PCR In Situ Hybridization

In situ hybridization is the only molecular biology based test that allows for the direct correlation of the results with the histologic and cytologic features of the sample. The DNA/RNA extraction that precedes filter hybridization (slot blot or Southern blot) and PCR precludes this analysis. The relative sensitivities of the three different assays are presented in Table 1. It is evident that in situ hybridization is a relatively insensitive test. A reflection of this relative insensitivity is seen in occult or latent infection by a virus where the copy number is low. In such situations, the virus is rarely detected by in situ hybridization even though it was detected by either PCR or filter hybridization (1– 6). This is not to say that the technique of in situ hybridization has remained static. The detection threshold of this assay has improved substantially in the last 5 yr. Another point worth emphasizing about in situ hybridization is that one does not need to use radiolabeled probes (usually 35S or 3H) in order to maximize