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Table 2 Summary of recommendations for approaches to diagnosis of hyponatremia by included guidance documents

From: Diagnosis and treatment of hyponatremia: a systematic review of clinical practice guidelines and consensus statements

  Guideline Organization/Society  
Criteria/Categories NIV [16] NHS [17] GAIN [22] AEEH [23] EHN [25] ERBP/ESE/ESICM [20] UF [18] HEP [19] RCHM [21] EAH-ICD [24]
Threshold workup [Na] <135 mmol/L <135 mmol/L <135 mmol/L <130 mmol/L <135 mmol/L <135 mmol/L <131 mmol/L <135 mmol/L <135 mmol/L  
Confirming hypotonic hyponatremia Serum osmolality <275 mOsm/kg Plasma osmolality <280 mOsm/kg Serum osmolality <275 mOsm/kg   Plasma osmolality <275 mOsm/kg Serum osmolality <275 mOsm/kg Serum osmolality <285 mOsm/kg Plasma osmolality <280 mOsm/kg Serum osmolality threshold not stated  
How to classify hypotonic hyponatremia to aid identification of underlying cause           
Volume status/hydration state/extracellular fluid status Clinical evaluation Physical examination/clinical signs of dehydration or edema Physical examination/clinical signs of dehydration or edema   Physical examination/clinical signs of low circulating volume Physical examination/clinical signs of dehydration or edema Physical examination/laboratory measurements Physical examination/laboratory measurements To assess but method not stated  
Urinary [Na]/Threshold 30 mmol/L Spot urine: 20–30 mmol/L 15 mmol/L   40 mmol/L 30 mmol/L 25 mmol/L Spot urine: 20–30 mmol/L No threshold stated  
Urinary osmolality/Threshold 100 mOsm/kg 100 mOsm/kg 100 mOsm/kg   100 mOsm/kg 100 mOsm/kg 100 mOsm/kg 100 mOsm/kg No threshold stated  
How to identify the underlying disorder           
History   Medications Medications    Diuretic use     
   Fluid intake Recently prescribed intravenous fluids        
   Nocturnal polyuria Vomiting/diarrhea        
Lab tests           
Serum potassium concentration + +        +  
Serum chloride concentration   +        +  
Serum urea concentration +/– +      +/– +/– +  
Serum creatinine concentration + +      +/– +/– +  
Serum glucose concentration + + +/–    +    +  
Urinary potassium concentration +       +    
Renal tests    +        
Liver tests    +     +/–    
Urinary protein   +/–         
Thyroid function tests +/– +/– +/–     +/–    
Adrenal function tests +/– +/– +/–     +/–    
Serum protein electrophoresis   +/–         
Urine protein electrophoresis   +/–         
Fractional sodium excretion +/–          
Serum uric acid concentration +/– +/–      + +/–   
Fractional uric acid concentration +/–          
Fractional excretion urea +/–          
Urinary chloride concentration +/–       + +/–   
Molar weight urine +/–          
Serum bicarbonate concentration        +/–    
Hematocrit        +/–    
  1. [Na], Serum sodium concentration; +, always; +/–, If clinically indicated/sometimes useful.
  2. NIV, Nederlandse Internisten Vereniging [16]; NHS, National Health Service [17]; GAIN, Guidelines and Audit Implementation Network [22]; AEEH, La Asociación Española para el Estudio del Hígado [23]; EHN, European Hyponatremia Network [25]; ERBP, European Renal Best Practice; ESE, European Society of Endocrinology; ESICM, European Society of Intensive Care Medicine [20]; UF, University of Florida [18]; HEP, Hyponatremia Expert Panel [19]; RCH Melbourne, the Royal Children’s Hospital Melbourne [21]; EAH-ICD, International Exercise-Associated Hyponatremia Consensus Development Conference [24].