The present invention describes semi- and fully-automated methods and reagents therefor for the assay and analysis of body fluid samples, particularly non-blood samples. The methods and reagents are especially useful for the assay and analysis of cerebrospinal fluid (CSF) samples. The reagent compositions sphere and fix all cells in the sample in suspension. Reported results can include red blood cell (RBC) and white blood cell (WBC) counts, WBC differential values, cell-by-cell volumes and dry-mass concentrations.