What is the clinical utility of C-Reactive Protein (CRP) in the inpatient setting?

From the Guidelines

CRP (C-reactive protein) is a valuable inflammatory marker in the inpatient setting for monitoring acute inflammation, infection, and treatment response, particularly when used in conjunction with clinical evaluation and other diagnostic tools 1. Key uses of CRP in hospitalized patients include:

• Diagnosing and monitoring bacterial infections
• Assessing severity of inflammatory conditions
• Guiding antibiotic therapy decisions
• Predicting outcomes in sepsis and other critical illnesses
• Monitoring response to treatment for infections or inflammatory disorders CRP levels typically rise within 4-6 hours of an inflammatory stimulus and peak at 48-72 hours, with normal levels being <10 mg/L and levels >100 mg/L suggesting severe inflammation or infection 1. When using CRP:

• Order on admission and repeat every 24-48 hours to track trends
• Interpret in conjunction with clinical presentation and other lab tests
• Remember CRP is non-specific; elevations can occur in various inflammatory conditions The most recent guidelines suggest measuring CRP in addition to bedside clinical evaluation for critically ill patients with a new fever and no clear focus of infection, when the probability of bacterial infection is deemed low to intermediate 1. CRP is produced by the liver in response to pro-inflammatory cytokines, particularly IL-6, and its rapid response and correlation with inflammation severity make it valuable for real-time monitoring of a patient's inflammatory status during hospitalization 1. In comparison to procalcitonin (PCT), CRP has a sensitivity of 68-92% and a specificity of 40-67% as a marker of bacterial infection, whereas PCT has a sensitivity of 77% and a specificity of 79% for early diagnosis of sepsis in critically ill patients 1. However, the latest guidelines from 2023 suggest that either serum PCT or CRP can be used to rule out bacterial infection in critically ill patients with a new fever and no clear focus of infection, when the probability of bacterial infection is deemed low to intermediate 1.

From the Research

Clinical Utility of C-Reactive Protein (CRP) in the Inpatient Setting

• CRP is a useful marker of sepsis, and its levels can help evaluate the response to initial antimicrobial therapy in septic patients 2
• Changes in CRP levels over the first 48 hours of therapy can indicate ineffective initial antibiotic therapy, with a sensitivity of 77% and a specificity of 67% 2
• Serial CRP measurements may not be effective in monitoring disease course and planning hospital discharge in patients with blood stream infection or acute infection 3, 4

CRP Measurement in Specific Patient Populations

• In geriatric patients hospitalized for acute infection, CRP measurement at hospital admission can help detect acute infection and provide short-term prognostic information 4
• In patients with community-acquired infections, CRP levels can correlate with body temperature, but clinicobiological discrepancies can lead to therapeutic modifications 5

CRP as an Indicator of Sepsis Resolution

• Decreasing plasma CRP concentrations can be a good indicator of resolution of microbiologically-proven sepsis, with a sensitivity of 97%, specificity of 95%, and predictive value of 97% 6
• Daily measurement of CRP can be useful for monitoring the course of sepsis in ICU patients and may indicate successful treatment 6