UA (Urinalysis)

What it is: A test in which urine is examined under a microscope.

Why doctors order it: Because some medications are metabolized or excreted by the kidneys, the doctor will use a urinalysis to be sure the kidneys aren't overburdened. Doctors also use the test to look for and monitor lupus-related kidney disease.

 

CPK (Creatinine Phosphokinase)

What it is: A test used to detect the presence of one of several enzymes released from muscle cells when they are damaged by inflammation.

Why doctors order it: An elevated CPK raises the suspicion for juvenile dermatomyositis (JDM), because muscle inflammation and subsequent damage are the hallmarks of JDM. The test also measures a medication’s effectiveness in reducing the inflammation that caused the damage.

 

LFT (Liver Function Test)

What it is: A test that determines whether the liver is healthy and functioning normally. The most commonly ordered tests are liver transaminases, which measure damage to the liver.

Why doctors order it: Because many medications used to treat arthritis (methotrexate, in particular) are metabolized in the liver and may overburden the liver, your child’s doctor may order regular LFTs to determine if the medications are causing any damage.

 

HLA (Human Leukocyte Antigen) – B-27 typing

What it is: A blood test used to detect the presence of a B27 variant of a gene involved in immune regulation.

Why doctors order it: Detection of HLA-B27 tells the doctor that a child has a genetic marker associated with a spondyloarthropathy, such as ankylosing spondylitis (AS) or a related condition known as enthesitis related arthritis (ERA) or seronegative arthritis and enthesopathy (SEA) syndrome. These syndromes are frequently suspected in older children (boys more than girls) with hip and knee arthritis and back pain. Ninety-five to 98 percent of patients with AS have a positive HLA-B27, as do 50 percent of those with other spondyloarthropathies.

Test limitations: Eight percent of Caucasians have a positive HLA-B27, while far less than one percent actually develop arthritis.