What level of C-Reactive Protein (CRP) is significant in Pediatrics (Peds)?

From the Guidelines

In pediatrics, a C-reactive protein (CRP) level above 10 mg/dl is generally considered significant and indicative of inflammation or infection, as seen in patients with multisystem inflammatory syndrome in children (MIS-C) who often display elevations in inflammation markers, particularly CRP levels higher than 10 mg/dl or even 20 mg/dl 1. For most pediatric patients:

• CRP < 10 mg/dl: Normal range
• CRP 10-50 mg/dl: Mild elevation, suggestive of mild inflammation or viral infection
• CRP > 50 mg/dl: Moderate to severe elevation, often indicating bacterial infection or significant inflammation However, interpretation should always consider the clinical context. Some key points to remember:

1. Serial measurements are often more informative than a single value.
2. CRP levels typically rise within 4-6 hours of the onset of inflammation and peak at 48-72 hours.
3. CRP is non-specific and can be elevated in various conditions, including infections, autoimmune diseases, and tissue damage.
4. In neonates, the threshold for significance may be lower, with some experts considering levels above 5 mg/L as potentially concerning. CRP is useful because it's a sensitive marker of inflammation and infection, and its measurement is recommended as part of a tiered diagnostic approach for patients with possible MIS-C, along with other laboratory studies such as complete blood cell count, complete metabolic panel, erythrocyte sedimentation rate, and testing for SARS-CoV-2 1. The American Heart Association also suggests that CRP is a valuable tool in the diagnosis and management of Kawasaki disease, another condition that affects pediatric patients, and that CRP levels can be used to assess response to treatment with intravenous immunoglobulin (IVIG) 1. While other studies have suggested different thresholds for significance, such as 3.0 mg/L for high risk 1, the most recent and highest quality study suggests that a CRP level above 10 mg/dl is significant in pediatrics 1.

From the Research

C-Reactive Protein Levels in Pediatrics

• The level of C-Reactive Protein (CRP) that is significant in pediatrics can vary depending on the context and the specific condition being diagnosed or monitored 2, 3, 4, 5, 6.
• In the context of respiratory infections, a CRP level of 40 mg/l or higher may be indicative of bacterial infection, while levels below 20 mg/l may not rule out bacterial infection 2.
• In cases of suspected neonatal bacterial infection, a CRP level of less than 10 mg/l may indicate that antibiotic treatment can be safely discontinued 4.
• For pediatric appendicitis, higher CRP levels and Pediatric Appendicitis Scores (PAS) are associated with increased histologic inflammation of the appendix, and a combined PAS ≥ 8 and CRP level > 40 mg/l may be predictive of complicated appendicitis 5.
• In the diagnosis of bacterial gastroenteritis, CRP levels of 95 mg/l or higher may be suggestive of bacterial disease, with a sensitivity of 87% and a specificity of 91.7% for predicting culture-confirmed bacterial gastroenteritis 6.
• It is also important to note that low-level inflammation, as indicated by CRP values below 5-10 mg/l, can still affect biological parameters used to assess nutritional status, and a high-sensitivity CRP assay may be necessary to detect this low-level inflammation 3.