Xrays if trauma, may consider for all to rule out bone spur as causative agent (although not emergent)
Initial aspiration is controversial.  There is currently no consensus on the optimal diagnosis strategy for prepatellar<unk> .  The majority of patients studied did receive an aspiration of fluid (82%), but those patients had a significantly higher rate of complications (persistent infection, secondary infection in initially aseptic bursae) than patients treated with antibiotics alone.
If any signs of infection, must aspirate to rule out septic<unk> 
If no signs of infection:
May consider initial conservative (no aspiration) treatment for several days
Some sources suggest aspiration for all cases
If any signs of infection, must aspirate to rule out septic<unk> 
If no signs of infection:
May consider initial conservative (no aspiration) treatment for several days
Some sources suggest aspiration for all cases
May consider initial conservative (no aspiration) treatment for several days
Some sources suggest aspiration for all cases
Olecranon bursitis 
Distal humerus fracture
Calcaneal bursitis
Radial head fracture
Hip bursitis
Essex-Lopresti fracture
Pes anserine bursitis
Capitellum fracture