There are a number of ways to grade the severity of SIADH. The most obvious is to look at how low the sodium is. The problem with this is that it largely depends on how much water a patient is drinking and is not solely dependent on the severity of the SIADH. A patient with mild SIADH that is started on hypotonic fluids will have a much lower sodium than a patient with severe hyponatremia who is adherent with her water restriction and urea tablets.
I assess the severity of SIADH by looking at the electrolyte content of the urine. Here is a doozy:
- Urine sodium: 134
- Urine Potassium: 62
- Urine osmolality: 777