Smart phone for diagnosing kidney disease

A smart phone has been adapted to measure levels of albumin in urine as a way to detect kidney disease. It follows on from recent reports in which a smart phone was transformed into a spectrometer and another was used for testing soils for TNT. The new application, described in Lab on a Chip by scientists from UCLA, relies on measuring a fluorescent signal which is directed towards the phone's camera.

The tester unit weighs in at just 148 g and is easily fitted to the phone. A small volume of urine is transferred to a tube inside the device where it mixes with a dye that is sensitive to albumin, Upon illumination by an inexpensive battery-powered laser diode operating at 532 nm and 5 mW, an android app measures the fluorescence signal and converts it to an absolute concentration of albumin, based on a calibration using a known amount of albumin in a control tube which is also illuminated.

The actual measurement is displayed within 1 second and typical sample preparation takes 5 minutes, so the whole test can be conducted quickly, possibly at the patient's side to provide real point-of-care testing. The app is programmed to display individual measurements but can also display daily or weekly reports to follow fluctuations in albumin levels.

Albumin is generally present in urine at levels below 30 µg/mL but kidney damage tends to release more of the protein to levels up to 300 µg/mL. The detection limit of this device is 5-10 µg/mL, so it is well below the "normal" clinical range. It would be possible to conduct more than one test, so that creatinine could be measured in parallel to provide the albumin/creatinine ratio, which is a conventional means of comparing samples.

Despite the success of this device, the research team are aware of the practical difficulties that will occur due to rapidly changing phone technology. It might be difficult to keep up with new developments to allow the device to continue to function on new phones as they are released. This will be a challenge to the developers of many types of scientific apps for smart phones.