There isn't a blood or urine test for osteoarthritis, the symptoms picture is used to diagnose.
I expect the doctor may have mentioned osteoarthritis of the lower back which would be consistent with the description of your symptoms.
However, similar symptoms may present as a result of lower back pain too as circulation to the limbs can be impaired in either case.
I donned the gym kit last week to demonstrate some mobility and strengthening exercises for the lower back and you should find the video on our website within a few days but please visit our lumbago section in the meantime.
The only way you'll get a definitive diagnosis is via an MRI scan which can show increased joint spaces between the vertebrae (osteoarthritis) or soft tissue damage (sprain/strain).