EPISODE · Feb 23, 2026 · 23 MIN
The SIADH Trap: Diagnosis, Causes, and the Mimics That Will Fool You
from NephBytes · host Dr Amit Kaushal
You've checked the osmolality. It's low. The patient looks euvolemic, the urine is concentrated, the urine sodium is high. It looks like SIADH — and you're ready to make the diagnosis.Not so fast.SIADH is a diagnosis of exclusion. In this episode, we build a precise picture of what SIADH actually is — and why calling it a sodium problem instead of a water problem is the first mistake most people make. We go through the drug causes you need to know, including a detailed case of cyclophosphamide-induced SIADH in a patient with GPA where the bladder hydration protocol turns a drug side effect into a crisis.Then we go deep on the three mimics that wear SIADH's face. Adrenal insufficiency — the one you cannot afford to miss, with no hyperkalemia to tip you off in the secondary form. Hypothyroidism — the nuance of when it actually causes hyponatremia versus when a mildly elevated TSH is a red herring. And reset osmostat — the diagnosis that requires no treatment and where treating is futile.We close with the fracture data — why a sodium of 131 in your clinic patient is not something to watch and wait.Next episode: SIADH treatment — 3% saline bolus strategy, the desmopressin clamp, rescuing overcorrection, and subarachnoid hemorrhage where the rules change entirely.
What this episode covers
You've checked the osmolality. It's low. The patient looks euvolemic, the urine is concentrated, the urine sodium is high. It looks like SIADH — and you're ready to make the diagnosis.Not so fast.SIADH is a diagnosis of exclusion. In this episode, we build a precise picture of what SIADH actually is — and why calling it a sodium problem instead of a water problem is the first mistake most people make. We go through the drug causes you need to know, including a detailed case of cyclophosphamide-induced SIADH in a patient with GPA where the bladder hydration protocol turns a drug side effect into a crisis.Then we go deep on the three mimics that wear SIADH's face. Adrenal insufficiency — the one you cannot afford to miss, with no hyperkalemia to tip you off in the secondary form. Hypothyroidism — the nuance of when it actually causes hyponatremia versus when a mildly elevated TSH is a red herring. And reset osmostat — the diagnosis that requires no treatment and where treating is futile.We close with the fracture data — why a sodium of 131 in your clinic patient is not something to watch and wait.Next episode: SIADH treatment — 3% saline bolus strategy, the desmopressin clamp, rescuing overcorrection, and subarachnoid hemorrhage where the rules change entirely.
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The SIADH Trap: Diagnosis, Causes, and the Mimics That Will Fool You
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