What is CKD?

What is CKD (chronic kidney disease)?

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Chronic kidney disease (CKD) is a long-term condition where the kidneys do not work as well as they should, or are damaged in some way. It is not always serious.

It affects 10% of the population, but only 1% of them will need dialysis or a kidney transplant – i.e. 1 in 1000 of the population.

Urinary tract

The kidneys are part of the urinary tract. This is a group of organs that act as the body’s dustmen, and get rid of waste products from food and extra water in the blood for you, 24 hours a day.

The disease is called ‘chronic’ because the damage to your kidneys happens slowly over a long period of time – usually over months or years.

This damage can cause wastes to build up in your blood and body; or some other evidence damage to the kidneys (e.g, protein in urine).

CKD can also cause other health problems, especially related to the heart and blood pressure. In most people it is a ‘silent disease’, i.e. they do not know they have it – like high blood pressure, high cholesterol and early diabetes.

So. What is chronic kidney disease (CKD)?

Let’s start with a definition.

How is CKD defined?

Simple definition 1 (simple): a long-term condition where the kidneys do not work as well as they should, or are damaged in some way.

Precise definition 2 (more complex and accurate, used by doctors): with 2 types ..

1. ‘Functional CKD’ = an estimated glomerular filtration rate (eGFR; see below) of <60 mL/min – that is present for at least three months (i.e. measured at least twice), with or without evidence of kidney damage; or,
2. ‘Structural CKD’ = evidence of kidney damage with or without decreased GFR – that is present for at least three months, as shown (by 1 or more of):

• • Albuminuria (protein in urine),
  • Haematuria (blood in urine, after exclusion of urological causes),
  • Structural abnormalities (e.g. polycystic kidneys) on renal ultrasound)
  • Pathological abnormalities (e.g. on kidney biopsy)
  • Electrolyte and other abnormalities due to tubular disorders
  • History of kidney transplantation.

This definition is based on the 2024 KDIGO CKD guideline (Stevens, 2024).

Note. In other words, in some cases of CKD there is evidence of kidney damage but normal renal function (normal GFR and creatinine).

5 Stage Classification of CKD

5 Stages of CKD

The diagnosis of CKD is largely based on a classification of its severity, based on GFR (glomerular filtration rate) – the higher the eGFR, the better.

Normal GFR in humans is 90-120 mls/min.

The GFR is calculated from the blood creatinine level (normal range 60-120 mcmol/L) –  i.e. the lower the creatinine, the higher is the GFR, the better.

What do these 5 stages of CKD mean?

• CKD1+2 – risk factors for CKD (eGFR 60-120 ml/min)
• CKD3A – mild CKD (eGFR 45-59 ml/min)
• CKD3B – mild-moderate CKD (eGFR 30-44 ml/min)
• CKD4 – moderate CKD (eGFR 15-29 ml/min)
• CKD5 – severe CKD (kidney failure) (eGFR < 15 ml/min)

But what do these stages really mean?

• CKD1-2 means you can have an abnormal kidney structure with normal kidney function
• CKD3 means you may have a mild or moderate problem with kidney function
• CKD4 means you do have significantly reduced kidney function, and may require dialysis or a kidney transplant one day
• CKD5 means you will require dialysis, or a kidney transplant, or supportive care (no dialysis).

How common is CKD?

As we have said, about 1 in 10 people have CKD, i.e. its very common. Fortunately in most people, it is mild and more of a risk factor than disease.

However, in 1 in 100 people with CKD, kidney function gets worse over time, and develop kidney failure (stage 5 CKD).

This equates to 1 in 1000 of the population. They will then need dialysis or a kidney transplant.

Age is the primary risk factor for CKD:

• CKD is present in 25% of people aged 65-74 years, and 50% in people over 75 years. In many of these it is really part of the ageing process and not a disease
• It is less common in young adults, being present in 1 in 50 people
• The average age range of starting dialysis is 60-65 years old.

Approximately 70,000 people in the UK are on dialysis or have a transplant. This means that each GP will have two such patients ‘on their books’. This is why they cannot be expected to be experts in the condition.

Summary

We have described what is chronic kidney disease (CKD). Chronic kidney disease is an important focus of this website. So, hopefully by reading our articles you will get a better understanding of what is chronic kidney disease.

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