1 47% of the global population has little to no access to diagnostics. 2 Diagnostics are central and fundamental to quality health care. This notion is underrecognised, leading to underfunding and inadequate resources at all levels. 3 The level of primary health care is the diagnostic so-called last mile and particularly affects poor, rural, and marginalised communities globally; appropriate access is essential for equity and social justice. 4 The COVID-19 pandemic has emphasised the crucial role of diagnostics in health care and that without access to diagnostics, delivery of universal health coverage, antimicrobial resistance mitigation, and pandemic preparedness cannot be achieved. 5 Innovations within the past 15 years in many areas (eg, in financing, technology, and workforce) can reduce the diagnostic gap, improve access, and democratise diagnostics to empower patients. 6 As an example of the potential impact, 1•1 million premature deaths in low-income and middle-income countries could be avoided annually by reducing the diagnostic gap for six priority conditions: diabetes, hypertension, HIV, and tuberculosis in the overall population, and hepatitis B virus infection and syphilis for pregnant women. 7 The economic case for such investment is strong. The median benefit-cost exceeds one for five of the six priority conditions in middle-income countries, and exceeds one for four of the six priority conditions in low-income countries, with a range of 1•4:1 to 24:1.Given the depth and breadth of the problems, sustained access to quality, affordable diagnostics will require multi-decade prioritisation, commitment, and investment.Incorporating diagnostics into universal health coverage packages will begin this process.