Provided is a derivative of 22-hydroxycholesterol, 24S-hydroxycholesterol, 25-hydroxycholesterol, 26-hydroxycholesterol or 27-hydroxycholesterol. Also provided is a protein conjugated to the above derivative. Further provided is an antibody composition comprising antibodies that specifically bind to 22-hydroxycholesterol, 24S-hydroxycholesterol, 25-hydroxycholesterol, 26-hydroxycholesterol or 27-hydroxycholesterol. Additionally, a method of making antibodies that specifically bind to 22-hydroxycholesterol, 24S-hydroxycholesterol, 25-hydroxycholesterol, 26-hydroxycholesterol or 27-hydroxycholesterol is provided. Also, a method of assaying for 22-hydroxycholesterol, 24S-hydroxycholesterol, 25-hydroxycholesterol, 26-hydroxycholesterol or 27-hydroxycholesterol is provided. Additionally provided is a kit for detecting 22-hydroxycholesterol, 24S-hydroxycholesterol, 25-hydroxycholesterol, 26-hydroxycholesterol or 27-hydroxycholesterol. A method of detecting an enzyme or enzymes utilized in phase II drug metabolism is also provided. Also, a method of detecting an enzyme that synthesizes 22-hydroxycholesterol, 24S-hydroxycholesterol, 25-hydroxycholesterol, 26-hydroxycholesterol or 27-hydroxycholesterol is provided. Further provided is a method of evaluating progression of multiple sclerosis in a patient. Also provided is a method of determining whether a treatment for multiple sclerosis in a patient is effective. Further, a method of evaluating progression of Huntington's disease in a patient is provided. Additionally provided is a method of determining whether a treatment for Huntington's disease in a patient is effective.