In this VETgirl online veterinary continuing education blog, we demonstrate how to perform a joint tap in a dog. This is a relatively simple procedure, that can be easily performed by veterinarians under sedation using aseptic technique. This should be done in any patient with joint swelling, especially if Lyme disease has been ruled out. Before just routinely putting a dog on prednisone and doxycycline, a joint tap should be performed to rule out immune-mediated joint disease (IMJD) versus other underlying causes (e.g., septic joint, rheumatoid arthritis, etc.). That's because the treatment will be markedly different depending on the underlying etiology. Remember to look at that cytology in-house before you submit it for fluid analysis and culture. Typically, with IMJD, neutrophilic inflammation is seen on cytology.