Yes arthritis can be detected in a blood test.
One of the tests that are used to detect arthritis is a blood test that is taken and then sent off to the lab for testing.
X Rays and MRI's as well as various types of angiograms are used as tests to diagnose and detect arthritis but your arthritis can be detected through blood tests.
But you may need more tests such as the X Ray, etc to fully and properly diagnose and detect the arthritis.
Some forms of arthritis can get by with just the test of testing through the blood while other forms of arthritis may need more than the blood tests.