Question: Maryland Subscriber Answer: Although CPT does not list 88280 with a "+" to designate that it is an add-on code, it functions as an add-on. Cytogenetic codes 88230-88299 are "building block" codes. You should select the appropriate codes in the range that describe each step that your lab performs for a complete cytogentic study. For instance, you might report: • 88237 (Tissue culture for neoplastic disorders; bone marrow, blood cells) for the tissue culture step • 88261 (Chromosome analysis; count 5 cells, 1 karyotype, with banding) for the first karyotype analysis, and • 88280 for one additional karyotype analysis. Because 88280 states "additional karyotypes," you should use the code only with a base code that describes the first karyotype(s) (88261-88269).