Take-home point: for new polyuria, think about whether it is APPROPRIATE (eg fluid shifts, including post-ATN or post-obstructive diuresis), or INAPPROPRIATE (particularly osmotic diuresis to glucose or mannitol; or diabetes insipidus, either central or nephrogenic). Also think about polydipsia!!
More PEARLS from the case:
- For DI: often will see Na>140
- For nephrogenic DI, some causes include hypercalcemia, hypokalemia, medications multiple myeloma
- For central DI, think about panhypopituitarism (including Sheehan’s!), subarachnoid hemorrhage
- For polydipsia, often see lower Na
- For work-up: primarily, water restriction + DDAVP while monitoring UOP and osms
- Corrects with water restriction = primary polydipsia
- Corrects with DDAVP = central DI
- Does not correct with either water restriction or DDAVP administration = nephrogenic DI
And thank you to Jake for bringing in a molecular medicine PEARL:
- FGF23: fibroblast growth factor 23: one of the first hormones that goes up in renal injury! It regulates systemic phosphate homeostasis, vitamin D metabolism, and more and could explain some of the complex endocrinopathies that happen with CKD.
- Here is a picture: http://www.nature.com/ki/journal/v77/n4/fig_tab/ki2009466f3.html