Normal kidney size (children)

The normal size of kidneys in children follows a growth curve and is closely related to the age and size of the child. Ethnic differences have also been shown, which may be an important consideration when interpreting measurements against a reference range ⁴.

In infants normal averagemedian (normal range between the 2.5^th and the 97.5^th percentile in brackets) renal lengths on ultrasound are as follows ⁵:

• Neonates (<1 month old): 42.150.6 mm (normal range: 50.642.1-60.1 mm)

• 1 month old: 43.652.4 mm (normal range: 52.443.6-62.0 mm)

• 2 months old: 4554.2 mm (normal range: 5445.2-63.8 mm)

• 3 months old: 46.956.1 mm (normal range: 56.146.9-65.7 mm)

• 4 months old: 48.057.3 mm (normal range: 57.348.0-66.8 mm)

• 5 months old: 49.258.6 mm (normal range: 58.649.2-68.0 mm)

• 6 months old: 50.259.7 mm (normal range: 59.750.2-69.0 mm)

• 7 months old: 51.360.8 mm (normal range: 60.851.3-70.0 mm)

• 8 months old: 52.261.8 mm (normal range: 61.852.2-70.9 mm)

• 9 months old: 53.162.7 mm (normal range: 62.753.1-71.6 mm)

• 10 months old: 53.9 mm63.5mm (normal range: 63.553.9-72.2 mm)

• 11 months old: 54.664.2 mm (normal range: 64.254.6-72.8 mm)

In older children normal averagemedian (normal range between the 2.5^th and the 97.5^th percentile in brackets) sonographic renal lengths based on their age and sex are as follows ⁵:

• 1 year old

  ♂          65.2 mm (normal range: 54.6-76.8 mm)

  ♀           64.3 mm (normal range: 51.6-77.8 mm)

• 2 years old

  ♂          68.7 mm (normal range: 57.7-80.9 mm)

  ♀           68.4 mm (normal range: 55.4-82.4 mm)

• 3 years old         

  ♂          72.5 mm (normal range: 60.9-85.4 mm)

  ♀           71.7 mm (normal range: 58.4-86.2 mm)

• 4 years old         

  ♂          76.5 mm (normal range: 64.5-90 mm)

  ♀           75.8 mm (normal range: 62.3-90.8 mm)

• 5  years old        

  ♂          79.7 mm (normal range: 67.4-93.7 mm)

  ♀           78.9 mm (normal range: 65.3-94.1 mm)

• 6 years old         

  ♂          83 mm (normal range: 70.4-97.4 mm)

  ♀           81.6 mm (normal range: 67.9-97 mm)

• 7 years old         

  ♂          85.9 mm (normal range: 73-100.7 mm)

  ♀           84.9 mm (normal range: 71.2-100.5 mm)

• 8 years old         

  ♂          89.2 mm (normal range: 76-104.4 mm)

  ♀           87.8 mm (normal range: 74.1-103.5 mm)

• 9 years old         

  ♂          91.3 mm (normal range: 78-106.7 mm)

  ♀           90.8 mm (normal range: 77.1-106.7 mm)

• 10 years old      

  ♂          94.2 mm (normal range: 80.5-110.2 mm)

  ♀           93.1 mm (normal range: 79.4-109.1 mm)

• 11 years old      

  ♂          96.9 mm (normal range: 83.1-113.2 mm)

  ♀           95.9 mm (normal range: 80.9-113.8 mm)

• 12 years old      

  ♂          99.9 mm (normal range: 85.9-116.6 mm)

  ♀           97.9 mm (normal range: 84.5-113.8 mm)

• 13 years old      

  ♂          102.5 mm (normal range: 88.3-119.4 mm)

  ♀           100.1 mm (normal range: 86.8-116 mm)

• 14 years old      

  ♂          104.8 mm (normal range: 90.5-121.9 mm)

  ♀           101.8 mm (normal range: 88.6-117.6 mm)

• 15 years old      

  ♂          107.8 mm (normal range: 93.2-125.5 mm)

  ♀           103.5 mm (normal range: 90.5-119.1 mm)

• 16 years old      

  ♂          110.3 mm (normal range: 95.6-128.3 mm)

  ♀           105.2 mm (normal range: 92.4-120.7 mm)

• 17 years old      

  ♂          112.8 mm (normal range: 98-131 mm)

  ♀           107 mm (normal range: 94.6-122.1 mm)

• 18 years old      

  ♂          115.6 mm (normal range: 100.6-134 mm)

  ♀           108.3 mm (normal range: 95.9-123.4 mm)

The best predictor of renal length in children is height, regardless of sex ³. Limits of normal kidney length (millimetres) in children can be calculated using the following formulas ³:

• 2.5^th percentile: 0.4 × height [cm] + 20.4

• 50^th percentile: 0.5 x height [cm] + 28.2

• 97.5^th percentile: 0.5 × height [cm] + 34.8

Note: the left kidney is usually slightly longer than the right.