What is the normal specific gravity of urine in a child?

Normal Specific Gravity of Urine in Children

The normal specific gravity of urine in children is typically between 1.015 and 1.025 in the first morning void, with values less than 1.015 potentially indicating dilute urine that may be associated with conditions such as enuresis. 1

Understanding Urine Specific Gravity in Children

Urine specific gravity is an important clinical parameter that measures the kidney's ability to concentrate or dilute urine. It represents the ratio of the density of urine compared to that of water.

• First-morning urine specific gravity should be 1.025 or higher after overnight fluid restriction (12 hours), which serves as a useful screening measurement of renal concentrating ability 1
• Early-morning unconcentrated urine with specific gravity less than 1.015 has been proposed as a potential marker to distinguish between enuretic and non-enuretic children 1
• Some studies have found significantly lower morning urine specific gravity in children with enuresis compared to controls, though this finding has not been consistent across all research 1

Measurement Methods and Accuracy

Different methods exist for measuring urine specific gravity, each with varying degrees of accuracy:

• Hydrometry and refractometry show good correlation with urine osmolality (the gold standard) with correlation coefficients of r=0.86 and r=0.81, respectively 2
• Reagent strips (dipsticks) demonstrate poor correlation with osmolality (r=0.46) and are not considered reliable for accurate specific gravity measurement 2
• In newborns specifically, strip tests show very weak correlation with osmolality (r²=0.598) and should be used with caution 3

Clinical Significance in Pediatric Assessment

The measurement of urine specific gravity provides valuable clinical information:

• A specific gravity of 1.015 or lower in first morning urine has been associated with nocturnal enuresis in preschool children 4
• In a study of healthy preschool children aged 3-6 years, 40 of 47 children had a urine specific gravity greater than 1.020, and none of these children experienced bedwetting during the study period 4
• Children with specific gravity of 1.015 or lower were more likely to have a history of bedwetting 4

Factors Affecting Urine Specific Gravity

Several factors can influence urine specific gravity measurements:

• Urine composition (primarily urea, chloride, sodium, potassium, phosphate, uric acid, and sulfate) 5
• Hydration status and fluid intake patterns 6
• Time of day (typically highest in first morning void due to overnight fluid restriction) 5
• Presence of glucose, protein, or blood in urine can falsely elevate specific gravity readings 3

Clinical Application

When evaluating urine specific gravity in children:

• Use the first morning void for most accurate assessment of concentrating ability 5
• Consider that specific gravity values up to 1.015 generally indicate hypotonic urine with osmolality less than 211 mOsm/kg H₂O 3
• Be aware that reagent strip measurements may be less reliable, particularly with confounding variables such as urine pH ≥6.5, glucosuria, proteinuria, or hematuria 3
• For clinical and field settings where osmolality measurement isn't practical, a USG ≥1.013 correlates with urine osmolality >500 mOsm/kg with very high accuracy 6

Pitfalls and Caveats

• Different measurement methods yield different results - refractometry typically gives higher values than hydrometry 2
• Always use the same method for follow-up measurements to ensure consistency 2
• In newborns, strip tests for specific gravity have limited clinical usefulness and should only be considered reliable for low specific gravity values (≤1.015) 3
• Interpretation should always consider clinical context, including hydration status, medication use, and underlying conditions 5