A cyst is a pouch (or ‘sac’) of cells that contains fluid. It can be as small as a pea to the size of a grapefruit. ‘Polycystic’ means ‘many cysts’, which is where polycystic kidney disease gets its name.

In people with ADPKD, many cysts grow in the kidneys and increase in size over time (usually over many years). This causes the kidneys to get larger and often stops them working properly. If you have ADPKD, you’re very likely to get cysts in other organs too, such as your liver.

To filter our blood, each kidney contains up to a million filtering units known as nephrons. Each nephron is made of a filter and tiny tube (more technically known as a tubule) and blood vessels. The nephrons filter blood; the water and waste (urine) flow to the bladder.

In people with ADPKD, cysts grow from the kidney tubules.

Kidney cysts begin to form when the cells lining the tubule grow too fast, making a bulge. Over time, this balloons in size and can separate from the tubule, forming a cyst. Fluid collects in the cysts causing them to swell. This is shown in the picture below.

Some of the changes to tubule cells that lead to cysts growing are caused by an inherited altered gene (for example, PKD1 or PKD2). As the kidneys get damaged, more changes occur that can worsen cyst growth. For example, the amounts of certain molecules that control how tubule cells behave can change. The gluey substance holding tubule cells together can also weaken.

In people with ADPKD, more and more cysts form and enlarge over time. Scar tissue forms around the cysts (known as fibrosis) squashing nearby blood vessels and nephrons. Immune cells (which usually defend the body against infections) can also collect in the damaged tissue, making things worse.

These changes mean that both kidneys enlarge as a person ages. The speed at which the kidneys grow differs between people, but they tend to increase in size by about 5% each year. For example, a kidney 15 cm long could increase to almost 16 cm long in a year.

The kidneys usually continue to work well for many years despite these cysts. However, the damage to the kidneys eventually becomes too great and they stop working properly. The amount of blood they can filter per minute (the estimated glomerular filtration rate, or eGFR) drops. This is known as reduced kidney function or chronic kidney disease (CKD) stage 2, 3, 4 or 5.

On average, people with ADPKD get kidney failure at about age 60, but this differs a lot from person to person. Some people with ADPKD get kidney failure earlier, while others never get kidney failure. The timing depends on a few factors, including the gene alteration a person has (for example, PKD1 or PKD2).

Most people with ADPKD develop cysts in their liver by middle age. These cysts don’t usually cause any symptoms or stop the liver working. In some people, they increase the size of the liver but they usually don’t cause serious problems. You can learn more about liver cysts on our web page on polycystic liver disease.

Less commonly, cysts can form in other organs including:

• the pancreas (an organ that makes enzymes and hormones that aid digestion)
• the seminal vesicles (glands that release semen in men)
• the ovaries (where a woman’s eggs are made)

There’s no cure for ADPKD and no treatments can prevent the growth of cysts. However, there are some steps you can take to help slow cyst growth. We explain these below.

Diet and lifestyle

Factors that might increase the speed that ADPKD worsens include:

• being overweight or obese
• eating more salt than recommended (over 5g a day for adults)
• having high blood pressure
• being dehydrated often

So, it’s a good idea to follow a healthy diet and lifestyle. You should also take any blood pressure medicines your doctor recommends if you have high blood pressure.

Experts recommend that adults with ADPKD drink at least 2–3 litres of water a day, provided their eGFR is at least 30 ml/min per 1.72 m². If your eGFR is lower than 30 ml/min per 1.72 m² (meaning you have CKD stage 4 or 5), please follow your kidney specialist’s advice about water. If you aren’t sure what your eGFR is, ask your doctor.

Experts aren’t sure that drinking plenty of water can slow the growth of cysts. However, they think it might help and it’s unlikely to cause you harm.

Tolvaptan

A treatment called tolvaptan (Jinarc®) can slow the speed at which the kidneys enlarge and are damaged.

Researchers think tolvaptan does this by:

• stopping the growth of cells that line cysts
• reducing the amount of fluid that collects in cysts

Tolvaptan is not available to all patients. To find out more about how it works and who may be suitable, see our webpage Medicines to treat ADPKD.

• ADPKD basics
• Polycystic liver disease
• Progression of ADPKD
• Medicines to treat ADPKD

Kidney Research UK has information on what the kidneys do.

TedEd has a video on how your kidneys work.