Introduction

Nocturia is defined as the need to urinate more than once during the night. It can affect people of all ages and sexes and is present in around 1 in 3 adults aged 30 and above.¹

It is crucial to diagnose nocturia early on and determine its underlying cause to receive appropriate treatment. If left untreated, waking too often at night affects the quality of sleep and will have a negative impact on the person’s mood and mental health, as well as their daily activities and productivity.

Nocturia is an associated symptom of many health conditions affecting different body parts such as the bladder, prostate, kidney and heart. It can also be a side effect that occurs from the use of certain medications. Thus, a thorough investigation consisting of both medical examinations and diagnostic tests is important to rule out other diagnoses.

It is important to also rule out any other conditions that may present in a similar way as nocturia, such as polyuria or an overactive bladder.

Common causes of nocturia

Urological causes

1. Benign prostatic hyperplasia (BPHBPH)

An enlarged prostate is one of the common causes of nocturianocturia. As its size increases, the prostate will press against the bladder and urethra. This pressure creates the feeling of an urgency to pass urine, even when the bladder is not full.

2. Overactive bladder

An overactive bladder is a medical condition where the bladder contracts spontaneously despite not being full. This can happen anytime during the day, and at night causes nocturia.

3. Urinary tract infections (UTIs)

UTIs are bacterial infections of the urethra, bladder or kidney. Their severity depends on which organ is affected and how far the infection has spread. They are more prevalent in women as they have shorter urethras. These are mainly of concern if occurring in males or pregnant women. Any patient in these categories suspecting the presence of having a UTI should seek immediate medical attention. Urgent help should also be sought if the patient experiences symptoms suggestive of a kidney infection, like pain in the lower part of their abdomen or in their lower back. ²

Non-urological causes

1. Diabetes Mellitus

Diabetic patients may experience an increase in thirst and would therefore consume more fluid. This increase in hydration causes the body to produce more urine, which might be excreted more often at night.

2. Congestive heart failure

In heart failure, the heart’s ability to pump blood efficiently through the body is reduced. As a result, some fluid might accumulate in the ankles and legs. When the patient lies to sleep and the feet are elevated, some of this fluid might be removed by the kidneys. This fluid is then excreted by the bladder in the form of urine, causing the person to wake more often at night.

3. Medications and excessive fluid intake

Medications such as diuretics might cause frequent urination at night. This is the case with diuretics that aid in removing fluid overload. It might be helpful to take these drugs hours before bedtime to avoid this effect.

Another contributing factor is increased consumption of fluids, mainly caffeinated ones, right before sleeping. Anyone with nocturia should aim to stop drinking a few hours before retiring to bed and limit consumption of coffee and tea to the morning.

4. Sleep disorders

Sleep disorders, like obstructive sleep apnoea, are known to cause the person to wake up more frequently throughout the night. The person may need to pass urine every time they awaken and might be confused for this nocturia.

5. Hormonal changes to antidiuretic hormone (ADH)

The antidiuretic hormone is released by the hypothalamus and increases the amount of water reabsorbed from the kidney tubules into the bloodstream. Its release is significant during the nighttime but may be affected by ageing. The reduction of fluid reabsorption means a build-up of urine in the bladder at night, and more waking to excrete it. 

Diagnostic evaluation

Patient history

When evaluating a patient presenting with nocturia, a full patient history is taken. The patient is asked to give a detailed account of their symptoms, when they initially occurred and how long they have been going on for. They will be asked to describe how frequently they have to wake up at night to use the bathroom and the amount of urine they produce when doing so. The clinician would also aim to find out if the patient experiences any pain when urinating or if their urine has a foul smell or any blood present in it.

The patient may be asked to keep a diary to record these details as well as their fluid intake, including how much, how often they drink water and any caffeinated drinks like coffee or tea.

A detailed history will also look at whether the patient presents with any pre-existing medical conditions such as diabetes or heart failure, as nocturia is a common symptom in both conditions.

As mentioned previously, certain medications such as diuretics may lead to an increase in urine output at night. The patient needs to provide a full list of medications they are currently taking and flag up any drugs that have been recently prescribed, in case they are contributing to the nocturia.

Physical examination

The doctor will also conduct a comprehensive physical examination. This includes looking for any swelling or tenderness in the bladder through abdominal palpation. A prostate exam may also be carried out to check for any enlargement that could be causing pressure on the bladder.

If the patient has heart failure or other renal or cardiovascular conditions, the clinician will check for any fluid accumulation in the form of swelling in the limbs and extremities.

Laboratory tests

Urinalysis

In addition to the previous examinations, the patient might need to undergo certain laboratory tests. A urinalysis may be requested to examine the urine and its contents. This will look at the colour, smell and pH of the urine. If the urine is dark or cloudy, it might be a sign of dehydration or an infection, respectively. The pH is a measure of acidity. Normal urine should have a pH between 5 and 8. A low pH might be a sign of diabetes or dehydration, and a high pH might indicate kidney issues or UTI.

Urinalysis also checks for the presence of glucose, blood, protein and bacteria in the urine. These might be the result of diabetes, kidney injury or a UTI.

Blood glucose levels

If diabetes is suspected in an individual who does not have a diagnosis, a blood test will be ordered to measure their fasting blood glucose levels. They may also have their HbA1C measured, which is a test that looks at the glucose attached to haemoglobin in red blood cells. This test gives an estimate of blood glucose for the past two to three months and is a better tool to diagnose diabetes than fasting blood glucose alone.

Serum electrolytes, creatinine and ADH

Measuring serum electrolytes, such as sodium and potassium, and creatinine levels helps in estimating kidney function. Any imbalance in electrolytes can be a sign of acute kidney injury or chronic renal issues.

A blood test might also be carried out to check levels of the antidiuretic hormone. An imbalance in the levels of ADH may signify diabetes or may be due to ageing.³

Specialised tests

1. Post-void residual urine measurement: This test observes the volume of urine remaining in the bladder after urinating. A high measurement indicates that the bladder is not emptying properly.
2. Urodynamic studies: This is a test that evaluates the person’s ability to efficiently store and excrete urine. 
3. Imaging studies: The clinician might want to obtain a scan of the kidneys to look for any stones, or of the prostate and bladder to check for enlargement and efficiency in eliminating urine, respectively.

Differential diagnosis

Polyuria vs. nocturia

When a patient presents with symptoms of increased urinary frequency, it is essential to rule out whether this is polyuria or nocturia only. Polyuria is when an increase in frequency is experienced throughout the entire day and not exclusively during the night.

The presence of nocturia alone may indicate issues with bladder storage capacity, as the bladder cannot hold the urine for an extended period of time through the night. It could also mean that the nocturia may be the result of a non-urological disorder.

Overactive bladder vs. nocturnal urinary frequency

Patients with an overactive bladder experience frequent urges to urinate both day and night. They may also have incontinence, where they involuntarily pass urine and are unable to control it. These symptoms are due to involuntary contractions of the bladder occurring when it is not even full of urine, creating a false feeling of urgency to urinate.

As with polyuria, nocturia is not present in isolation but is rather a manifestation of the overactive bladder.

Nocturnal polyuria vs. sleep apnoea

In many cases, the patients might have an underlying sleep disorder, such as obstructive sleep apnoea, causing them to wake constantly at night. It is estimated that nocturia is experienced by 50% of patients suffering from sleep apnoea.⁴

Patients sometimes mistake nocturia as the reason for their frequent waking at night when it is in fact the result of their sleep disorder.

A diagnosis of sleep disorders should be considered if the patient reports difficulty returning to sleep or feeling exhausted in the morning.

Other diagnoses

As previously stated, nocturia could be a sign of other non-urological conditions. If this is the case, tests should be conducted to confirm the suspected diagnosis.

This is often the case when the patient presents with symptoms or test results pointing towards diabetes, heart failure or kidney injury.

If any prostate involvement is observed, the clinician will need to determine whether the enlargement is benign or caused by tumours in the case of prostate cancer.

Summary

• Nocturia, which is waking up more than once at night to urinate, is a common symptom of many medical conditions. Unlike polyuria, it only occurs during nighttime and not throughout the day
• It may signal an underlying condition such as diabetes or congenital heart failure, which can be confirmed by running extra tests
• It should also be considered when assessing kidney function, and any suspected renal  deterioration can be determined by measuring serum electrolytes and creatinine
• Other causes include sleep disorders like obstructive sleep apnoea, or the presence of an enlarged prostate or prostate cancer in men
• A thorough medical examination and proper testing are of utmost importance in determining the exact cause of nocturnal polyuria. This would help in ensuring the patient receives the correct treatment and their quality of sleep is improved