Normal C-Reactive Protein Values in Neonates and Pediatric Patients
In neonates, normal CRP values are <10 mg/L (<95.2 nmol/L), while in older children and adults, normal values are typically <3 mg/L (<28.6 nmol/L). 1, 2, 3
Conversion to µmol/L
To convert CRP from mg/L to µmol/L, multiply by 9.52:
- Neonatal normal range: <10 mg/L = <95.2 µmol/L 1, 2
- Pediatric/adult normal range: <3 mg/L = <28.6 µmol/L 4, 1
Age-Specific Normal Values
Neonates (Birth to 28 Days)
- Cord blood CRP levels range from 10-370 ng/mL (0.01-0.37 mg/L or 0.095-3.5 µmol/L), with a median of 70 ng/mL (0.07 mg/L or 0.67 µmol/L). 3
- Two serial CRP measurements <10 mg/L (<95.2 µmol/L) obtained 24 hours apart are useful for excluding neonatal sepsis, with negative predictive values of 99.7%. 1, 2
- The initial CRP at presentation has poor sensitivity (35-39% for early-onset sepsis), but serial measurements dramatically improve diagnostic accuracy. 2
Pediatric Patients (Beyond Neonatal Period)
- Normal CRP in children is <3 mg/L (<28.6 µmol/L), consistent with adult reference ranges. 4, 1
- CRP values between 3-10 mg/L (28.6-95.2 µmol/L) suggest low-grade chronic inflammation. 4
- CRP >10 mg/L (>95.2 µmol/L) indicates acute inflammation or infection in pediatric patients. 5
Clinical Interpretation Thresholds in Pediatric Practice
Diagnostic Cut-offs for Specific Conditions
For acute appendicitis in children:
- CRP ≥10 mg/L (≥95.2 µmol/L) is a strong predictor, particularly in children <6 years old. 5
- CRP >40 mg/L (>380.8 µmol/L) was found in 58% of complicated appendicitis cases. 5
For Multisystem Inflammatory Syndrome in Children (MIS-C):
- Marked elevation is defined as CRP ≥10 mg/dL (≥100 mg/L or ≥952 µmol/L), which is a criterion for hospital admission. 5, 6
- Most MIS-C cases display CRP values >10-20 mg/dL (>100-200 mg/L or >952-1904 µmol/L). 5
For respiratory infections in children:
- CRP >40 mg/L (>380.8 µmol/L) has 88% specificity for bacterial versus viral infection, with a positive predictive value of 76%. 7
- CRP <40 mg/L (<380.8 µmol/L) does not rule out bacterial infection (sensitivity only 55%). 7
For influenza in children:
- CRP is unhelpful, with 55% of cases having values <10 mg/L (<95.2 µmol/L) and only 5% having values >80 mg/L (>761.6 µmol/L). 5
Critical Clinical Pitfalls
Never rely on a single CRP measurement to exclude serious bacterial infection in neonates. The initial CRP has inadequate sensitivity (35-64%), and antibiotic therapy should not be withheld based on normal initial values. 1, 2
In neonates with bloodstream infections, 25% have CRP ≤10 mg/L at sepsis onset. This occurs more frequently in extremely preterm infants, those with very low birth weight, early-onset sepsis, and coagulase-negative staphylococcal infections—yet 13% still progress to septic shock despite low CRP. 8
Serial CRP measurements are essential in neonates: A single normal value is insufficient, but two measurements 24 hours apart that remain <10 mg/L effectively exclude sepsis with 99.7% negative predictive value. 1, 2
The traditional 10 mg/L cut-off for "pathological" CRP is outdated and should not be used to automatically exclude participants or dismiss clinical concern. Many non-infectious factors (obesity, smoking, chronic inflammation) can elevate CRP above this threshold. 5, 4