REASONING GP · Clinical algorithm · Quick reference

Hypernatraemia in adults — triage and diagnostic approach

Almost always a water problem, not a salt problem — and in community practice it is usually a frail older person who cannot get a drink. Ask why, and correct slowly.

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AdultsLab resultNa⁺ above 145v1.0 · Sep 2026

Core rule. Hypernatraemia is water deficit until proved otherwise, and it is a marker of dependency and illness severity, not just a number: mortality is high in the frail older patient, and the finding often means nobody has been giving them a drink. Na⁺ above 160 is an emergency whatever the patient looks like, and 155–160 with any neurological feature is too. Then two questions: why can this person not access or retain water — no access, impaired thirst, renal losses, GI losses, or a drug — and is there a safeguarding problem. Correct no faster than 0.5–1 mmol/L per hour, to a maximum of 10–12 mmol/L in 24 hours: too-rapid correction causes cerebral oedema and seizures.

On seeing the result: is this an emergency now? Arrange emergency admission — 999 or immediate discussion with the acute team

Na⁺ above 160 mmol/L, however well the patient seems · Na⁺ above 155 with any neurological feature, or any neurological feature at any level: confusion, drowsiness, reduced GCS, agitation, weakness, seizure, or a relative reporting the patient is "not themselves" · dehydration with hypotension or shock — systolic BP below 90, tachycardia, prolonged capillary refill, oliguria or anuria · unable to drink or swallow: vomiting, dysphagia, reduced consciousness, or no realistic means of oral intake at home · acute kidney injury with a rising creatinine · fever or suspected sepsis in a frail patient · capillary glucose above 11 mmol/L with dehydration (hyperosmolar hyperglycaemic state). Hand over the sodium with its previous values and dates, U&E, glucose, fluid and drug charts, and who normally provides the patient's drinks.

Grade it, then ask the only question that matters: why is this person not getting water? The cause is nearly always access, thirst or loss — and often all three

Grade by level

Above 160: emergency admission at any level of wellness. 155–160: emergency admission with any neurological feature, otherwise same-day assessment. 150–155 or any symptom: same-day, with admission if drinking is not possible. 146–149, alert and drinking: same-day or next-day review with a repeat. Symptoms and tempo override the number.

Can they get a drink?

The commonest cause in the community: frailty, dementia, immobility, stroke, dysphagia, being nil by mouth, depression, or simply no one bringing fluids. Ask who gives this person their drinks and how often — and whether the answer is nobody. In a care-home resident or dependent adult this may be neglect and a safeguarding matter.

Are they losing water?

Renal: osmotic diuresis from uncontrolled diabetes, diuretics, recovering AKI, obstruction relieved, hypercalcaemia, or diabetes insipidus — cranial (after head injury, surgery or pituitary disease) or nephrogenic (lithium, demeclocycline, chronic hypokalaemia). Extrarenal: vomiting, diarrhoea, high stoma output, fever, sweating, burns, tachypnoea.

Or gaining salt?

Much rarer, and usually iatrogenic: hypertonic saline or sodium bicarbonate, salt-rich feeds, sodium-containing effervescent or soluble preparations, hyperaldosteronism or Cushing's, and salt poisoning — which in a dependent adult or child raises safeguarding. Check the drug chart for sodium-containing preparations.

Red-flag screen: trigger → concern → destination → what to do before handover One row is enough; do not add up reassuring features

Trigger / red flag	Leading concern · destination	Do now · do not delay
Na⁺ above 160 mmol/L, however well the patient seems; or above 155 with any neurological feature; or any level with confusion, drowsiness, reduced GCS, agitation, weakness or seizure; or a rapid rise from a normal recent result.	Severe or acute hypernatraemia · cerebral dehydration Emergency admission now	These patients need controlled IV fluid with monitoring, not oral fluids and a repeat next week. Find and send the previous sodium values with their dates — tempo determines the safe correction rate. Symptoms, not the number, define severity: a confused patient at 150 needs admission while an alert one at 150 may not. Check capillary glucose to exclude a hyperosmolar state.
Dehydration with hypotension, shock or AKI: systolic BP below 90, tachycardia, prolonged capillary refill, oliguria, a rising creatinine, or a patient who cannot maintain any oral intake.	Hypovolaemic hypernatraemia · acute kidney injury Emergency admission now	Water and volume must be replaced together and intravenously. Hold nephrotoxics, NSAIDs, ACE inhibitors, ARBs, diuretics and metformin as appropriate and record what was held (NG148). Do not rely on encouraging oral fluids in a patient already hypotensive or oliguric. Add fever, vomiting, diarrhoea or high stoma output and there are two problems at once — sepsis assessment (NG51) plus an intake failure — and correcting one without the other fails.
Cannot drink or swallow: vomiting, dysphagia, reduced consciousness, nil by mouth, or no realistic means of oral intake at home — living alone without support, or a carer who cannot provide fluids.	Ongoing water deficit that cannot be corrected at home Admission now if the level is high or rising Same-day assessment and an urgent care plan	The management question is not the sodium but who will give the water. If nobody can, oral correction will fail whatever is prescribed, and the patient must be admitted or have same-day care arranged. New dysphagia needs a swallow assessment and its own diagnosis — including stroke.
Thirst, polyuria and a raised glucose: capillary glucose above 11 mmol/L with dehydration, weight loss or drowsiness, especially in type 2 diabetes or with new steroids.	Hyperosmolar hyperglycaemic state · osmotic diuresis 999 if drowsy, hypotensive or glucose very high Same-day assessment	Check capillary glucose and ketones in every dehydrated patient — HHS develops over days with profound dehydration and a high sodium, and the sodium here is a marker of severe fluid deficit, not a separate problem. Do not simply advise fluids and recheck; HHS carries a high mortality and needs hospital management.
Large-volume polyuria with normal glucose — passing dilute urine day and night with constant thirst; or hypernatraemia in a patient on lithium, or after head injury, pituitary surgery or with a known pituitary lesion.	Diabetes insipidus — cranial or nephrogenic Same-day advice if symptomatic or the sodium is rising; urgent endocrine investigation	Send paired serum and urine osmolality with a urine sodium, plus glucose, calcium, potassium and U&E. Dilute urine (low urine osmolality) in the face of a high serum osmolality is diabetes insipidus and needs endocrinology — a water deprivation test is a specialist procedure, never a primary-care one. Check the lithium level and renal function; nephrogenic DI from lithium may persist after stopping. Never restrict fluid in suspected DI.
Drug or iatrogenic cause: diuretics, lithium, demeclocycline, high-dose steroids, sodium-containing effervescent or soluble preparations, salt-rich enteral feeds, or hypertonic saline.	Drug-induced water loss or sodium load Same-day medication review; acute assessment if unwell	Reconcile the drug chart against the sodium trend, and include effervescent and soluble preparations, which carry a substantial sodium load. Hold or reduce the diuretic. Review lithium with mental-health input rather than stopping it unilaterally, and check the level. In enteral feeding, review the feed and free-water prescription with dietetics.
A frail, dependent or care-home patient with hypernatraemia — particularly if recurrent, or with pressure ulcers, weight loss, poor hygiene, unexplained injury, or a carer unable to explain the fluid intake.	Dehydration from neglect · unmet care need · possible salt poisoning Safeguarding adults referral — statutory duty, alongside the clinical route (Care Act 2014)	Hypernatraemia in a dependent adult is a recognised marker of neglect and carries a statutory safeguarding duty. Raise a safeguarding concern with the local authority in parallel with treating the patient — not instead of it, and not after waiting to see whether the sodium improves. Document who provides the fluids, the pattern of previous results, and the reason for the concern. Recurrent unexplained hypernatraemia in a dependent person requires this every time.

Trigger / red flag

Leading concern · destination

Do now · do not delay

Na⁺ above 160 mmol/L, however well the patient seems; or above 155 with any neurological feature; or any level with confusion, drowsiness, reduced GCS, agitation, weakness or seizure; or a rapid rise from a normal recent result.

Severe or acute hypernatraemia · cerebral dehydration
Emergency admission now

These patients need controlled IV fluid with monitoring, not oral fluids and a repeat next week. Find and send the previous sodium values with their dates — tempo determines the safe correction rate. Symptoms, not the number, define severity: a confused patient at 150 needs admission while an alert one at 150 may not. Check capillary glucose to exclude a hyperosmolar state.

Dehydration with hypotension, shock or AKI: systolic BP below 90, tachycardia, prolonged capillary refill, oliguria, a rising creatinine, or a patient who cannot maintain any oral intake.

Hypovolaemic hypernatraemia · acute kidney injury
Emergency admission now

Water and volume must be replaced together and intravenously. Hold nephrotoxics, NSAIDs, ACE inhibitors, ARBs, diuretics and metformin as appropriate and record what was held (NG148). Do not rely on encouraging oral fluids in a patient already hypotensive or oliguric. Add fever, vomiting, diarrhoea or high stoma output and there are two problems at once — sepsis assessment (NG51) plus an intake failure — and correcting one without the other fails.

Cannot drink or swallow: vomiting, dysphagia, reduced consciousness, nil by mouth, or no realistic means of oral intake at home — living alone without support, or a carer who cannot provide fluids.

Ongoing water deficit that cannot be corrected at home
Admission now if the level is high or rising Same-day assessment and an urgent care plan

The management question is not the sodium but who will give the water. If nobody can, oral correction will fail whatever is prescribed, and the patient must be admitted or have same-day care arranged. New dysphagia needs a swallow assessment and its own diagnosis — including stroke.

Thirst, polyuria and a raised glucose: capillary glucose above 11 mmol/L with dehydration, weight loss or drowsiness, especially in type 2 diabetes or with new steroids.

Hyperosmolar hyperglycaemic state · osmotic diuresis
999 if drowsy, hypotensive or glucose very high Same-day assessment

Check capillary glucose and ketones in every dehydrated patient — HHS develops over days with profound dehydration and a high sodium, and the sodium here is a marker of severe fluid deficit, not a separate problem. Do not simply advise fluids and recheck; HHS carries a high mortality and needs hospital management.

Large-volume polyuria with normal glucose — passing dilute urine day and night with constant thirst; or hypernatraemia in a patient on lithium, or after head injury, pituitary surgery or with a known pituitary lesion.

Diabetes insipidus — cranial or nephrogenic
Same-day advice if symptomatic or the sodium is rising; urgent endocrine investigation

Send paired serum and urine osmolality with a urine sodium, plus glucose, calcium, potassium and U&E. Dilute urine (low urine osmolality) in the face of a high serum osmolality is diabetes insipidus and needs endocrinology — a water deprivation test is a specialist procedure, never a primary-care one. Check the lithium level and renal function; nephrogenic DI from lithium may persist after stopping. Never restrict fluid in suspected DI.

Drug or iatrogenic cause: diuretics, lithium, demeclocycline, high-dose steroids, sodium-containing effervescent or soluble preparations, salt-rich enteral feeds, or hypertonic saline.

Drug-induced water loss or sodium load
Same-day medication review; acute assessment if unwell

Reconcile the drug chart against the sodium trend, and include effervescent and soluble preparations, which carry a substantial sodium load. Hold or reduce the diuretic. Review lithium with mental-health input rather than stopping it unilaterally, and check the level. In enteral feeding, review the feed and free-water prescription with dietetics.

A frail, dependent or care-home patient with hypernatraemia — particularly if recurrent, or with pressure ulcers, weight loss, poor hygiene, unexplained injury, or a carer unable to explain the fluid intake.

Dehydration from neglect · unmet care need · possible salt poisoning
Safeguarding adults referral — statutory duty, alongside the clinical route (Care Act 2014)

Hypernatraemia in a dependent adult is a recognised marker of neglect and carries a statutory safeguarding duty. Raise a safeguarding concern with the local authority in parallel with treating the patient — not instead of it, and not after waiting to see whether the sodium improves. Document who provides the fluids, the pattern of previous results, and the reason for the concern. Recurrent unexplained hypernatraemia in a dependent person requires this every time.

Safety rule. Correct no faster than 0.5–1 mmol/L per hour, maximum 10–12 mmol/L in 24 hours — rapid correction causes cerebral oedema and seizures, and the risk is greatest where the hypernatraemia is chronic. Never fluid-restrict a hypernatraemic patient, and never restrict fluid in suspected diabetes insipidus. Wellness is not reassurance above 160. And a sodium that is normal on treatment tells you nothing about whether the person can get a drink next week.

Colour is semantic: red = emergency now · amber = same-day assessment · blue = define/assess · green = primary-care management · purple = statutory duty or specialist route. Continued on page 2: assessment, classification, cause classifier, routine referral, primary-care management, endpoint.

REASONING GP · Hypernatraemia in adults — triage and diagnostic approach

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Assessment and investigation Hydration and cognition cannot be assessed remotely — and neither can whether anyone is providing fluids

Assess, and ask the question that decides the plan

GCS and orientation with a cognitive check where confusion is reported · lying and standing BP, pulse, mucous membranes, skin turgor, urine output · weight against previous · capillary glucose · temperature · swallow and speech · mobility and whether the patient can reach a drink unaided · pressure areas and general care. Then, recorded in the notes: who gives this person their drinks, and how often? — fluid intake over 24 hours, anyone else at home, whether the care package is being delivered, previous sodium results and dates, all drugs including effervescent and soluble preparations and enteral feeds, polyuria, vomiting, diarrhoea and stoma output.

Bloods and urine, then interpret

U&E with eGFR, glucose, calcium, potassium, albumin, FBC, CRP; paired serum and urine osmolality with a urine sodium where the cause is unclear. Concentrated urine (high osmolality): appropriate renal response — the problem is intake or extrarenal loss. Dilute urine with a high serum osmolality: diabetes insipidus or osmotic diuresis — check the glucose and calcium.

Classify: three exits, not two "Mildly raised, encourage fluids" is only safe when someone is actually providing them

Emergency or same-day

Above 160, above 155 with a neurological feature, shock or AKI, unable to drink, HHS, or 150–160. Output: destination, sodium with previous values and dates, hydration, glucose, drugs held, and who provides the fluids.

Mild, cause clear, manageable at home

Na⁺ 146–149, alert, drinking, no AKI, a reversible cause identified, and a named person who will provide the fluids. Output: cause, drug changed, fluid plan with a named provider, repeat date, escalation thresholds.

Unexplained, recurrent or safeguarding

Polyuria with dilute urine, hypernatraemia persisting despite fluids, a recurrent episode in a dependent adult, or lithium use. Output: state the uncertainty, take the §6 route — and raise safeguarding where the cause is unmet care need.

Cause classifier: intake, loss, or salt load Only once the urgency is settled

Inadequate intake
concentrated urine

By far the commonest cause in the community, and rarely the patient's choice: frailty, dementia, delirium, immobility, stroke, dysphagia, depression, being nil by mouth, or no one bringing drinks. Impaired thirst perception in the very old means dehydration occurs without any complaint of thirst. Recurrent episodes in a dependent adult are a safeguarding matter, not a fluid-advice problem.

Renal water loss
dilute or inappropriately dilute urine

Osmotic diuresis — uncontrolled diabetes (check glucose in everyone), relieved obstruction, recovering AKI, high-protein enteral feeds, mannitol · diuretics, especially loop diuretics in frailty · hypercalcaemia and chronic hypokalaemia, both of which impair concentrating ability · diabetes insipidus: cranial (head injury, pituitary surgery or disease) or nephrogenic (lithium, demeclocycline). Extrarenal loss — vomiting, diarrhoea, high stoma output, fever and sweating, tachypnoea, burns — is usually obvious, but only causes hypernatraemia when the losses are not matched by intake, so the intake question still applies.

Sodium gain

Much rarer and usually iatrogenic: hypertonic saline or sodium bicarbonate, salt-rich feeds, effervescent and soluble preparations (a frequently overlooked sodium load), hyperaldosteronism, Cushing's. Salt poisoning in a dependent adult or child is a safeguarding emergency.

Do not conclude by default

"Dehydration — encourage fluids" with no named person to provide them, in someone who could not reach a drink in the first place. "Mild, repeat in a month" without finding the previous results. "Poor intake" when the urine is dilute — that is renal loss and needs the osmolalities. Or a reversible cause accepted without checking glucose, calcium, potassium and the drug chart.

Refer routinely from this consultation Not same-day — the cases that leave by letter; §7 is what primary care does today

Suspected diabetes insipidus — polyuria with dilute urine against a high serum osmolality → endocrinology, with the paired osmolalities, glucose, calcium and potassium in the letter; a water deprivation test is specialist · nephrogenic DI on lithium → discuss jointly with mental health and nephrology, as renal impairment may persist after stopping · recurrent hypernatraemia in a dependent adult → safeguarding referral plus a care-needs reassessment, and a nursing or dietetic review of the fluid plan · new dysphagia → speech and language therapy, with stroke excluded first · enteral feeding → dietetics to review the feed and free-water prescription · frailty with repeated dehydration admissions → community frailty or geriatric service for an anticipatory care plan.

The only decisions that belong in this consultation What primary care manages today — mild hypernatraemia in an alert patient who can drink

Name who will provide the water — before anything else

A fluid plan with no named provider fails in exactly the patients who get hypernatraemia. Specify how much, how often, in what form, and by whom — patient, relative, carer visit or care-home fluid chart — and write it in the care plan. Hypodermoclysis or IV fluid is a nursing decision. If nobody can do it, this is not a primary-care plan. And correct slowly: no more than 0.5–1 mmol/L per hour, maximum 10–12 mmol/L in 24 hours, slower if chronic — too-rapid correction causes cerebral oedema and seizures — so measured amounts of water or oral rehydration solution across the day, never large boluses. Then the drugs and metabolic causes: hold or reduce the diuretic, stop effervescent and soluble preparations, review lithium with mental-health input and check the level, and check glucose, calcium, potassium and eGFR — uncontrolled diabetes, hypercalcaemia and hypokalaemia each cause renal water loss and are separately treatable.

Safeguarding — act in parallel, not afterwards

In a dependent adult, hypernatraemia is a recognised marker of neglect. Raise a safeguarding concern with the local authority at the same time as treating — not after waiting to see whether the sodium improves — and request a care-needs reassessment (Care Act 2014). Document the fluid history, who provides drinks, previous results and the basis of the concern. Recurrence requires this every time.

Recheck, the escalation rule, and what not to do

Recheck: U&E at 24–48 hours (sooner if above 150), then until normal and stable, with the triggers written down and told to the carer — any confusion, drowsiness, seizure or inability to drink, or Na⁺ above 160 → emergency admission; 150–160, or no improvement at 48 hours → same-day assessment. Do not: fluid-restrict · correct rapidly · "encourage oral fluids" in someone who cannot reach, hold or swallow a drink · accept "poor intake" when the urine is dilute · restrict fluid in suspected diabetes insipidus · omit the glucose · or file a sodium of 149 in a care-home resident with no plan, no named fluid provider and no safeguarding thought.

Endpoint and documentation Finish with one of four conclusions

1 · Emergency

Admission arranged; sodium with previous values and dates, GCS, hydration, BP, glucose, U&E, drugs held, and who provides the fluids.

2 · Same-day

Assessment today; hydration and cognition recorded; glucose checked; osmolalities sent if the cause is unclear; diuretic held; repeat in 24–48 h.

3 · Mild, managed at home

Level, cause and previous results recorded; fluid plan with a named provider and volume; drugs reconciled; repeat date and thresholds given to the carer.

4 · Unexplained or safeguarding

Uncertainty stated; §6 referral sent with the osmolalities; safeguarding concern raised and logged; care-needs reassessment requested; review owner.

Why primary-care management is safe today, in one line: Na⁺ is 146–149 · alert, no confusion or drowsiness · able to drink, and a named person will provide measured fluids · BP and pulse normal, passing urine · glucose, calcium, potassium and eGFR checked · previous results found, the rise not rapid · drugs reconciled · safeguarding considered and raised where indicated · repeat at 24–48 hours with a named reviewer and written thresholds. Safety-net, for patient and carer: contact us or 111 the same day if they become confused or unusually sleepy, stop drinking, start vomiting, or pass much less urine; call 999 for a fit or collapse.

Remote and result-handling limitation. Hydration, cognition and whether anyone is actually giving this person a drink cannot be assessed on the telephone — a sodium above 149, or reported confusion, needs a face-to-face visit. Convert to face-to-face or emergency assessment where the patient lives alone or depends on carers, a relative reports drowsiness or reduced drinking, there is vomiting or dysphagia, or the episode is recurrent.

Clinical decision support only; follow local acute-transfer, renal, safeguarding and prescribing policies and check doses against the current BNF. Source hierarchy: NICE guidelines and CKS first, then BNF/MHRA for doses and safety, then national specialty guidance. Sources: NICE CG174 Intravenous fluid therapy in adults in hospital · NG148 Acute kidney injury · NG203 Chronic kidney disease · NG28 Type 2 diabetes in adults · NG51 Sepsis · NG108 Decision-making and mental capacity · CG103 Delirium · NICE CKS Hypernatraemia, Dehydration, Diabetes insipidus, Safeguarding adults · Care Act 2014 safeguarding duties · Society for Endocrinology guidance on diabetes insipidus (arginine vasopressin deficiency) · UK Kidney Association · BNF · MHRA. Review after any guidance or medicines-safety update, otherwise every 6 months. © Reasoning GP · gpreasoning.uk