Photographic densitometry for quantitative DNA analysis of cytologic and histologic specimens.

We found that photographic densitometry (PD) is a useful technique for quantitative determinations of nuclear DNA content in clinical tumor material. Optimum conditions for the use of PD in clinical cytology and histopathology were worked out. A quantitative evaluation of the method was performed, particularly with respect to errors that may appear when measuring clinical tumor material. Our study showed that PD offers accurate DNA measurements in cytologic and histologic specimens. Ploidy level determinations in tumor cell populations in clinical material could be as accurately performed with PD as with scanning microspectrophotometry (SMP). Nuclear DNA content of individual cells as determined by PD correlated highly with nuclear DNA content determined by SMP (correlation coefficient, 0.96). Since the PD method is less influenced by background variation than are other image techniques (due to measurement of a photographic image), it is particularly useful in measurement of histopathologic sections, in which the background variation can introduce considerable errors. The method is also valuable with clinical cytologic smears, in which the presence of blood and other material disturbs the background. PD represents a valid complement to scanning microspectrophotometry and TV imaging systems, particularly for DNA analysis of tissue sections. Moreover, it can be applied easily in the clinical routine. Relevant tissue areas are selected and photographed by the pathologist or cytopathologist, and the measurement is performed by a laboratory technician.