The classification of cells by five types of histograms is the simplest and most generally accepted method in current use at M.D. Anderson Cancer Center.
 

	U1: These histograms are characterized by a single DNA content peak in the diploid (2c) region. Only a few cells may deviate from the normal value.
	U2: These histograms are characterized by one peak in the diploid (2c) region, with a few cells (up to 15%) outside the normal DNA content value; these latter cells have a DNA content in the 5c region or greater.*
	U3a: This type of histogram differs from U2 by having a significant number of cells with an aneuploid DNA content (values between 2c and 4c and cells greater than 5c.)**
	U3b: These histograms reveal pronounced tetraploid subpopulations (tetraploid DNA content cells comprise at least 10% of population with corresponding octaploid peak.)***
	U4: Polyploid DNA pattern (i.e., peak(s) at 2c, 4c, 6c, 8c, and even 10c). U4 polyploid pattern is most typically associated with viral cytopathic effect.

^*: U2 intermediate patterns have a strong positive prediction for presence of histologically confirmed or cystoscopically visualized neoplasm(s). In a few cases, the underlying neoplasm may be initially occult. However, it will manifest itself over a sufficiently long follow-up time.) Occasionally this pattern may be seen with lithiasis (stones), therapy effect, or in specimens containing seminal vesicle cells; hence, clinical correlation is essential.

^**: U3a clearly shows aneuploid pattern(s). Sensitivity (>90%) for carcinoma in situ and invasive TCCs (or its variants). 

^***: U3b shows tetraploid pattern slightly less sensitive than U3a for predicting the presence of neoplasm.