Procalcitonin Guidance in Catastrophic Antiphospholipid Syndrome (CAPS)

Understanding Procalcitonin Behavior

Shock states, including cardiogenic and hemorrhagic shock, can elevate procalcitonin independent of infection in CAPS patients, which is highly relevant since CAPS patients often present in shock 1
Drug hypersensitivity reactions can cause procalcitonin elevation, an important consideration given the multiple medications used in CAPS management 1
Procalcitonin levels <0.25 ng/mL have 96-98.6% negative predictive value for bacterial infections, particularly gram-negative infections, making this threshold useful for ruling out bacterial complications 2
Values >0.5 ng/mL indicate higher probability of bacterial infection, with progressively higher levels correlating with infection severity 1
Procalcitonin typically rises within 2-3 hours of infection onset, making it useful for early detection of bacterial complications in CAPS patients 1

Procalcitonin should never be used alone to make clinical decisions about initiating or withholding antibiotics, but must be integrated with clinical assessment, imaging, and other laboratory findings 1
The sensitivity for detecting bacterial infection ranges only from 38-91%, meaning normal levels cannot definitively exclude infection 1
When evaluating fever or clinical deterioration in CAPS, measure procalcitonin as part of comprehensive assessment, not in isolation 1
If procalcitonin is <0.25 ng/mL combined with low clinical suspicion, bacterial infection is unlikely, consider disease activity or non-bacterial causes 2
Serial measurements of procalcitonin provide more value than single readings for tracking response to therapy 1

Do not delay antibiotics in clinically unstable CAPS patients while awaiting procalcitonin results, as mortality risk is extremely high 1
C-reactive protein is NOT helpful for infection discrimination in CAPS, as it will be markedly elevated from the underlying inflammatory/thrombotic process itself 3