Urine Test Detects Changes in Bone Mineral Balance

An innovative technique has been introduced that is more sensitive in detecting bone loss than the X-ray method used today, and with less risk to patients.

With the novel technique, bone loss is detected by carefully analyzing the isotopes of the chemical element calcium that are naturally present in urine and eventually it may find use in clinical settings, and could pave the way for additional innovative biosignatures to detect disease.

The technique makes use of a fact that has been exploited by scientists at Arizona State University (ASU; Tempe, AZ, USA), but seldom used in biomedicine. This is that different isotopes of a chemical element can react at slightly different rates. When bones form, the lighter isotopes of calcium enter bone a little faster than the heavier isotopes. That difference, called isotope fractionation, is the key. Isotope abundances were measured by multiple-collector inductively coupled plasma mass spectrometry (ICP-MS, Thermo Scientific; Waltham, MA, USA).

Patients do not need to ingest any artificial tracers and are not exposed to any radiation, so there is virtually no risk to them. The study examined calcium isotopes in the urine of a dozen healthy subjects confined to bed for 30 days. Whenever a person lies down, the weight-bearing bones of the body, such as those in the spine and leg, are relieved of their burden, a condition known as "skeletal unloading.” With skeletal unloading, bones start to deteriorate due to increased destruction. Extended periods of bed rest induce bone loss similar to that experienced by osteoporosis patients, and astronauts.

Urine samples were collected at time points throughout the study to examine short-term variations in calcium isotope abundances either from analyses of 24-h pooled samples or in some cases, on all individual voids throughout the day. Laboratory analysis of the subjects’ urine samples revealed that the technique can detect bone loss after as little as one week of bed rest, long before changes in bone density are detectable by the conventional approach, dual-energy X-ray absorptiometry (DEXA). Importantly, it is the only method, other than DEXA, that directly measures net bone loss.

Anna Barker, PhD, director of Transformative Healthcare Networks at ASU, said, "The concept of inorganic signatures represents a new and exciting approach to diagnosing, treating, and monitoring complex diseases such as cancer. There is an opportunity to create an entirely new generation of diagnostics for cancer and other diseases." The study was published on May 31, 2012, in the Proceedings of the National Academy of Science of the United States (PNAS).

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Arizona State University
Thermo Scientific