Procalcitonin

• Used to differentiate bacterial from viral infection
• Mostly for pneumonia
• Also elevated in fungus like Pneumocystis, Candida[1]

Limitations/Caveats

Like any test, procalcitonin has some limitations. False positive and false negatives occur.  Procalcitonin is more specific for bacterial infections than other inflammatory markers, such as white blood cell count, erythrocyte sedimentation rate, and C-reactive protein. However, false positives can still occur. Major stressors that cause systemic inflammation can elevated procalcitonin: [1]

• severe trauma
• cardiac arrest or circulatory shock
• surgery
• burns
• pancreatitis
• intracranial hemorrhage 

Procalcitonin can also be elevated [1]

• in  immediate postnatal period
• after receipt of immunomodulatory agents (such as T cell antibodies, alemtuzumab, interleukin-2, and granulocyte transfusions)
• with severe liver disease
• with certain neoplasms including medullary thyroid cancer
• other neuroendocrine tumors
• Certain autoimmune diseases
• Kawasaki disease
• this does not appear to be the case with most immune disorders (eg, rheumatoid arthritis or systemic lupus erythematosus)

 Other infectious nonbacterial etiologies that increase procalcitonin (though levels appear to be lower in these infections when compared with bacterial infections )  include [1]

• malaria 
• invasive Candida infections
• Other pulmonary mold infections, including aspergillosis, mucormycosis, and coccidioidomycosis can cause low-level elevations

Other conditions affect procalcitonin

Chronic kidney disease

Persons with chronic kidney disease (CKD) have higher baseline levels of procalcitonin, believed to be due to higher levels of circulating inflammatory cytokines. In one study, the average procalcitonin level in healthy persons with CKD prior to starting renal replacement was 1.82 ± 0.39 ng/mL. Levels drop with renal replacement therapy. Average levels in patients with CKD receiving hemodialysis range from 0.26 ng/ mL to 1.0 ng/mL prior to dialysis sessions. After dialysis, levels decline by 20 to 80 percent, varying with the mode of dialysis used. Despite higher baseline levels, procalcitonin does rise in the setting of infection in patients with CKD. However, the rate of rise may be slower than in healthy patients. Elimination is marginally prolonged in patients with CKD, with a mean half-life of 28.9 hours in healthy patients compared with 33 hours in patients with creatine clearance <30 mL/minute.[1]

Some experts suggest that higher procalcitonin thresholds be used for patients with renal dysfunction Others sugges.t that single procalcitonin levels are unreliable in patients with CKD and propose that trends in procalcitonin levels have greater predictive value. Additional studies are needed to determine how to best use procalcitonin in this population. [1]

Caveat

"Use of procalcitonin algorithms should never override clinical judgment. In most trials, algorithms were often overruled by clinical judgment, underscoring the fact that the assay should be used as an adjunct to clinical judgment and not a replacement." [1]


[1] C Rhee, M Mansour. Procalcitonin use in lower respiratory tract infections Uptodate