Tests for Lyme disease are so poor that they can miss up to half of all cases.  Even test kits that have been approved by drug regulators such as the Centers for Disease Control in the US miss an average of 88 cases out of every 200.
Current testing kits are no better than tossing a coin, says the Lyme and Associated Diseases Society, and, as a result, many people with the disease are walking around undiagnosed.
(Source: British Medical Journal, 2007; 335: 1008).