Independent tests on two batches of the kits were performed by the MHRA Medical Evaluation Centre in Guildford and confirmed that the sensitivity of the kit was inadequate to identify early pregnancy. 26,380 kits distributed to 29 UK healthcare organisations including GP surgeries, health clinics and hospitals since 1st October are being withdrawn by the UK distributor and NHS Direct have recommended that women who have had a negative pregnancy test performed between mid-November 2003 and March 2004 make an appointment with their GP or consultant. Test kits for home use are not affected by this warning and no other pregnancy test kit is known to be affected. Pregnancy tests work by measuring HCG (Human Chorionic Gonadotrophin), a hormone that is produced in very large quantities during pregnancy. The test is normally performed on urine using a test kit but blood tests with high sensitivity are sometime used and performed in hospital laboratories. Both urine and blood tests use a method called immunoassay, which uses the properties of antibodies to bind to the specific chemicals of interest. With the SAS One-Step test, the development of a line on the test device suggests the women is not pregnant, the absence of a line suggests pregnancy. These test kits are not 100% accurate, they are generally designed to be positive in urine from women who are 2 or more weeks pregnant. The results become more reliable as the pregnancy progresses and the urine HCG concentration increases. Urine pregnancy tests are performed in the healthcare sector to confirm pregnancy and to exclude it before giving treatment/drugs/x-rays. The MHRA is an Executive Agency of the Department of Health which has responsibility for safeguarding public health and patient safety by ensuring that medical devices, medicines and other healthcare products meet the appropriate standards of safety, quality and performance. Where significant defects or deficiencies are identified it issues Medical Device Alerts to the NHS and hospitals in the independent sector. It also supports a number of UK evaluation centres, which test the quality and performance of medical devices.