Oct. 2, 2006 When a patient complains of painful, swollen and stiff joints, the diagnosis is obvious: arthritis. But the physician may nevertheless have no idea what is causing the joint inflammation. A new diagnostic instrument can find the answer within two hours.
The cause of arthritis can often be sought way back in the past. Was it triggered by a bacterium? If so, by which of the at least eight known pathogens – Chlamydia or Salmonella, Borrelia or Campylobacter? Is there a virus involved, for instance Parvovirus B19? Or is the joint inflammation not due to an infection at all? Until now it has taken weeks of laboratory investigations to determine the exact cause of the complaint – and during this time the patient is often given the wrong treatment. In cooperation with the company of Mikrogen GmbH, the Fraunhofer Institute for Reliability and Microintegration IZM in Munich has devised a mobile laboratory system to remedy this situation. Housed in a case that is not much bigger than a shoe-box and will easily find room in any doctor’s practice, it consists primarily of a biochip, a black plastic wafer the size of a thumbnail, on which a hundred different antigen dots are printed. Each one of these 500-micrometer dots holds immobilized antigens of a possible arthritis pathogen.
The entire arthritis test can be carried out with only about half a milliliter of blood serum. “Our test system quickly indicates whether the patient has ever had any contact with one of these antigens,” explains Karl Neumeier of the IZM. The blood serum contains all the antibodies that the person’s immune system has ever produced. If an antibody from the blood finds its “own” antigen on the chip, it reacts accordingly. Fluorescent tagging makes this reaction visible. A reading device registers the fluorescent dots and identifies the respective antigen. If the test fails to produce a response, the cause is not an infection at all, but degeneration of the joint.
A wealth of microtechnology has been invested in this diagnosis principle, simple though it may appear. The biochip is housed in a cartridge the size of a credit card, in which all steps of the reaction take place successively. Microchannels and fluid distributors direct the chemicals to the exact spot where they are needed. The lab system is fast and efficient: it can process up to five cartridges from different patients at the same time within the space of only two hours. “The system has met with considerable interest, and we have already received concrete inquiries from would-be users,” reports Karl Neumeier. Once all the studies dictated by the German Medical Products Act have been completed, about two years from now, Mikrogen will start delivering the devices to doctors’ practices. The company is already working on a further test system for fast recognition of infections during pregnancy.
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