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NOTTINGHAM UNIVERSITY HOSPITAL NHS TRUST: Clinical Chemistry Guidelines
Hyponatraemia Guideline
Document Information
Policy Reference: Hyponatraemia Guideline Issue: 1: Version 3
Author Job Title:
Peter Prinsloo Consultant Chemical Pathologist
STATUS: FINAL
First Issued On:
June 2000
Latest Reissue Date:
March 2008
Document Derivation:
See references
Ratified By:
Department of Clinical Pathology
Review Date:
March 2010
(or sooner if necessary)
Consultation Process:
Reviewed in the Department of Clinical
Chemistry
Distribution:
Clinical Pathology Website
Change record
Date Author Description Change
Record
June 2000
Peter Prinsloo
Nigel Lawson
New Policy Version 1
August 2005 Peter Prinsloo Reviewed with minor word
changes
March 2008 Peter Prinsloo Reviewed with minor word
changes
Version 2
Version 3
Created on 14/03/2008 Page 1 of 4

NOTTINGHAM UNIVERSITY HOSPITAL NHS TRUST: Clinical Chemistry Guidelines
Hyponatraemia Guideline
Definition
Sodium less than 135mmol/L. Hyponatraemia is usually only clinically significant if
sodium concentration is less than 125mmol/L or there is a rapid drop in sodium
concentration (> 20mmol/L in 24 h). Investigate for hyponatraemia if sodium is
persistently less than 130mmo/L.
Symptoms/Signs
Nausea
Vomiting
Headache
Confusion
Hypotension
Seizures
Coma
Common Causes
Inappropriate IV fluids e.g. dextrose
Oedematous states e.g. liver failure, congestive cardiac failure, nephrotic
syndrome and myxoedema.
Diuretics
Hyperglycaemia (appropriate osmotic response)
Fluid loss (hypertonic dehydration)
Mineralocorticoid deficiency
SIADH (see below)
Please note this list is not comprehensive and other causes may need to be considered.
Artefacts
Sample taken from drip arm
Gross lipaemia (measure plasma lipids)
Gross hyperproteinaemia (measure total protein)
N.B. Ward-based sodium meters (blood gas analysers) are not affected by lipid or protein.
Created on 14/03/2008 Page 2 of 4

NOTTINGHAM UNIVERSITY HOSPITAL NHS TRUST: Clinical Chemistry Guidelines
Clinical Assessment
Before carrying out extensive investigations clinically assess the patient
• Fluid status- dehydration, euvolaemia, oedema
• Accurate fluid balance charts and weight.
Initial Investigations
Plasma
- Sodium, Potassium, Urea, Creatinine
- Glucose
- Osmolality
- Liver function tests
- Thyroid function tests
Urine (random, no preservative)
- Sodium, Creatinine
- Osmolality
Further Investigations
(If common causes excluded)
In a clinically dehydrated patient
- If the urinary sodium is high (>20mmol/L) then renal loss of sodium is the most
likely cause. Consider adrenocortical insufficiency.
- If the urinary sodium concentration is low (25-30mmol/L) consider SIADH
- If the urinary osmolality is inappropriately high then consider SIADH
Created on 14/03/2008 Page 3 of 4

NOTTINGHAM UNIVERSITY HOSPITAL NHS TRUST: Clinical Chemistry Guidelines
Diagnostic Criteria for Syndrome of Inappropriate ADH (SIADH)
The diagnosis of SIADH is a diagnosis of exclusion.
The following criteria must be met
- Plasma Na < 135mmol/L
- Plasma osmolality < 270mOsmol/kg
- Urine osmolality > 100mOsmol/kg
- Urine Na > 25-30mmol/L
- No clinical evidence of hypovolaemia or oedema/ascites
- Normal adrenal, thyroid, pituitary and renal function
- Not on diuretic therapy
References
1) Sodium. Kumar S, Berl T. The Lancet 1998; 352: 220-229.
2) The Hyponatraemic patient: Practical focus on therapy. Lauriat SM, Berl T. J Am Soc of
Nephrology 1997; 8: 1599-1607.
Disclaimer: These guidelines have been registered with the Trust. However, clinical
guidelines are guidelines only. The interpretation and application of the clinical guidelines will
remain the responsibility of the individual clinician. If in doubt contact a senior colleague or
expert. Caution is advised when using guidelines after the review date.
Created on 14/03/2008 Page 4 of 4