Severe hyperglycemia with translocational hyponatremia
Marked hyperglycemia
Elevated serum osmolality
Common
Frequent causes
SIADH (E22.2)
Euvolemia on exam
Urine osmolality not maximally dilute
Thiazide associated hyponatremia (T50.2X1A)
Thiazide within 2 weeks
Older adult
Hypovolemic hyponatremia
Vomiting or diarrhea
Orthostatic symptoms
Hypervolemic hyponatremia
Heart failure (I50.9)
Cirrhosis (K74.60)
Nephrotic syndrome (N04.9)
Primary polydipsia
Excess water intake
Very dilute urine
Less common and mimics
Other etiologies
Hypothyroidism (E03.9)
Clinical hypothyroid features
Elevated TSH
Cerebral salt wasting
CNS injury context
Hypovolemia features
Reset osmostat
Stable mild hyponatremia
Appropriate urine dilution at lower set point
Pseudohyponatremia
Marked hyperlipidemia
Marked hyperproteinemia
Past Medical History
Conditions linked to hyponatremia
Endocrine
Adrenal insufficiency (E27.40)
Hypothyroidism (E03.9)
Cardiorenal hepatic
Heart failure (I50.9)
Cirrhosis (K74.60)
Chronic kidney disease (N18.9)
Neurologic and malignancy
Seizure disorder (G40.909)
CNS tumor (D49.6)
Small cell lung cancer (C34.90)
Recent hospitalization and procedures
Recent surgery
Recent ICU stay
Baseline function and supports
Functional baseline
Independent activities of daily living
Baseline gait aids
Living situation
Lives alone
Long term care
Physical Exam
General and vitals interpretation
Appearance
Toxic appearance
Somnolence
Agitation
Vital sign patterns
Fever
Hypotension
Tachycardia
Hypoxia
Neurologic
Mental status
Orientation deficits
Delirium features
Focal findings
Asymmetry
Aphasia
Severe findings
Active seizure
Posturing
Depressed respiratory drive
Volume status
Hypovolemia signs
Orthostatic hypotension
Dry mucous membranes
Delayed capillary refill
Reduced skin turgor
Hypervolemia signs
Peripheral edema
Elevated jugular venous pressure
Ascites
Pulmonary crackles
Euvolemia clues
No edema
No orthostasis
Cardiopulmonary and abdomen
Heart and lungs
New murmur
Crackles
Wheeze
Abdomen
Ascites
Hepatomegaly
Lab Studies
Core diagnostic labs
Serum studies
Basic metabolic panel
Serum osmolality
Glucose
Urea
Creatinine
Potassium
Urine studies
Urine osmolality
Urine sodium
Urinalysis
Endocrine screening when unclear
TSH
Morning cortisol
Other supportive tests
CBC
Liver enzymes
Interpretation framework
Tonicity classification
Hypotonic hyponatremia
Isotonic hyponatremia
Hypertonic hyponatremia
Severity by sodium
Mild 130 to 134 mmol/L
Moderate 125 to 129 mmol/L
Severe under 125 mmol/L
Urine osmolality pattern
Under 100 mOsm/kg suggests maximally dilute urine
100 mOsm/kg or higher suggests ADH effect
Urine sodium pattern
Under 30 mmol/L suggests low effective arterial volume
30 mmol/L or higher suggests SIADH or renal salt loss
Pseudohyponatremia check
Marked triglycerides
Marked paraproteinemia
Monitoring and safety labs during therapy
Sodium monitoring frequency
After each 3% sodium chloride bolus
Every 2 to 4 hours during active correction
Every 6 hours once stable in first 24 hours
Overcorrection mitigation monitoring
Urine output surge
Rising sodium faster than planned
Imaging
Scoring Systems
Neurologic severity tools
Glasgow Coma Scale
Eye response 1 to 4
Verbal response 1 to 5
Motor response 1 to 6
Delirium screen local protocol dependent
Acute onset or fluctuating course
Inattention
MRI
Brain MRI indications
Persistent focal deficit
Concern for CNS lesion with non diagnostic CT
MRI limitations
Time to scan
Metal implant contraindications
CT
CT head indications
New seizure
Focal neurologic deficit
Trauma
Severe headache
CT chest indications
Suspected malignancy driving SIADH
Unexplained SIADH with smoking history
Ultrasound
Volume assessment adjuncts
Lung ultrasound for pulmonary edema
IVC assessment local protocol dependent
Heart failure adjuncts
Focused cardiac ultrasound local protocol dependent
Pleural effusion assessment
Special Tests
Diagnostic maneuvers and bedside assessments
Orthostatic vitals
Supine to standing blood pressure change
Supine to standing heart rate change
Point of care glucose
Hypoglycemia exclusion
Hyperglycemia related hyponatremia context
Bladder scan and urine output tracking
Acute urinary retention as stress trigger
Polyuria after volume repletion risk for overcorrection
Etiology focused testing
Adrenal insufficiency evaluation
Random cortisol in shock
Cosyntropin stimulation test inpatient or outpatient planning
SIADH pattern confirmation
Low serum uric acid supportive
Fractional excretion of uric acid supportive local protocol dependent
ECG
Indications and patterns relevant to hyponatremia presentations
Indications
Syncope
Seizure like episode
Significant electrolyte abnormalities
Conduction and rhythm concerns
Bradyarrhythmia
Atrial fibrillation
Electrolyte related patterns
Hypokalemia associated U waves
QT prolongation risk with coexisting abnormalities
Assessment
Problem representation and severity
Hyponatremia syndrome (E87.1)
Symptom severity
Severe symptoms
Moderate symptoms
Mild or no symptoms
Chronicity estimate
Acute under 48 hours
Chronic 48 hours or longer
Tonicity
Hypotonic
Isotonic
Hypertonic
Volume status phenotype
Hypovolemic
Euvolemic
Hypervolemic
Etiology hypothesis with supporting data
Suspected SIADH (E22.2)
Euvolemia on exam
Urine osmolality not maximally dilute
Urine sodium 30 mmol/L or higher
Suspected hypovolemic hyponatremia
Orthostasis
Low urine sodium pattern
Suspected hypervolemic hyponatremia
Edema or ascites
Low urine sodium pattern in low effective arterial volume
Suspected adrenal insufficiency (E27.40)
Hypotension
Hyperkalemia pattern
Low cortisol pattern
Complications to prevent
Hyponatremic encephalopathy
Seizure risk
Cerebral edema risk
Osmotic demyelination syndrome risk
High risk host factors
Planned correction limits
Plan
First 5 minutes critical patient workflow
Immediate stabilization
Airway protection for coma or recurrent seizure
Oxygen for hypoxia
Cardiac monitor
Two large bore IV lines if unstable
Point of care glucose
Time critical targets
Sodium result as soon as available
CT head if seizure or focal deficit without delay
Immediate consult triggers
ICU for severe symptoms or 3% sodium chloride requirement
Nephrology for severe hyponatremia or complex correction
Endocrinology for suspected adrenal crisis or unclear endocrine driver
Hypertonic saline for symptomatic hypotonic hyponatremia
Indications for 3% sodium chloride
Seizure
Coma
Severe confusion
Signs of elevated intracranial pressure
Bolus strategy options guideline dependent
3% sodium chloride 100 mL IV over 10 minutes
Repeat up to 2 additional boluses for persistent severe symptoms
Alternative bolus strategy option guideline dependent
3% sodium chloride 150 mL IV over 20 minutes
Repeat 2 to 3 times as needed with sodium checks
Initial correction goal
Sodium rise 4 to 6 mmol/L
Symptom improvement
Monitoring during hypertonic therapy
Sodium after each bolus
Sodium every 2 to 4 hours during active correction
Avoiding overcorrection and relowering strategy
Correction limits
Target sodium rise 6 to 8 mmol/L max in 24 hours
Target sodium rise 18 mmol/L max in 48 hours
Desmopressin clamp strategy local protocol dependent
Desmopressin 2 mcg IV every 8 hours
Sodium checks every 2 to 4 hours
Overcorrection response
Stop hypertonic saline
Desmopressin 2 mcg IV once or repeat per protocol
Dextrose 5% water IV to relower sodium local protocol dependent
Etiology directed therapy after stabilization
Hypovolemic hyponatremia
Isotonic saline
Stop diuretics if appropriate
SIADH (E22.2)
Fluid restriction
Increase solute intake
Loop diuretic plus oral sodium chloride local protocol dependent
Identify and treat underlying trigger
Hypervolemic hyponatremia
Fluid restriction
Loop diuretics
Treat heart failure or cirrhosis drivers
Adrenal insufficiency suspected in shock
Hydrocortisone 100 mg IV now
Hydrocortisone 50 mg IV every 6 hours
Hypothyroidism related
Thyroid replacement planning inpatient or outpatient
Avoid attributing severe symptomatic hyponatremia solely to hypothyroidism
Do not do and common pitfalls
Unsafe actions
Hypotonic IV fluids in symptomatic hyponatremia
Rapid correction beyond limits
Pitfalls
Isotonic saline can worsen SIADH
Sudden water diuresis after volume repletion can overcorrect
Potassium repletion can raise sodium and contribute to overcorrection
Reassessment loop
Scheduled reassessment
Neuro check every 1 to 2 hours until stable
Strict intake and output
Repeat sodium every 2 to 4 hours during active correction
Escalation triggers
Worsening mental status
New seizure
Sodium rising faster than planned
Disposition
Level of care criteria
ICU
Seizure
Coma
Need for 3% sodium chloride boluses or infusion
Sodium under 120 mmol/L with moderate to severe symptoms
High risk for osmotic demyelination with active correction
Inpatient ward
Sodium under 125 mmol/L without severe symptoms but unclear cause
Need for frequent sodium monitoring
Persistent vomiting or poor intake
Suspected adrenal insufficiency or severe hypothyroidism
Observation pathway
Mild symptoms with improving trajectory
Reliable follow up and repeat sodium plan
Discharge
Mild hyponatremia 130 to 134 mmol/L
No neurologic symptoms
Clear reversible cause addressed
Reliable repeat sodium within 24 to 72 hours
Transfer considerations
Higher level monitoring
No ICU capability for hypertonic saline monitoring
Need for dialysis capability if complex renal failure and severe electrolyte derangements
Discharge Instructions
Copy discharge instructions
Diagnosis summary
Low blood sodium called hyponatremia
Symptoms can include nausea, headache, confusion, and in severe cases seizures
Medication plan
Stop offending medication if instructed
Avoid starting new diuretics unless prescribed
Fluid guidance
Follow the fluid limit provided by your clinician if fluid restriction recommended
Avoid large amounts of water or very dilute drinks until follow up
Follow up plan
Repeat blood test for sodium within 24 to 72 hours
Primary care or specialist follow up within 3 to 7 days
Return to emergency criteria
New or worsening confusion
Seizure
Fainting
Severe headache
Persistent vomiting
Trouble breathing
References
Guidelines and key reviews
Core guidance sources
European Society of Endocrinology clinical practice guideline on diagnosis and treatment of hyponatraemia 2014 Spasovski et al
US expert panel recommendations on diagnosis evaluation and treatment of hyponatremia 2013 Verbalis et al
American Family Physician review on sodium disorders 2023 Miller et al
Review of hypertonic saline strategies for hyponatremia 2021 Rondon-Berrios et al
CJASN perspective on treatment guidelines for hyponatremia 2024 Sterns
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.