CPT® Code 88364

Add-On Code

In situ hybridization (eg, FISH), per specimen; each additional single probe stain procedure (List separately in addition to code for primary procedure)

In situ hybridization (FISH) is a specialized laboratory technique utilized to identify and localize specific nucleic acid sequences, including DNA and RNA, within fixed tissue samples or cells. This method provides critical temporal and spatial information regarding gene expression and genetic coding, which is essential for understanding the organization, regulation, and functional roles of genes within biological systems. The process begins with the fixation of sample cells or tissues to preserve the target transcripts in their original locations. Following fixation, a DNA or RNA probe is introduced, which hybridizes, or binds, to the target nucleic acid sequence at an elevated temperature. After hybridization, any unbound excess probe is washed away, leaving only the bound probes attached to the target sequences. The remaining DNA or RNA targets are then stained using spectrally distinct fluorophore labels, allowing for visualization under fluorescent microscopy. This technique is particularly valuable in genetic analysis, as DNA-FISH can reveal the presence, copy number, and location of genes, while RNA-FISH can provide insights into gene expression and the temporal and spatial localization of RNA within the specimen. The FISH technique is versatile, enabling the simultaneous use of multiple probes to visualize co-locations of different targets within a single specimen. In the context of coding, CPT® Code 88365 is designated for the initial single probe stain per specimen, while CPT® Code 88364 is specifically used for each additional single probe stain performed, and CPT® Code 88366 is applicable when multiple probes are utilized in the same staining procedure.