Final answer:
An UNEXPECTED laboratory value indicating osteomyelitis in a client with a compound fracture is an increased white blood cell count, which should be reported to the provider as it suggests the presence of an infection.
Step-by-step explanation:
A nurse providing follow-up care for a client with a compound fracture might encounter various laboratory values during their assessment. However, among the options provided, an UNEXPECTED finding that would be indicative of osteomyelitis, an infection in the bone, would be an increased white blood cell count. This would suggest that the body is fighting an infection, which is consistent with the presence of osteomyelitis.
On the contrary, elevated hemoglobin level, decreased platelet count, and decreased erythrocyte sedimentation rate (ESR) are not typically associated with osteomyelitis. Therefore, if a nurse finds an increased white blood cell count in a patient three weeks post-compound fracture, this should be reported to the healthcare provider as it may indicate the development of an infection such as osteomyelitis.