What likely caused the presence of several nucleated RBCs after centrifugation of a spinal fluid sample in a 56-year-old woman?

The presence of several nucleated red blood cells (RBCs) in a spinal fluid sample typically indicates an issue related to the handling of the sample or a pathological process occurring in the body. In this case, bone marrow contamination is a plausible explanation. If the spinal fluid was contaminated during the collection process—perhaps due to trauma or improper technique—it could result in the introduction of nucleated RBCs from the bone marrow.

Nucleated RBCs are normally found in the bone marrow, where they are generated during erythropoiesis. Under normal circumstances, they are not present in healthy spinal fluid. Therefore, their presence after centrifugation suggests that they were not a product of normal central nervous system activity, but rather a result of contamination at the time of sample collection. This potentially implies that the spinal fluid specimen was contaminated with peripheral blood, which can introduce nucleated RBCs among other cellular components.

While bacterial meningitis and leukemic infiltration could lead to changes in cell types found in spinal fluid, they would be characterized by the presence of other inflammatory or malignant cells rather than just nucleated RBCs alone. Peripheral blood contamination could also contribute to the presence of nucleated RBCs, but the option emphasizing bone marrow contamination directly points to