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Polyuria

Checked: 23-08-2021 by Vicky Ryan Next Review: 23-08-2022

Overview

These guidelines have been provided by the Endocrinology Team at NBT so pathways might be slightly different at UHBW

Definition

The production of abnormally large volumes of (usually dilute) urine. Clinically defined as >3/L of urine in 24 hours

Often occurs in conjunction with polydipsia and may be either a cause or effect

Distinguish as separate from urinary frequency. This is the excessive need to urinate which is not normal for the patient; but the total volume of urine passed is within normal limits

Important points

Determine the patient’s daily fluid intake (to determine whether this in excess) and their urine output – this can be done at home with a fluid chart

Take a full drug history to consider drugs that can cause polyuria e.g. diuretics, caffeine, alcohol, lithium (causing nephrogenic diabetes insipidus)

Clinical examination should focus on blood pressure, signs of dehydration and weight loss (e.g. diabetes, thyrotoxicosis). Clinical examination rarely reveals specific findings but may point towards the diagnosis based on the diseases most likely to cause polyuria:

Common – drugs (as above), diabetes mellitus, heart failure
Infrequent – hypercalcaemia, hyperthyroidism
Rare – chronic renal failure, primary polydipsia
Very rare – diabetes insipidus

Who to refer

Non urgent referral via eRS for the following cases:

An early morning random serum osmolality ≥295mOsmol/Kg or hypernatraemia (Na≥145 mmol/L) with no obvious cause

An early morning random urine osmolality between 200 and 750 mOsm/kg – may benefit from further investigation/clinic review

Red Flags

An urgent referral via eRS is advised if the random early morning urine osmolality is <200 mOsm/kg in a patient who has normal oral intake. These patients are likely to need a formal water deprivation test organising.

Before referral

Further investigations

Confirm polyuria based on the 24 hour urine volume i.e. >3L in 24 hours

U&Es, calcium group

TFTs – TSH, free T4

Random fasting glucose or HbA1c

Urine MC&S – exclude a UTI

Early morning random paired urine and serum osmolality and urine sodium

If there is evidence of preserved ability to concentrate the urine e.g. urine osmolality> 750 mOsm/kg, the diagnosis of diabetes insipidus is very unlikely and further investigation is not necessary
A urine osmolality of <200 mOsm/kg indicates suppressed antidiuretic hormone secretion. Assuming the patient has a normal oral intake, this is suggestive of diabetes insipidus

Services

Endocrinology NBT

Endocrinology UHBW

Resources

References:

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