Essentially, the Urea and Electrolytes blood test gives an overall impression of renal function – how well your kidneys are working. At London Doctors Clinic, we perform this blood test on a daily basis, as part of essential blood test investigations for our patients.

The kidneys are very important organs, although their purpose is not so well known. We all know the body's biological basics: the brain thinks; the heart pumps blood; the intestines digest food; but the kidneys...? Perhaps the kidneys are even more of an undervalued organ, since we're usually born with not one, but two of them - hence the possibility of live kidney donation from a healthy donor to a patient in kidney-failure.


So what are the kidneys, and what do they do?

The kidneys are two small kidney-bean-shaped organs, at the back of the upper abdominal area, under the rib-cage. They have a few vital functions, such as being responsible for filtering waste products from the blood stream. These waste products include electrolytes (salts and minerals) such as sodium (Na+) and potassium (K+), and also the by-products of metabolic reactions, including creatinine and urea. These electrolytes and by-products are then filtered out of the bloodstream by the kidneys, via a process called glomerular filtration.


The kidneys filter electrolytes and waste-products from the blood, excreting them in the urine.

Creatinine is an important by-product of muscle metabolism - the process to supply muscles with the energy for movement. Creatinine acts as a long-term marker of kidney disease, although levels can also be increased due to high levels of meat consumption.  Another important metabolism by-product is urea: synthesised by the liver to aid in the excretion of waste nitrogen. Urea also plays an important role in the kidneys’ exchange system, allowing water and important ions to be reabsorbed as required from the excreted urine. This control of urine output also ensures the kidneys are also responsible for the body’s fluid balance. This includes maintaining blood plasma volume, and blood pressure.

The kidneys are also important in producing an important product involved in bone health (activated vitamin D), and produce the protein erythropoietin (EPO), which is essential in the production of red blood cells.

Electrolyte levels must also be tightly controlled by the kidneys' homeostatic mechanisms: fluctuating ion levels can be dangerous. For example, hyperkalaemia (raised potassium) leads to an increase risk of potentially fatal cardiac arrest.

Overall, the kidneys are very important in homoeostasis – the maintenance of an equilibrium of important elements in the body.



Kidney Function Test

Measuring levels of such filtered electrolytes or by-products in the blood, such as urea and creatinine, can give an accurate indication of the glomerular filtration rate (GFR) – the levels at which the kidneys are functioning. So essentially, high levels of creatinine for example in the blood would be flagged up in a renal function blood test, to indicate a slow glomerular filtration rate (GFR), suggesting some sort of kidney disease or dysfunction, and the requirement of further medical investigation.

A standard kidney function blood test for urea and electrolytes would measure a variety of kidney-relevant parameters:

  • Sodium (Na+)
  • Potassium (K+)
  • Chloride (Cl-)
  • Bicarbonate (HCO3-)
  • Urea
  • Creatinine

Average recommended ranges for each parameter of the Urea and Electrolytes test. Individual recommended ranges for each may depend on patient factors such as age and gender.undefined

A GP may suggest a kidney function test for any patients with the following:

  • High blood pressure
  • Headaches
  • Recurrent urinary tract infections (UTI's)
  • Proteinuria (protein in the urine)
    • Detectable by urinalysis by urine dipstick, available for free during any GP consultation.
  • High risk of kidney disease, including a family history of the disease.


Kidney diseases

The overall purpose of this urea and electrolytes blood test is to investigate any potential renal dysfunction or disease, but can also give indications of conditions such as liver failure, Addison's disease, Cushing's disease, and the effect of medications (such as aspirinparacetamol) on renal function. 

One significant kidney disease to be aware of is Chronic Kidney Disease (CKD). This is a long-term condition, whereby the kidneys do not function as effectively as they should. Older people are more likely to be affected, with an estimated 20-25% of people over the age of 65 suffering from kidney disease to some extent.

Those who suffer from high blood pressure or diabetes are more at-risk, and should consider an annual kidney disease screen. There is no cure to this disease, although the disease can usually be managed by medication and lifestyle changes, in order to prevent further deterioration of kidney function.

Symptoms can be subtle, and may not present until after significant disease progression. These symptoms include:

  • Tiredness
  • Swollen ankles or hands (due to oedema/ water retention)
  • Shortness of breath
  • Nausea
  • Haematuria (blood in the urine). 

Severely chronic kidney disease can then lead to established kidney failure (EKF) - the loss of kidney function to a life-threatening extent. This condition is very serious, and requires dialysis or a kidney transplant, to replace the lost homeostasis and filtering functions of the kidneys.


So if you're suffering from any of the above-mentioned symptoms, or are at all concerned about your kidney function, do not hesitate in booking in a 15-minute GP consultation at LDC for just from £89. With the Urea and Electrolytes test costing just £64, and a full break-down of results in usually just a few hours, there's really no excuse not to undergo that potentially life-saving kidney check-up.