicines that stimulate the immune system raise it
• Methods and cut-offs differ between laboratories

No fasting needed. It is almost always requested in hospital and repeated daily; the direction of change over successive days matters more than one value.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.