The test kits are provided in developing countries like Zambia for free distribution, the U.S. Agency for International Development's (USAID) Office of Inspector General (OIG) said.
It said the arrests stem from an effort to make U.S. foreign assistance more effective and accountable by investigating complaints of fraud and misconduct in global health programs.
'We coordinate closely with international partners to thwart the work of criminals who prey upon the U.S. government-supported global health supply chain,' said Jonathan Schofield, OIG's special agent in charge of global health investigations.
'Our recent work with partners in the U.S. Embassy in Zambia and Zambia National Task Force has stopped several offenders who exploited international aid for personal gain,' he said in a statement.
The six people were arrested in Zambia last week on suspicion of illicitly selling the medical kits in its capital, Lusaka.
During a five-month probe, investigators visited pharmacies in Lusaka and found kits on sale that had been provided by the U.S. government and the Global Fund to Fight AIDS, Tuberculosis and Malaria, a public-private partnership, OIG said.
The six people arrested were the main targets of the investigation and remain in jail, it said.
Earlier OIG investigations have rooted out the illegal sale of anti-malarial drugs in Guinea and Malawi, it said.