Which of the following conditions could the creatine kinase blood test be used to determine? 

• A. Fibrosarcoma 
• B. Myositis 
• C. Osteosarcoma 
• D. Optic neuritis 

Answer: (B)

Verified step by step guidance

1. Step 1: Understand what creatine kinase (CK) is — it is an enzyme found mainly in the heart, brain, and skeletal muscles, and its levels in the blood increase when there is muscle damage.
2. Step 2: Recognize that the creatine kinase blood test is primarily used to detect muscle injury or inflammation, as elevated CK levels indicate muscle cell damage.
3. Step 3: Review the conditions listed: Fibrosarcoma (a malignant tumor of fibrous tissue), Myositis (inflammation of muscle), Osteosarcoma (bone cancer), and Optic neuritis (inflammation of the optic nerve).
4. Step 4: Identify that among these, Myositis involves muscle inflammation, which would cause elevated creatine kinase levels detectable by the CK blood test.
5. Step 5: Conclude that the creatine kinase blood test is useful for diagnosing or monitoring Myositis because it reflects muscle damage or inflammation, unlike the other conditions listed.