A ‘late’ diagnosis is one which is made at a point in time after which HIV treatment should have been started. In 2012, among those newly diagnosed, 47% were diagnosed late (with a CD4 cell count below 350 cells/mm³), including 28% who were diagnosed very late (with a CD4 cell count below 200 cells/mm³).

Inequalities are apparent – while 34% of gay and other men who have sex with men were diagnosed late, rates are much higher in heterosexual men and women. They are particularly high amongst black African heterosexuals, many of whom are likely to have acquired HIV before their arrival in the UK. In 2012, 66% of black African men and 61% of black African women were diagnosed late.

Older adults are over-represented amongst those diagnosed late – 63% of people who are diagnosed over the age of 50 have CD4 cell counts lower than 350 cells/mm³.

Over the past decade, the proportion of individuals diagnosed late has declined significantly, from 58% in 2003 to 47% in 2012. The decline has been seen in all exposure groups, but especially in MSM.

The public health performance of local authorities will be judged, in part, on actions to reduce late diagnosis of HIV. The Public Health Outcomes Framework includes the proportion of people newly diagnosed with HIV who have a CD4 count below 350 or who develop AIDS within three months of diagnosis as an outcome ‘indicator’. This is intended to focus decision makers’ attention on the issue of HIV testing.

Because of this, Public Health England publishes data for each local authority on late diagnosis, highlighting disparities between different areas. For example, the neighbouring London boroughs of Tower Hamlets, Hackney and Newham have late diagnosis rates of 33, 45 and 60% respectively. Whereas Blackpool has a late diagnosis rate of 29%, in Salford, 51% of diagnoses are late.

Reducing late diagnosis is important because not taking treatment until the immune system is severely weakened increases the chances of developing serious, life-threatening illnesses.

Analysis of the SMART study showed that people who delayed treatment until their CD4 cell count was below 250 cells/mm³ had a four-fold greater risk of opportunistic infections and serious non-AIDS clinical events, compared to people who started treatment with a CD4 cell count above 350 cells/mm³. A ten-year analysis of deaths in people with HIV in the United Kingdom found that individuals diagnosed with a CD4 cell count below 350 cells/mm³ were ten times more likely to die of AIDS. The researchers estimate that 81% of all AIDS-related deaths and 61% of all non-AIDS-related deaths were caused by late HIV diagnosis. Moreover, there is a particular risk of mortality for older adults who are diagnosed late.

However, the risk of illness and death is concentrated in the first year after being diagnosed – if people start treatment and get through the first year, longer-term outcomes are good.

In terms of life expectancy, people starting HIV treatment with a CD4 cell count below 100 cells/mm³ live 15 fewer years than people starting treatment at a CD4 cell count between 200 and 350. People starting treatment with between 100 and 200 cells/mm³ live for 12 fewer years.

Each new case of HIV infection costs the NHS between £280,000 and £360,000 over a lifetime. But costs are greatest for individuals diagnosed late – in the first year after diagnosis, spending is doubled for those diagnosed with a CD4 count lower than 200 cells/mm³. This is largely due to increased inpatient hospital care costs, as well as the cost of extra investigations, immediate antiretroviral therapy and drugs for medical conditions caused by immunosuppression.

Late diagnosis is also a problem for onward transmission. As an individual becomes increasingly immunocompromised, viral load rises, so he or she is more infectious until effective treatment is taken.