Patient Articles

Laboratory Tests

Used in the Diagnosis and Treatment of Rheumatic Diseases

Laboratory tests are an important part of your treatment. They help your doctor:

  Diagnose your health status correctly.
  See how your health changes over time.
  Find side effects of the medications you take.

Blood Testing

You may need to have several of these tests. One blood sample may be enough for several tests. You may be used to many of them. They may have been part of other health checkups you had over the years.

Complete Blood Count (CBC)

This test measures the number and types of blood cells:
- White blood cells (WBCs): Changes in WBCs can mean that you have an infection, inflammation, or that not enough WBCs are made. Rheumatic diseases can cause WBC count to be too high or too low.
- Red blood cells (RBCs). A decrease in RBCs, hemoglobin (Hgb), and hematocrit (HCT) can be a result of loss of blood or bleeding, or from ongoing inflammation. A low RBC count can also indicate serious side effects of medications called DMARDs. Intestinal bleeding can cause these decreases too. There are many reasons why patients have intestinal bleeding. Sometimes bleeding comes from problems in the intestine such as ulcers, polyps or tumors. Sometimes medications, such as aspirin, anticoagulants, or nonsteroidal anti inflammatory drugs may increase the risk of intestinal bleeding. Low red blood cells is also called anemia. Patients with anemia may be tired, listless, weak, or feel short of breath or lightheaded, and may appear pale. However, most patients do not have such symptoms and therefore it is important to comply with testing when monitoring your red blood count.
- Platelets. Autoimmune diseases can decrease the number of platelets. Some medications also can lower your platelet count. Platelets help your blood to clot. Having not enough platelets can make you bruise or bleed easily.

Blood cells are made in the bone marrow. Many medications you take can slow down activity in the bone marrow. Therefore, your CBC must be checked regularly.

Tests for inflammation

C-reactive Protein (CRP)

The CRP measures inflammation in your blood. It can help your doctor tell apart different diseases. If the CRP is high, you have an inflammatory disease, maybe an autoimmune disease. If the CRP is low, you may not have inflammation. The pain in your joints may be due to wear and tear, instead.

The CRP should become lower after you begin your medication. Decreasing CRP levels show that the medication is reducing the inflammation in your body.

Erythrocyte Sedimentation Rate (ESR)

This test is similar to the CRP test. It also measures inflammation in your blood.

Important: It is possible to have inflammation, and yet have normal results on either or both the CRP and ESR. Scientists do not understand all the reasons why that happens, but it does. So, your doctor may conclude you have inflammation even when the tests are not abnormal.

Sometimes the tests may be abnormal, and yet your doctor may not find a source of inflammation. The ESR in particular tends to be higher as people get older, and being overweight or having other health problems may cause the ESR to be somewhat higher than normal without indicating inflammation.

The tests do not tell your doctor what parts of your body are inflamed. More than one problem can cause inflammation at the same time. A patient can have active arthritis, and get an infection. Infections cause inflammation. Thus, your doctor may have to examine you and question you and do more tests to find out the reasons for inflammation under some circumstances.

Creatinine Phosphokinase (CPK) & Aldolase Test

These blood tests measure inflammation or damage in your muscles. The CPK can also show how well your medications work for you.

Kidney Function Test (Creatinine Test and BUN, urinalysis)

A creatinine test or a BUN measures the health of your kidneys. A urinalysis also helps your doctor know about your kidneys and your bladder – see below. Some rheumatic diseases (eg, lupus) can harm your kidneys. Medications (eg, NSAIDs) can also damage your kidneys, especially when you take them for a long time. When you have diabetes or high blood pressure, your kidneys are more vulnerable. The same is true as you get older. For people with vulnerable kidneys, regular kidney checkups are a normal part of treatment.

Liver Function Tests (AST, ALT, alkaline phosphatase)

These tests measure the health of your liver. Some autoimmune diseases can harm your liver. But this rarely happens. More often, the liver is damaged by some medications, if you take them for a long time. Having high cholesterol can cause abnormal tests, and doctors call this a fatty liver.

Liver function tests are used to make sure your liver stays healthy, when you take these medications. When you take methotrexate and NSAIDs (non-steroidal anti-inflammatory drugs), liver tests are a normal part of your treatment.

Uric Acid Test

You may need this test, if your doctor suspects that you have gout. In gout, uric acid levels in your blood are high. The uric acid test measures the amount of uric acid in your blood.

Many people with gout take medication to reduce uric acid in their blood. When you are taking medications, this test is done to check whether they are working.

Joint Fluid Testing

Your may need to give a sample of your joint fluid. The fluid is then tested to see whether you have an infection or inflammation in your joint. This test is helpful in diagnosing who may have gout. In gout, there are uric acid crystals in the joint fluid. A joint fluid test can detect these crystals, or other types of crystals that can cause inflammation.

Tuberculosis (TB) Testing

Everyone must have a TB test before taking biologic medications (biologics). The TB test is either a skin test or a blood test.

For the skin test, the test fluid is “stamped” into your skin with several tiny needles. Then, you wait several weeks to see whether you develop tiny bumps on the skin where you got the stamp. There is another TB test, called the QuantiFERON®-TB Gold test. For this test, you give a blood sample. Each test works better for some people. Your doctor will choose the one that is best for you.

Urine Testing

All people seeing their doctor need to give urine at their first visit. You may also have to get a urine test after you have not seen your doctor in a while. This is an easy, quick test to see whether you have an infection. While you are taking medications, this test is used to make sure your kidneys are staying healthy.