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What exactly is SIADH?

SIADH stands for the Syndrome of Inappropriate Anti-Diuretic Hormone secretion. 

What that means is your body is secreting an excess of the hormone that causes a concentrated urine. 

This concentrated urine will in turn not allow the body to excrete excess water taken in. 

When one cannot excrete excess water, water accumulates in the body and dilutes the blood sodium level to below normal levels. The normal serum sodium is typically 135-145 meq/L. 

With SIADH and fluid intake the serum sodium gets diluted; typically below the 135 meq/L mark and usually a lot lower than that. Starting at even mildly low serum sodium levels symptoms start to develop 

Symptoms of Hyponatremia include: 

  • Headache
  • Nausea 
  • Brain Fog 
  • Memory impairment 
  • Instability with walking
  • Concentration difficulty
  • Lethargy 
  • Weakened bones 
  • Falls 
  • Fractures
  • Seizures 
  • Increase mortality

How is SIADH diagnosed? 

SIADH starts with a volume exam. This is tricky even for Nephrologists. In essence with SIADH you are retaining water, not salt so the exam is fairly benign. Typically patients will not have significant swelling, weight gain, shortness of breath, low blood pressure, or jugular vein distention. 

If your practitioner feels the exam is what we call euvolemic (not wet or dry), then we look at the Urine and Blood.  

Urine in SIADH: 

  1. Urine Sodium is high, usually above 30 meq/L.
  2. Urine Osmolarity (concentration) is high typically above 300 but at least above 100 meq/L. 

Blood in SIADH:

  1. Serum Sodium is low, usually under 134 meq/L
  2. Serum Osmolarity is low, usually under 275 meq/L
  3. Uric acid is low, usually under 4 mg/dl 
  4. Thyroid and Adrenal testing are in the normal range 
  5. Normal kidney function with BUN often under 10 mg/dl 

With all of those factors in place you may have SIADH. 

Now the question is What is causing SIADH? 

While there are many possibilities the most common reasons for SIADH are below.  

Medications may be the culprit, you can read more on that here 

Brain or Lung pathologies  

More on that here 


Short term, after surgery from pain or nausea

Sometimes however, your doctor may not know exactly what is causing the SIADH.

That is termed idiopathic. 

Once the diagnosis is established, no matter what the reason, we must figure out how to treat the condition. 

How the experts treat SIADH, based on the European best practice guidelines

The first line of treatment is a proper fluid restriction. This is typically 1 liter or less of all liquids per day. This is often coupled with a modest salt and high protein intake. 

Second line treatments include UreaAide™ Urea powder or furosemide plus salt tablets, usually coupled with potassium and magnesium supplements. Most nephrologists agree, Urea is superior based on recent evidence showing the furosemide salt strategy led to more kidney issues and low potassium levels. 

Third line treatments are the Vaptans. These are water pills in the true sense of the word. They are costly at about 300 USD a pill. In America they are only covered in short duration and only after a hospitalization. They have a lot of side effects including excessive thirst, dry mouth, excessive urination (especially at night), too rapid correction (which can be dangerous) and liver toxicity. 

In closing. 

SIADH is inappropriately concentrated urine leading to a dilution effect on blood sodium. SIADH etiologies are wide reaching including medications, malignancies, lung and brain pathologies as well as idiopathic. Lastly the treatments for SIADH are varied with a cornerstone of fluid restriction often coupled with Urea. 

Dr. Barry 


Board Certified Nephrology and Internal Medicine