Alkaline phosphatase is an enzyme that can be found in many of the body's tissues, but its highest concentration is inside bone and liver cells and in the bile ducts. It is a useful test to evaluate childhood liver and bone conditions, especially in conjunction with other tests, like liver functions tests and calcium and phosphate levels in the blood.
Alkaline phosphatase is abundant within liver cells. According to Lab Tests Online, any condition that affects the liver will cause the release of high quantities of alkaline phosphatase in the blood stream, which can then be picked up by a blood test. In particular, conditions that affect the bile ducts, the tiny tubes that carry bile from the liver into the intestine, cause marked elevation of alkaline phosphatase, as the cells that line the bile ducts have especially high levels of this enzyme. Conditions that affect bone growth or damage bone tissue can also cause elevations of the alkaline phosphatase level.
In children, the most common causes of an elevation in the alkaline phosphatase level include hepatitis, or an inflammation of the liver, usually caused by viruses; mononucleosis, which can cause hepatitis and painful swelling of the neck lymph nodes; overactivity of the parathyroid glands, the tiny glands that sit within the thyroid and which control bone metabolism; Paget's disease, a condition that causes excessive breakdown of bone; and rickets, caused by a deficiency of vitamin D in the diet.
According to the Children's Hospital Boston, children with liver conditions that cause elevation of the alkaline phosphatase level have jaundice, or a yellowish tinge of the skin; nausea and vomiting; easy bruising and bleeding; fatigue and weakness; and poor weight gain and appetite. Bone conditions with elevated alkaline phosphatase depend on the bones affected. They can cause localized bone pain, bending of the legs, and tingling or numbness in the extremities, and predispose the child to fractures even with only mild trauma.
The evaluation of a high alkaline phosphatase level in a child starts with the history of the illness and the symptoms. Alkaline phosphatase can be broken down into iso-enzymes that determine whether the elevation is coming from bone or from the liver. Other blood tests that can help in the diagnosis include liver function tests, including bilirubin, the substance that accumulates in the bloodstream if there is damage to the bile ducts and which causes jaundice; and levels of parathyroid hormone, calcium, and vitamin D. A liver or bone biopsy may be necessary to pinpoint the cause of the elevation of the alkaline phosphatase level.
The treatment for an elevation of the alkaline phosphatase level depends on the cause. Hepatitis due to viruses can be self-resolving, although children usually require symptomatic treatment with intravenous fluids and nausea-controlling medicines. Surgery may be necessary in cases of hyperparathyroidism, and in children with Paget's disease of the bone to fix fractures or bone misalignment. Medicines usually reserved for elderly patients with osteoporosis can also be used in children with Paget's.