What is it?
Osteoarthritis (OA) is the most common form of arthritis, affecting about 20 million people in the United States. Also called degenerative joint disease (DJD), OA is associated with joint injury and with the aging process. It is a chronic disease that causes deterioration of the joint cartilage and the formation of new bone (bone spurs) at the edges of the joints. Cartilage and synovial fluid are meant to provide a smooth, low friction transition between the ends of bones. When cartilage loses its elasticity and wears down, joint movement becomes less smooth. Eventually cartilage can completely erode and the opposing bone ends can rub together. This leads to pain that may be intermittent or chronic, to stiffness in the morning and after rest, to small pieces of bone and fragments of cartilage in the remaining synovial fluid, and to a loss of mobility.
OA occurs equally in men and women before age 55 but more often in women after that age. It is also common in athletes who sustain multiple joint injuries over time. The primary cause is mechanical (for example, joint damage caused by running or excess weight-bearing) but, more rarely, it may be metabolic, genetic, or chemical in nature. Obesity, muscle weakness, and other diseases such as rheumatoid arthritis and hemochromatosis can increase the risk of developing OA and can exacerbate the symptoms associated with it. The joints most commonly affected by OA are those of the hips, knees, hands and fingers, big toe, neck, and lower back.
Tests
The goal of testing is to diagnose OA, to distinguish it from other forms of arthritis and causes of joint pain and stiffness, and to monitor the side effects of various treatments.
Laboratory Tests
There is no specific laboratory test to diagnose OA. It is diagnosed by a doctor using a patient’s medical history, a physical exam, X-rays, and in some cases with an examination of synovial fluid from an affected joint. Tests that may be ordered to rule out other conditions and to evaluate the patient’s health include:
Rheumatoid factor (RF) and Cyclic Citrullinated Peptide Antibody (CCP) – used to help diagnose rheumatoid arthritis and differentiate it from osteoarthritis.
Synovial fluid analysis – to detect crystals that may be present in the joint and to look for signs of joint infection.
Erythrocyte sedimentation rate (sed rate or ESR) – this test shows the presence of inflammation in the body. ESR will be increased in RA but not in osteoarthritis.
C-reactive protein test (CRP) —this test also indicates inflammation and tests for the activity of the disease. It may be used to help differentiate osteoarthritis and RA. An increased level of CRP occurs in RA but not in osteoarthritis.
Complete Blood Count (CBC) – this is a group of tests that are used to help evaluate the patient’s red and white blood cells and hemoglobin. It may be ordered to monitor the side effects of some OA treatments.
Comprehensive Metabolic Panel (CMP) – this is a group of tests that may be used to help evaluate and monitor the patient’s kidney and liver function.
Non-Laboratory Tests
X-rays of the affected joints may show loss of cartilage and narrowing of the joint space but will frequently not show significant changes early in the disease.
MRI (magnetic resonance imaging) – may also be used to examine affected joints.