On day 2 of life, a 25-week gestation infant weighs 0.6 kg and has 45 mL of urine output in 24 hours. How many mL/kg/hour is the urine output?

• A. 2.0
• B. 3.125
• C. 3.75
• D. 4.2

Answer: (B)

The key idea is to express urine production as a rate per kilogram per hour. To get mL/kg/hour, take the total urine in mL and divide by the time in hours and by the baby’s weight in kilograms.

Compute: 45 mL over 24 hours for a baby weighing 0.6 kg means

mL/kg/hour = 45 ÷ (0.6 × 24) = 45 ÷ 14.4 = 3.125 mL/kg/hour.

This rate shows how much urine is produced per kilogram of body weight each hour, which helps assess renal perfusion and fluid status in a very premature infant.