See also

Key points

1. Children with suspected or known diabetes insipidus (DI) must always have free access to water. Never restrict fluid intake
2. Urine output may not reflect hydration status
3. Close monitoring of electrolytes and fluid balance is required for inpatients with DI. This is particularly critical when children are too young or too unwell to adequately respond to thirst
4. Beyond emergency resuscitation, sodium chloride containing fluids should never be given to children with nephrogenic DI without specialist consultation

Background

• DI is an uncommon condition with either reduced or absent secretion of anti-diuretic hormone (ADH) from the hypothalamus, or insensitivity to ADH within the kidney
• This leads to an inability to concentrate urine causing polyuria with compensatory polydipsia and potentially fluid and electrolyte imbalance
• Causes:
• central: head trauma, brain tumour in/near the pituitary, post-neurosurgery, genetic, meningitis or idiopathic
• nephrogenic: genetic or acquired urinary concentrating defects
• systemic or drug-related causes are rare
• DI is dangerous when a child is unable to access water freely (eg very young child, altered conscious state, nil by mouth or too unwell) or has an impaired thirst response (eg complex midline CNS defect, hypothalamic trauma or malignancy)
• Desmopressin (DDAVP) is a long-acting analogue of ADH (will not treat complete nephrogenic DI)
• Consider primary polydipsia (habitual drinking) as a possible alternative diagnosis

Assessment

History

• Polyuria
• urine output >4 mL/kg/hr (averaged over a 6 hour duration)
• may be higher in neonates, discuss with specialist
• Nocturia or new onset nocturnal enuresis
• Polydipsia
• drinking overnight
• persistent focus on drinking any fluid (which is unusual for child)
• drinking from unusual sources (eg animal bowls)
• Loss of weight (fluid replacing food intake and dehydration)
• Presence of intercurrent illness in a child with known DI (eg URTI, gastroenteritis)
• Past or family history of DI
• Head injury
• Constipation (from dehydration)
• Symptoms in babies can be non-specific such as irritability, poor feeding and slow growth (or excessive weight gain due to thirst managed with milk feeds)
• Neurological symptoms (eg early morning headaches, vomiting, altered sensation, weakness)
• Medications (eg diuretics)

Examination

• Dehydration
• Neurological symptoms or signs (of an underlying disease)
• Fundal examination and visual fields

Management

Investigations

• Urgent BGL (to exclude Diabetes mellitus)
• UEC, CMP
• Urine dipstick: check specific gravity, glucose
• Paired early morning urine and serum osmolality
• in DI serum osmolality is high with inappropriately dilute urine, see table below
• Consider renal ultrasound particularly if nephrogenic DI suspected

Results which may indicate particular diagnoses

• A water deprivation test will distinguish central DI from nephrogenic DI and primary polydipsia. This test should only be performed under specialist guidance, and may not be appropriate for infants <12 months due to safety
• If concern for central DI: MRI brain and pituitary, screen other anterior pituitary hormones

Treatment: Central DI

• It is vital that access to water is never limited for children with suspected or confirmed DI, as their thirst response is what keeps serum sodium in the high normal range
• Strict fluid balance chart with at least twice daily review
• Daily weight (more often may be required)
• Avoid excessive IV fluids and/or excessive desmopressin which can rapidly lead to fluid overload and life-threatening hyponatraemia

Central DI: hydration

• Perform hydration assessment
• If IV fluids are required, use sodium chloride 0.9% with glucose 5% (avoid hypotonic fluids)
• Correct electrolyte imbalances and serum osmolality slowly
• if serum sodium ≥170 mmol/L, seek specialist advice and consider ICU
• if serum sodium 150-169 mmol/L replace free water deficit slowly over 48 hours, see Hypernatraemia and seek specialist advice
• Immediately after neurosurgery, a triphasic response (immediate DI followed by a variable period of SIADH and subsequent permanent DI) may occur. During this period, fluid and electrolyte balance will require very close monitoring by neurosurgery and endocrinology. Desmopressin treatment is generally given as needed rather than regularly until risk of SIADH and sudden hyponatraemia has passed

Central DI: initiate desmopressin to reduce urine output

• All children should be discussed with endocrinology before starting or modifying desmopressin treatment
• Desmopressin effect is all or nothing, although dose required to achieve this may vary. Subsequent changes to dose will determine the duration of action (8-24 hours) rather than the degree of response
• Dosing routes include oral, intranasal, subcutaneous, intramuscular and intravenous. Care should be taken as dosing routes are not equivalent

Central DI: ongoing desmopressin use

• Discuss with specialist before discontinuing or withholding regular desmopressin in children with known central DI
• Children with known central DI may also have adrenal insufficiency. If they are unwell the need for stress dose steroids must also be considered
• Children with impaired thirst will require specialist input for fluid prescription alongside their desmopressin dosing
• When a child is unwell or modifying treatment, perform daily UEC and osmolality and paired urine osmolality until stable. More frequent UEC if correcting hypernatraemia or concerns about fluid balance
• Desmopressin administration practice points
  • Ensure serum sodium result is ≥135 mmol/L (or higher threshold as directed) within 1-2 hours prior to administration of desmopressin dose
  • Check urine specific gravity and document (dilute <1.005) prior to every dose
  • 1-2 hours of diuresis is required prior to further doses to allow free water clearance
  • If urine output >4 mL/kg/hr for 2 consecutive hours, may need repeat serum sodium and consideration of higher or repeat desmopressin dosing
  • If desmopressin due and there has been no urine output for previous 12 hours, may need to reduce or withhold the dose
  • Seek further specialist advice before administration if in any doubt

Treatment: Nephrogenic DI

• All children should be managed in conjunction with a paediatric nephrologist and dietician
• Generally older children with intact thirst will be able to regulate their own water intake
• Babies and young infants may require nasogastric/PEG fluids to maintain sufficient fluid intake
• Low solute (low-sodium, low-protein) diet to reduce urine solute load and urine output
• Consider thiazide diuretics
• Rarely desmopressin may be considered in difficult, non-genetic cases as there may be a partial response
• Correct any calcium, potassium or magnesium imbalances

Nephrogenic DI: hydration

• Beyond a 10 mL/kg bolus of sodium chloride 0.9% for emergency resuscitation, all fluid management for children with nephrogenic DI must be discussed with a nephrologist

For genetic nephrogenic DI:

• Seek nephrologist input early
• The safest option is enteral free water replacement and careful monitoring of serum sodium
• If enteral fluids are contraindicated, glucose 5% can be used
• Sodium chloride containing fluids must not be used for ongoing management without nephrology consultation due to risk of worsening hypernatraemic dehydration

Consider consultation with local paediatric team when

Any child with polydipsia or polyuria

Consider consultation with local endocrinology or nephrology team when

• All children requiring investigation for DI or starting or modifying desmopressin treatment
• All children with known central or nephrogenic DI and impaired thirst admitted to hospital or those with reduced access to free water (eg required to fast, immobilised due to a cast, sedated or intubated)
• Any child with nephrogenic DI at risk of/with hypernatraemic dehydration

Consider transfer when

• Any child with severe hypernatraemia (>170 mmol/L)
• Any child with complex fluid balance and electrolyte management
• Child requires care beyond the comfort level of local services

For emergency advice and paediatric or neonatal ICU transfers, see Retrieval Services

Consider discharge when

Family able to monitor thirst and urine output, and are aware of when to seek advice as per specialist guidance

Parent information

Hormones and me – Diabetes Insipidus

Last updated May 2022