Understanding Routine Lab Tests for RA

By Beth Axtell

Sometimes it can feel like you’ve been poked, prod¬ded and have had enough blood drawn to feed a million mosquitoes. Now that you have a rheumatoid arthritis (RA) diagnosis, you may have hoped you could give the phlebotomist a Starbucks gift card and say goodbye. 

Then, you find out that having a diagnosis in hand won’t put an end to bloodwork. Your rheumatologist uses regular tests to monitor disease activity, check for medication effects and screen for common comorbidities. 

Maria Danila, MD, associate professor of medicine at the University of Alabama at Birmingham, says that once she has diagnosed a patient, she runs a series of tests to get baseline values before she starts any treatments. As part of a treat-to-target treatment protocol, she sees her patients frequently and makes therapy adjustments until a goal is reached — usually remission  or low disease activity. Assessing disease activity and taking regular lab tests are part of that process.

Other lab tests help to determine if any medicines are damaging your organs. How frequently you’ll have these tests depends on the medicines you take.

Here’s a run-down of the most common lab tests your doctor may order and what they look for. 
 

Erythrocyte sedimentation rate (ESR) is commonly called “sed rate.” This blood test measures the amount of inflammation in your body. It measures how fast red blood cells cling together and settle to the bottom of a tube over the course of an hour, indicating inflammation. Many factors can interfere with the results, such as an infection and age.

C-reactive protein (CRP) also measures inflammation. CRP is a protein produced by the liver when there is inflammation anywhere in the body. The more inflammation, the higher the CRP is. This test, however, can be influenced by factors such as obesity and infection. 

Neither ESR nor CRP is specific to RA, but both are used to help determine disease activity. Dr. Danila says the two measures don’t always correlate with one another or with how you may be feeling. 

“At each visit, I evaluate symptoms and examine for tender and swollen joints. I assess the patient’s perception of disease activity and we order labs. Over the first several visits, I measure sedimentation rate and CRP. If I think one marker correlates better with disease activity for a patient, I monitor only that one over time.” 

Several RA medications can be toxic to your liver, and biologics may re-activate a dormant hepatitis virus. Your doctor will check your blood for evidence of hepatitis B or C infection before prescribing most RA medicines. You may also be monitored for hepatitis from time to time throughout treatment.

Before starting you on a biologic drug, your doctor will check for tuberculosis (TB) with a skin test, blood test or X-ray. Even if you’ve never had symptoms of TB, the bacteria can lie dormant in your body for many years. Taking medications that suppress the immune system increases the risk the infection will become active. Your doctor may continue to monitor for TB throughout treatment.

A complete blood count (CBC) looks at white blood cells, which help fight infection; platelets, which are needed to clot blood; red blood cells, which carry oxygen throughout the body; and hemoglobin, the protein in red blood cells that carries oxygen. 

Anemia is common in people with RA. It’s a condition in which the body doesn’t have enough healthy red blood cells. Dr. Danila says that certain medicines (like methotrexate, leflunomide and sul-fasalazine) can be harmful to bone marrow, where new blood cells are made. Leukopenia (low white blood count) and thrombocytopenia (low platelet count) are also sometimes seen in people taking biologic medicines. 

Measuring blood levels of certain proteins and liver enzymes can help doctors determine if medications have damaged the liver or if hepatitis has been re-activated. A liver panel checks for albumin, a protein made by the liver; bilirubin, a component of bile that is made by the liver; and liver enzymes, including alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP) and gammaglutamyl transpeptidase (GGT). 

Treatment with interleukin inhibitors  (such as sarilumab or tocilizumab) and JAK inhibitors  (tofacitinib) can affect triglyceride and cholesterol levels. Your doctor will check these levels and may prescribe a medication to lower them if needed.

Dr. Danila says that active inflammation may decrease your lipid serum levels. She explains that you may need to re-check your lipid levels after your RA inflammation is under control. 

To screen her patients for potential heart disease — a common comorbidity of RA — Dr. Danila says, “I look at lipid panels and monitor blood pressure in any patient with RA, whether or not they take medications that may affect their lipid levels.”

Kidney function is determined by measuring the levels of creatinine and urea nitrogen in the blood. Both are normal waste products of the body. High levels mean the kidneys are not working well enough to remove them from the body. Anti-inflammatory drugs may affect kidney function, and some medicines, like methotrexate, are eliminated through the kidney and may cause toxicity when kidney function is abnormal. 

A blood sugar level is part of every blood chemistry panel — the test your doctor orders to look at kidney and liver function. Although your doctor may not be looking for your risk of diabetes, she will be alerted to abnormal blood sugar levels just by running a “chem panel.”

The MBDA test (Vectra DA) was developed by a biotechnology company to look at the chemical factors in your body that drive rheumatoid arthritis activity. It checks 12 proteins, hormones and growth factors and gives your doctor a single disease activity score. Dr. Danila says many clinicians use a combination of physical assessment (swollen and tender joint counts) and inflammation levels (CRP and sed rate) rather than Vectra DA to check disease activity. But recent studies found that the MBDA test can be used to gauge how aggressive your disease is, how likely you are to have a flare when stopping medications and what drug combinations may work best.