Tuesday, 19 August 2014
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How does one interpret the following lab values in a patient with hyponatremia.

Serum Na : 104 meq/l
Serum K : 3.1 meq/l
GRBS :90 mg/dl
serum osmolality : 236 mosmol/kg
urine osmolality : 117 mosmol/kg
Urine Na : 12 meq/l
Urine K : 9 meq/l

Serum creat : 0.3 mg/dl
BUN : 5 mg/dl
Uric acid : 0.5 mg/dl
TSH and random cortisol : normal


Most of the values would well with SIADH except for urine Na and K which suggest volume depletion. Can they co-exist ? Clinically the patient appears dehydrated but not severely so. Treating with adequate hydration (normal saline) and 3% saline has brought up the Sodium to 120 over 2 days.
Sorry for the late reply. We had some technical difficulties with recent questions.

The urine is relatively dilute to invoke SIADH. If SIADH were present, one would expect a significantly higher urine osmolality. The presence of volume contraction will complicate a diagnosis of SIADH since the kidney might be sodium avid. In SIADH, if patients are not volume contracted, the urine sodium is often much higher than in your case.

It its possible the patient became volume contracted but with volume resuscitation, inhibited ADH and led to the water diuresis you are seeing here. Perhaps the higher osmolality in urine preceded the testing you did. But to answer your question, SIADH does not seem likely.

Dr. Jordan Weinstein
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