Blood sugar is the amount of glucose in the bloodstream. It is crucial for normal operation of the body systems. For newborns it is essential for normal growth, activity and development.
Glucose is an energy source found in carbohydrates. Upon ingestion, it can be used as an immediate source of fuel for the body. Whatever is not immediately needed, can be stored in the muscles and liver as a stored energy source. Any excess above that is stored as fat. The normal values change with age, typically lower in infants and higher in children and adults.
Glucose is the main source of fuel for the brain, which is especially important for infants and children. During pregnancy, glucose is passed from the mother to the fetus through the placenta and umbilical cord. Some of that is stored in the placenta, and later in the fetal liver, heart, and muscles. These stores are important for supplying the baby's brain with the necessary glucose during delivery, and for nutrition after the baby is born. Most babies don't feed well the first few days after delivery, so the stored glucose is essential during that time. Once they are on a normal feeding schedule, breast milk or formula serves as the source of glucose for infants. As the babies get older and transition to tradtional food sources, they get their glucose from carbohydrate-based foods.
For healthy, full-term babies, normal glucose values are between 40 and 150 mg/dL. For premature infants, the normal range is between 30 and 150 mg/dL.
Hypoglycemia is when blood glucose values fall below the normal range. It can be acute or chronic. In infants and newborns it is often corrected with supplemental feedings. Problems arise when low blood glucose goes on for long periods of time, which can lead to brain damage. Hyperglycemia is when blood glucose values fall above the normal range.
There are multiple blood tests that are used to measure blood glucose. If your infant needs to be evaluated, a heel stick test is most often the way to obtain a blood sample for testing. The test will typically be repeated only if the values continue to fall in the abnormal ranges.