Take Home Point:
The major causes of hypophosphatemia include:
– increased cellular uptake (transcellular shifts)
– increased urinary excretion
– decreased intestinal absorption
The cause of hypophosphatemia can often be determined with a good history. However, when the etiology of hypophosphatemia is unclear, the next diagnostic step is to measure urinary phosphate excretion. This can be done with a 24-hour urine collection or a calculation of the fractional excretion of phosphate (FEPO4) from a random urine sample.
See the picture below for a full diagnostic algorithm.
Assadi F. Hypophosphatemia: An evidence-based problem-solving approach to clinical cases. Iranian Journal of Kidney Diseases. 2010;4:195-201.
Evernote Link: https://www.evernote.com/shard/s274/sh/52a92ae7-2b2c-42a4-891c-672d6eb3d5c6/6311ac2dffcd53637d9b4380f1ccbc47