They believe blood serum contains chemicals which stops the build-up of nanobacteria, but that they can be transported to the kidneys by the blood where they may build up. They are looking into whether nanobacteria could be behind other diseases, such as gallstones. Som scientists believe there may have been similar nanobacteria on Mars, but there are conflicting views. Those backing the nanobacteria theory say fossils have been found in meteorites on the surface of Mars which suggests their presence. The fossils suggest organisms of the same shape and size as the nanobacteria found in human blood.
Kidney stones can cause severe pain.
Sometimes blood can appear in the urine. Many will be passed without medical assistance, but in some cases, operations are required to remove them. The BBC is not responsible for the content of external internet sites.