Is a creatinine of 0.23 mg/dL and blood urea nitrogen (BUN) of 5 mg/dL normal for a 10‑month‑old infant?

Creatinine and BUN Values in a 10-Month-Old Infant

A creatinine of 0.23 mg/dL and BUN of 5 mg/dL are both normal and expected values for a 10-month-old infant. These values reflect appropriate kidney function for this age group.

Normal Pediatric Reference Ranges

Creatinine Interpretation

• Infants and young children have significantly lower creatinine values than older children and adults due to lower muscle mass and ongoing renal maturation 1.
• In the first year of life, plasma creatinine typically ranges from 0.2-0.4 mg/dL (approximately 18-35 μmol/L) 2.
• The reported value of 0.23 mg/dL falls well within the normal range for a 10-month-old 2.
• After 2 years of age, renal growth results in GFR equivalent to adults when adjusted for body surface area, but infants under 2 years have lower baseline values 1.

BUN Interpretation

• BUN of 5 mg/dL is at the lower end of normal but not pathological in infants 3, 2.
• Very low birthweight and preterm infants commonly demonstrate plasma urea levels that stabilize to very low levels (less than 2 mmol/L or approximately 5.6 mg/dL) after the first two weeks of life 3.
• In term infants at 10 months, BUN values between 5-18 mg/dL are generally acceptable 2.
• Plasma urea may be insensitive to changes in renal function in the post-perinatal period and can be influenced by protein intake, hydration status, and metabolic factors 3.

Important Clinical Caveats

Assay Method Matters

• Enzymatic creatinine assays should be used preferentially in pediatric populations 1.
• Jaffe-based methods have poor specificity at the low creatinine values encountered in children, with higher relative contribution of non-creatinine chromogens 1.
• Laboratories must ensure quality control processes include the lowest end of expected values for infants 1.

Context-Dependent Interpretation

• These values must be interpreted in clinical context - a well-appearing, adequately hydrated infant with normal urine output requires no intervention 1.
• If there are concerns about renal function, calculate estimated GFR using the Bedside Schwartz equation (though validation in children under 1 year is limited) 1.
• The revised Schwartz formula: GFR (ml/min per 1.73 m²) = 0.413 × (height in cm) / Creatinine (mg/dL) 1.

When to Investigate Further

• Serial measurements showing rising creatinine or BUN warrant evaluation 1.
• Consider underlying pathology if accompanied by oliguria, edema, hypertension, or failure to thrive 1.
• Extremely low BUN (< 2-3 mg/dL) may reflect inadequate protein intake rather than renal pathology 3.