There has been a recent shift in what is classified as a late diagnosis following 2008 British HIV Association guidelines.

A late diagnosis now means having a CD4 count below 350 cells/mm3 within 30 days of diagnosis.  However previously it meant having a CD4 count below 200 cells/mm3 within 30 days of diagnosis.

Using the new definition, the majority (3,970 of 7,220) of adults aged over 15 who were newly diagnosed in 2008 were diagnosed late.

How does this vary by probable exposure category?

The proportion of late diagnoses is lowest among men who have sex with men and highest among heterosexual men. 
 

Probable exposure category	% of newly diagnosed adults over 15 in 2008 that had a CD4 count below 350 cells/mm3 within 30 days of diagnosis	% of newly diagnosed adults over 15 in 2008 that had a CD4 count below 200 cells/mm3 within 30 days of diagnosis
Men who have sex with men	43%	20%
Heterosexual women	61%	36%
Heterosexual men	66%	44%
Injecting drug users	52%	30%
Overall	55%	32%

This information is based on estimations made by the Health Protection Agency, sourced from their HIV in the United Kingdom: 2009 report.