28 May 2012 Last updated at 21:14 ET By Michelle Roberts Health editor, BBC News online

Nasa scientists believe they have found a way to spot osteoporosis bone loss at the earliest disease stages.

Currently, the condition can go undetected for years and may only be diagnosed with scans after weakening of the bones has led to a fracture.

The new test - designed partly with astronauts in mind as they too can suffer bone loss due to the microgravity of space - looks for traces of bone calcium in the urine.

The work is published in PNAS journal.

The technique developed by scientists at Arizona State University working with the US space agency analyses calcium isotopes - different atoms of the element calcium, derived from bone and each with their own specific number of neutrons.

This could therefore have a future role in the clinical evaluation of patients

The balance or abundance of these different isotopes changes when bone is destroyed and formed and can therefore indicate early changes in bone density.

To put it to the test, the researchers studied a dozen healthy volunteers whom they confined to bed rest for 30 days. Prolonged bed rest triggers bone loss.

The technique was able to detect bone loss after as little as one week of bed rest - long before changes in bone density would be detectable on conventional medical scans such as dual-energy X-ray absorptiometry (DXA).

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'Nasa test' spots early bone loss