1. Hyponatremia and Sodium HandlingBy
Brent Lee Lechner, DO
MAJ, MC, USA

2. Basic Concepts in Urine Evaluation
U Na+ reflects renal perfusion independent of S Na+:
Low U Na+ (<10 to 20 mEq/L)
Renal Perfusion is decreased
Possible Tubular defect
High U Na+ (>20 mEq/L)
Renal Perfusion is increased or normal
Defect in tubule reabsorption
So: If U Na+ elevated in clinical circumstance when renal blood flow is expected : Identify renal reabsorption defective.

3. Basic Concepts in Urine Evaluation
U OSM reflects H20 removal from tubule fluid:
Normal U OSM ( mOsm/L)
SG in urine = U OSM 300mOm/L
U OSM > 1.5 X S OSM: ADH must be acting on collecting duct – irrespective of S OSM
Physiologic stimuli for ADH release
Increase S OSM/ S Na+
Decrease intravascular volume
If U OSM/S OSM > 1.5 without increased S OSM or decreased intravascular volume – ADH secretion is non-physiologic – irrespective of urine volume.

4. Clinical Utilization of U Na and U OSM
Increased Weight U Na U OSM Decreased Weight
Hypoalbuminema <10 > Dehydration/Volume Depletion
Nephrosis/Cirrhosis Cystic Fibrosis
AGN
Acute Volume expansion <10 < Diabetes Insipidus
Water Intoxication
Excess IV Fluid
Acute Renal Failure >50 <= Adrenal Insufficiency
Sepsis,Shock, Nephrotoxin Salt-losing Nephropathy
Interstitial Npehritis/Cystic Dz/
Urinary Tract Obstruction
Non-Physiologic ADH >50 > DKA
Osmotic Diuretics

5. Case Series Serum Urine
Change in Weight Na K Osm Glucose BUN/Cr Na Osm
Decreased / <
Decreased /
Increased / <
Decreased /
Increased /
Decreased /