A bone marrow biopsy is a painful procedure in which marrow is removed from bone and examined. A doctor who performs a bone marrow biopsy most likely wants to observe which of these?

Bone marrow is the tissue inside bones where many blood cells are made, including leukocytes (white blood cells). Examining a marrow sample lets a doctor assess the cells being produced there. Lymph and interstitial fluid are fluids, while the thymus is a separate organ.

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