Like most parents, you’ve guided and encouraged your child in her accomplishments. You held her hand as she took her first steps, and you beamed with pride when she recited her ABCs. But when your child stepped into the world of juvenile arthritis and its management, you may have felt as if you were the one who needed hand-holding. It can seem there is a whole new alphabet to learn – when your child’s doctor tells you he is ordering a CBC, an ESR or a UA, that your child has a positive ANA or negative RF, or that she’ll need regular LFTs.
Whether your child is just beginning the diagnostic process or is well into the management of arthritis, laboratory tests – which doctors often refer to by names that sound like secret code – are a part of life. Tests on even a small sample of blood or other bodily fluid can give the doctor an important glimpse into what’s going on throughout your child’s body, says Ilona Szer, MD, director of pediatric rheumatology at the Children’s Hospital of San Diego. Your doctor can use lab tests to rule out other conditions, determine the extent of disease or monitor the activity of the disease or the effects – both good and bad – of the drugs used to treat it.
To help you crack the code and make sense of the tests your child’s doctor orders, Dr. Szer identifies some of the most common tests prescribed by pediatric rheumatologists and provide explanations of the tests, their limitations, and why doctors use them.
CBC (Complete Blood Count)
What it is: A measure of three types of cells that are present in the blood – red cells (RBCs), which carry oxygen; white blood cells (WBCs), which fight infection; and platelets, which make the blood clot.
Why doctors order it: Cell counts can provide clues to your child’s condition. For example, white cell counts are very high in systemic juvenile rheumatoid arthritis (JRA) and low in lupus; platelets may be very low in lupus and very high in systemic JRA; anemia (low red blood cells) is almost always present in a child with systemic JRA. Some of the medications used to treat arthritis may cause gastric bleeding, and the RBC count might fall as a result.
CRP (C-Reactive Protein)
What it is: A test that measures the concentration of a protein called c-reactive protein in the blood. The higher the concentration, the more severe the inflammation.
Why doctors order it: To figure out the extent of inflammation. Because the test is sensitive and responds rapidly to changes in inflammation, your child’s doctor may use it to monitor her disease activity and response to treatment.
Test limitations: The CRP goes up any time there is inflammation, including when your child has a cold.
ESR (Erythrocyte Sedimentation Rate – also called “sed rate”)
What it is: A test that measures how fast RBCs, or erythrocytes fall and settle, like sediment, at the bottom of a test tube. The presence of inflammatory factors affect the rate at which the cells fall. The more inflammation in the body, the higher the ESR.
Why doctors order it: Because a high ESR, like a positive CRP, indicates the presence of inflammation. In a child already diagnosed with arthritis, a doctor may use the test to monitor disease activity or response to treatment. A lower sed rate would indicate inflammation is being controlled.
Test limitations: The ESR is less sensitive than the CRP and doesn’t respond as quickly to changes in inflammation, so many doctors prefer the CRP.
Leave a Comment