There is currently no blood test for early-stage osteoarthritis, a degenerative joint disease where the cartilage that eases and cushions movement breaks down, causing pain, swelling, and problems moving the joint. Now, researchers at Warwick University in the United Kingdom have developed a blood test that can provide an early diagnosis of osteoarthritis and distinguish it from rheumatoid arthritis and other inflammatory joint diseases.
The researchers, led by Dr. Naila Rabbani of Warwick Medical School, report how they developed the new blood test in the journal Arthritis Research & Therapy.
The test could be available within 2 years, say the researchers. The earlier that arthritis is diagnosed - before physical and irreversible symptoms set in - the better the chances that treatment can focus on how to prevent the problem, for instance with lifestyle changes.
The new blood test looks for chemical signatures in fragments of joint proteins (amino acids) that have been damaged, as Dr. Rabbani explains:
"The combination of changes in oxidized, nitrated and sugar-modified amino acids in blood enabled early stage detection and classification of arthritis - osteoarthritis, rheumatoid arthritis or other self-resolving inflammatory joint disease."
Dr. Rabbani notes that scientists have known for a while that proteins in the arthritic joint get damaged, but this is the first time they have looked at them from the point of view of early disease diagnosis.
"For the first time we measured small fragments from damaged proteins that leak from the joint into blood," she adds.
High sensitivity and specificity for early-stage diagnosis
For the study, the team recruited 225 participants. These included patients with knee joint early-stage and advanced osteoarthritis and rheumatoid arthritis or other inflammatory joint disease, and healthy volunteers with no joint problems.
- Osteoarthritis is the most common form of arthritis
- In the United States, an
estimated 30.8 millionadults had osteoarthritis from 2008 to 2011
- Nearly 1 in 2 Americans may develop symptomatic knee osteoarthritis by age 85 years.
Using mass spectrometry, the researchers analyzed samples of blood and synovial fluid (from the affected knee joints) for oxidized, nitrated, and sugar-modified proteins and amino acids.
They found some patterns of damaged amino acids in samples from patients with early and advanced osteoarthritis and rheumatoid arthritis that were markedly lower in samples from the healthy volunteers.
Using sophisticated bioinformatic computer methods, they developed algorithms - based on 10 damaged amino acids - that can diagnose early-stage osteoarthritis, rheumatoid arthritis, and non-rheumatoid arthritis.
The researchers note the new blood test has a "relatively high sensitivity and specificity for early-stage diagnosis and typing of arthritic disease."
Sensitivity is the extent to which a negative result is able to rule the disease out, and specificity is the extent to which a positive result can rule the disease in.
In the case of early-stage osteoarthritis, the study found the blood test had a sensitivity of 92 percent and a specificity of 90 percent. These compare favorably with current techniques.
For instance, in their background information, the researchers note that current magnetic resonance imaging techniques for evaluating cartilage damage in early-stage osteoarthritis have sensitivities around 70 percent and specificities around 90 percent.
Also, compared with a blood test, such techniques are expensive and time-consuming, and cannot be used with some patients - for instance, those fitted with pacemakers.
"This is a big step forward for early-stage detection of arthritis that will help start treatment early and prevent painful and debilitating disease."
Dr. Naila Rabbani