Thousands of ethnic women in the world's poorest countries are dying from HIV/AIDS, TB, malaria and maternal problems because governments and international bodies fail to record their health outcomes.
Many more women's lives remain in peril amid efforts to meet the 2015 deadlines for the UN Millennium Development Goals and beyond them.
And some communities in countries described as middle income states face the danger of abandonment by international donors, in spite of their worsening health plight.
This warning is signalled today as the charity Health Poverty Action launches a new report, hours before the UN starts New York discussions over five days on a new set of goals to replace the MDGs after 2015, covering topics including inequality.
The report Tackling inequality in global health: Why we must break down health data by ethnicity, states that current methods of data collection, which fail to break down health information by ethnic group, are covering up huge disparities between the health of ethnic minorities and majority populations.
It cites life expectancy at just 52 years among Namibia's semi-nomadic indigenous San people, compared to 79 years for the country's German-speaking population.
Surveys published in Namibia provide no information about health outcomes by ethnic group.
The district of Tsumkwe, in north-east Namibia, has the largest concentration of San people, with crowded living conditions and sleeping without insecticide-treated nets contributing to high levels of HIV/AIDS, TB and malaria.
According to Health Poverty Action, a low proportion of San people living with HIV/AIDS take antiretroviral drugs.
The uptake of treatment to prevent mother to child transmission lags behind the rest of the country.
Deadly TB strains have spread amid the regular failure of TB sufferers in mobile San communities to complete their treatment.
The charity's report says the measurement of progress towards the MDGs by national averages, drawn from whole populations, masks health variations among different ethnic groups within each country, hiding communities at risk.
Though the MDG target of halting and starting to reverse the spread of HIV has been met, 2.3 million people are newly infected by the virus each year, with 1.6 million of them in sub-Saharan Africa.
Similarly, the overall tuberculosis mortality rate fell 41 per cent in the decade from 1991, yet in 2011 the illness killed 1.4 million people and access rates to treatment remain too slow.
Progress towards the MDG of cutting maternity mortality by three quarters is also slow - only half of pregnant women in developing regions receive the advised minimum of four antenatal care visits and many lack a skilled birth attendant.
Health Poverty Action calls for:
- indicators to gauge progress against all the post-2015 development framework goals to be broken down by inequity, including ethnic and cultural groups.
- governments like the UK, to support developing countries, including middle income countries, to invest in better statistics collection and analysis, so that inequities between groups, such as ethnic minorities, can be tracked and addressed, with a standalone equality goal to be included in the framework.
- goals to address the root causes of inequality, such as enabling progressive tax regimes and providing free healthcare for all.
Sarah Edwards, head of policy and campaigns at Health Poverty Action, said: "It is nothing less than shameful that the deaths of thousands of the world's most vulnerable women remain hidden and unaddressed through the failure to collect vital information about them.
"Many, many more could face the same fate, without decisive moves by the UK, other nations, institutions and non-governmental groups.
"We cannot stand back and let avoidable tragedies continue to cut short so many lives."