The following sections explain each blood test listed in the table in section “Values for healthy children.”

Hemoglobin (Hgb)

Red cells contain Hgb, the molecules that carry oxygen and carbon dioxide in the blood. Measuring Hgb gives doctors an exact picture of the ability of the child’s blood to carry oxygen. Children may have low Hgb levels at diagnosis and during the intensive parts of treatment; this is because both cancer and chemotherapy decrease the bone marrow’s ability to produce new red cells. Signs and symptoms of anemia—paleness, shortness of breath, fatigue—may occur if the Hgb gets very low.

Hematocrit (HCT)

The HCT is sometimes called the packed cell volume. The purpose of the HCT test is to determine the ratio of plasma (the clear liquid part of blood) to red cells in the blood. For this test, blood is drawn from a vein, a finger prick, or central catheter and is spun in a centrifuge to separate the red cells from the plasma. The HCT is the percentage of red cells in the blood. For example, if the child has a HCT of 30 percent, it means that 30 percent of the amount of blood drawn was red cells and the rest was plasma.

When a child is on chemotherapy, the bone marrow does not make many red cells and the HCT goes down. When the HCT is low, less oxygen is carried in the blood, so your child will have less energy. Your child may be given a transfusion of packed red cells if the HCT goes below 18 or 19 percent.

Red blood cell count (RBC)

Red blood cells are produced by the bone marrow continuously in healthy children and adults. These cells contain hemoglobin, which carries oxygen throughout the body. To determine the RBC, an automated electronic device is used to count the number of red cells in a blood sample.

White blood cell count (WBC)

The total WBC determines the body’s ability to fight infection. Some treatments for brain and spinal cord tumor tumors kill healthy white cells or decrease the ability of the bone marrow to make new white cells. To determine the WBC, an automated electronic device counts the number of white cells in a blood sample.

White blood cell differential

When a child has blood drawn for a complete blood count (CBC), one section of the lab report will state the total WBC and a “differential,” meaning that each type of white blood cell will be listed as a percentage of the total. For example, if the total WBC count is 1,500 mm³, the differential might appear as in the following table:

The differential is obtained by microscopic analysis of a blood sample on a slide.

Absolute neutrophil count (ANC)

The ANC (also called the absolute granulocyte count or AGC) is a measure of the body’s ability to withstand infection. Generally, an ANC above 1,000 means the child’s infection-fighting ability is near normal.

To calculate the ANC, add the percentages of neutrophils (both segmented and band) and multiply by the total WBC. Using the example above, the ANC is 49 percent + 1 percent = 50 percent, and 50 percent of 1,500 (.50 x 1,500) = 750, so the ANC is 750.

Platelet count

Platelets are needed to repair the body and stop bleeding by forming clots. Because platelets are produced by bone marrow, platelet counts decrease when a child is on chemotherapy. Signs of low platelet counts are bruises and bleeding from the gums or nose. When their platelets are low, children with a brain or spinal cord tumor should be watched carefully for symptoms of bleeding in the brain (such as sudden headache, seizures, or any other changes in level of consciousness). Platelet transfusions are sometimes given when the count is lower than 20,000 or when there is bleeding. Platelets are counted by passing a blood sample through an electronic device.

Alanine aminotransferase (ALT)

ALT is also called serum glutamic pyruvic transaminase (SGPT). When doctors talk about liver functions, they are usually referring to blood sample tests that measure liver damage. If chemotherapy is causing liver damage, the liver cells release an enzyme called ALT into the blood serum. ALT levels can go up into the hundreds, or even thousands, in some children on chemotherapy. Each institution and protocol has different points at which chemotherapy drug dosages are decreased or stopped to allow the child’s liver to recover.

Aspartate aminotransferase (AST)

AST is also called serum glutamic oxaloacetic transaminase (SGOT). AST is an enzyme present in high concentrations in tissues with high metabolic activity, such as the liver. Severely damaged or killed cells release AST into the blood. The amount of AST in the blood is directly related to the amount of tissue damage. Therefore, if your child’s liver is being damaged by chemotherapy, the AST count can rise into the thousands. Viral infections or reactions to an anesthetic can also cause an elevated AST.

Bilirubin

The liver converts hemoglobin released from damaged red cells into bilirubin. The liver then removes bilirubin from the blood and excretes it into bile, which is a fluid released into the small intestine to aid digestion. If too much bilirubin is present in the body, it causes a yellow color in the skin and whites of the eyes that is called jaundice.

The two types of bilirubin are indirect (also called unconjugated) and direct (also called conjugated). An increase in indirect bilirubin is seen when destruction of red cells has occurred, and an increase of direct bilirubin is seen when there is a dysfunction or blockage of the liver.

Blood urea nitrogen (BUN)

The BUN blood test is used to assess kidney function. It is also used to detect liver disease, dehydration, congestive heart failure, gastrointestinal bleeding, or shock. The test measures the amount of an end product of protein metabolism, called urea nitrogen, in the blood. For children with kidney or liver damage, BUN is often at abnormal levels.

Creatinine

Creatinine is a breakdown product of protein metabolism found in the urine and the blood. In children with brain or spinal cord tumors, creatinine is measured to assess kidney function. An elevated blood creatinine level is often seen in children with kidney insufficiency or failure.

Carbon dioxide (CO2)

The CO2 test measures the acidity of the blood. Low CO2 levels can be caused by chronic excessive breathing (hyperventilation). High CO2 levels in children with brain or spinal cord tumors indicate dysfunction in the brainstem, which controls breathing.

Chloride

Chloride helps the body maintain its normal balance of fluids. The most common chloride abnormality seen in children with brain or spinal cord tumors is a low chloride level caused by excessive sweating or fast breathing.

Glucose

The amount of glucose (sugar) in blood changes throughout the day, depending on when, what, and how much people eat, and whether or not they have exercised. A normal fasting (no food for 8 hours) blood glucose level is between 70 and 99 mg/dL. A normal blood sugar level 2 hours after eating is less than 140 mg/dL. Elevated glucose levels can occur in children with brain and spinal cord tumors who are taking steroids.

Potassium

Potassium is important for the proper functioning of the nerves and muscles, particularly the heartbeat. Too much or too little potassium increases the chance of irregular heartbeats. Potassium levels can be altered by chemotherapy or other treatments for children with brain or spinal cord tumors.

Sodium

The amount of sodium (salt) in the body is regulated by the brain, kidneys, and adrenal glands. Tumors in the pituitary, hypothalamus, or brainstem can cause high or low sodium levels. In addition to frequent blood tests for sodium levels, a careful record of urine output is necessary for children with abnormalities in sodium regulation. High blood sodium is associated with excessive urination, and low sodium levels result in low urine output.

Calcium and magnesium

Calcium and magnesium are minerals that can be compared to the spark plugs in your car—they spark the chemical reactions in your body needed to make it function properly. Calcium and magnesium also help to develop and maintain the strength of bones. In addition, magnesium is necessary for the development of muscle and for nerve conduction throughout the body. Many chemotherapy drugs given to children with brain or spinal cord tumors decrease the calcium and magnesium levels in the blood.