Renal function is the key indicator of the kidneys’ condition and should be monitored in all deteriorating or
critically ill patients in order to:
Monitor disease progress
Assess baseline measurements before starting treatment with certain medicines
Indicate the function of other systems (e.g., cardiovascular system, where low cardiac output will result in
diminished urine output)
Identify renal impairment.
This article will discuss the principles of monitoring renal failure.
The kidneys, located near the middle of the back, just below the rib cage, have several functions, which include:
Secretion of hormones such as:
Renin: Is vital for the activation of the renin-angiotensin-aldosterone system, which plays a vital role
in increasing blood volume regulation of fluid balance
Erythropoietin, which is synthesized in the kidney and stimulates the bone marrow to produce red blood
Regulation and maintenance of:
Excretion of foreign materials such as medicines and by-products of metabolism, nitrogen, urea, and
Maintenance of calcium and phosphorus balance, and activation of vitamin D.
(You and Your Hormones 2019; NIDDK 2018; Gounden et al. 2023)
Principles of Urinalysis
A urinalysis can provide healthcare professionals with valuable information about the patient’s health status. For
example, urinalysis can provide indications of kidney disease, diabetes mellitus, liver disease, urinary tract
infection (UTI), and general dehydration (Milani & Jialal 2023).
The Purpose of Urinalysis
Screening for systematic diseases such as renal conditions and diabetes mellitus
Diagnosis - to confirm and exclude suspected conditions, for example, UTIs
Management and planning - to monitor the progress of an existing condition and plan programs of care.
(Milani & Jialal 2023)
Appearance of Urine
The colour of urine can vary greatly. Normal urine varies in appearance from clear to straw-coloured and is practically odourless but becomes turbid and smells of ammonia if left to stand (Rotker & Watson 2023; Labpedia.net 2023).
Variations in the appearance of urine include the following:
Clear: Very clear and colourless urine may indicate excessive fluid intake. It may also be caused by
pharmacologically induced diuresis or diabetes insipidus/diabetes mellitus
Dark: Urine is concentrated as seen in fluid depletion or contains conjugated bilirubin and jaundice
Orange: Can indicate dehydration, or can be caused by certain vitamins or medications
Pink/red: May indicate haematuria, though other causes include ingestion of certain foodstuffs like beetroot
Cloudy: May indicate the presence of pus, protein or white blood cells and requires further investigation
Sediment: Can indicate a range of conditions, such as urinary tract infection, diabetes and bladder stones
Frothy: May indicate significant proteinuria.
(Chavoustie & Sissons 2023; Cadogan 2023; Haase 2022; Luo & Herndon 2023; Mayo Clinic 2023)
Normal, freshly voided urine is practically odourless. If left to stand for several hours, it acquires a mild smell of ammonia
Infected urine has a ‘fishy’ smell
In patients with diabetes who have ketoacidosis, acetone is excreted in the urine, causing the urine to smell uncharacteristically sweet. Acetone can also indicate starvation.
(Labpedia.net 2023; Biggers & Gotter 2018; ACT Health 2019)
A dipstick urinalysis can accurately show the presence of a variety of substances such as protein, glucose, blood, and ketones as well as the PH.
To ensure reliable results:
Always use a fresh sample of urine collected in a clean receptacle
Observe the sample for colour, appearance, smell and debris
Ensure that the reagent strip is in date
Ensure that the whole of the reagent strip is immersed in the urine sample
Tap the strip on the side to remove excess urine, place horizontal and compare reagent pads with the colour scale at time intervals stipulated by the manufacturer, documenting results immediately
Safely discard the strip and urine sample
Store reagent strips following the manufacturer’s recommendations.
(ACT Health 2019; Jevon 2012)
Significance of Urinalysis Results
Glucose in urine indicates that blood glucose is raised and the consolidation of glucose in the plasma exceeds the renal threshold. Causes include diabetes mellitus, Cushing’s syndrome and stress
Ketones are by-products of fat metabolism and are suggestive of excessive fat breakdown as in starvation, fasting and uncontrolled diabetes
Proteinuria is the presence of abnormally large quantities of protein. Persistent proteinuria is typically a sign of renal disease
Haematuria (presence of blood) is associated with diseases of the kidney or urinary tract; it can also be present during menstruation
Nitrate is strongly indicative of infection, although negative results can’t rule out infection
White blood cells (pyuria) usually indicate an infection somewhere along the urinary tract and are an indication for laboratory testing.
(ACT Health 2019; National Kidney Foundation 2022; Cleveland Clinic 2022)
Principles of Urine Output Monitoring
Urine output is frequently used as a guide to the adequacy of cardiac output (renal perfusion amounts to 20 to 25% of the cardiac output)
The average urine output in a healthy adult is 800 to 2,000 mL/day
All critically ill patients will require a urinary catheter to measure urine output and generally, an hourly urine drainage bag will be attached
The urinary catheter should be closely monitored for blockages or occlusions
If urine output dramatically falls, always consider mechanical obstruction first
Sometimes bladder washouts are indicated (intermittent or continuous).
(Kaufman et al. 2023; MedlinePlus 2023; ACI 2022)
Principles of Monitoring Fluid Balance
Monitoring fluid balance in critical illness is essential. Having an understanding of disease processes is essential because clinical conditions can deteriorate rapidly.
Careful monitoring of the fluid balance chart (input and output) must be maintained
The patient should also be monitored for signs of fluid loss/gain
Daily measurement of serum sodium, potassium, urea and creatinine is required to assess fluid and electrolyte
Fluid balance charts from the preceding few days should be compared with serum and urine urea and electrolyte
values to help evaluate the patient’s response to fluid administration and guide the fluid regimen over the
next 12 to 24 hours.
(Murphy and Byrne 2010)
Acute Renal Failure
Acute renal failure (ARF) is characterized by a rapid decrease in the kidneys’ ability to eliminate waste products, which results in an accumulation of urea and creatinine (Malkina 2023).
ARF can be classified according to precipitating factors. For example:
Prerenal: Caused by inadequate renal perfusion due to:
A decreased intravascular volume such as dehydration, haemorrhage or hypovoleamic shock
Cardiovascular failure such as heart failure, myocardial infarction (MI) or cardiogenic shock
Medicines such as angiotensin-converting enzyme (ACE) inhibitors, non-steroidal anti-inflammatory
drugs (NSAIDs) or anaesthetics
Decreased effective renal perfusion due to sepsis, cirrhosis or neurogenic shock
Intrinsic: Occurs when there is structural damage to the renal parenchyma such as acute tubular necrosis
(ATN). ATN occurs because of sustained renal hypoperfusion.
Postrenal: Caused by obstruction of urine drainage due to ureteral obstruction such as stones, blood clots or
(Goyal et al. 2023)
Monitoring renal function is essential to the care of a deteriorating or critically ill patient. It can provide
indications of kidney function as well as the performance of other major body systems.
Lydia Nabwami is registered nurse who has worked in various healthcare settings including cardiac ward, cardiac critical care unit (ITU), general ITU, A&E department, nursing homes and community nursing. She uses her experience as a RN to write well-researched content that helps to attract and motivate audiences. Lydia is also a freelance writer for hire with specialisation in health writing and has helped numerous companies with their content needs. Her work has appeared on sites such as Caring Village, Reachout, Lisa Nelson RD and more. When she isn’t writing, you can find her listening to motivational speeches, keeping active or playing with her two daughters. Contact Lydia or visit her website at Lnwritingservices.co.uk for more information on her services.