Up to 300,000 patients using anti-blood clotting drugs may soon be able to test how their therapy is working at home.

Trials of home-testing kits, sponsored by the government, are yielding promising results. Doctors, patients and manufacturers hope the handheld machines, priced at £399, could soon be as common as blood sugar monitors used by people with diabetes.

The devices hold out the prospect of fewer visits to outpatient clinics and more efficient use of NHS services. The technology has been available for some years - 3,500 Britons use it already.

Patients prick their fingers and place a spot of blood on a test strip, which then passes into the machine. This provides a digital readout of their blood thickness levels.

Officials are seeking to establish how the self-testing procedure compares with traditional checks after ministers' pledges to give patients with chronic conditions more control over their treatment.