Everyone has two kidneys, which are located in your lower back below your ribcage (although you can function with just one). They filter toxins and waste products from your blood, which are then converted into urine and expelled from your body via the bladder. Your kidneys also regulate your blood pressure and the production of red blood cells.
There are various diseases of the kidneys, collectively known as 'chronic kidney disease' (CKD), which can be caused by conditions such as high blood pressure and diabetes. This is because diabetic people may have high glucose levels which can damage the kidneys' blood vessels. High blood pressure causes similar damage.
HIV itself can cause specific kidney damage known as 'HIV associated nephropathy' (HIVAN) where the kidneys become inflamed. Links have been made between the NRTI antiretroviral drug Tenofovir (also found in the combination drugs Truvada and Atripla) and impaired kidney function. Two protease inhibitors, Atazanavir and the rarely-used Indinavir, have been linked to kidney stones - crystals which form inside the kidney and cause pain as your body tries to pass them out through your bladder.
Symptoms of a decline in kidney function can include headaches, tiredness, nausea, muscle cramps and a reduced flow of urine. Most people with HIV will be offered regular kidney function tests and if your healthcare team detects any problems you will be monitored more closely so the problem can be managed.
Tests often look for protein in the urine, as it should only be found in the blood. They also look for creatinine, a waste product, in the blood. If the levels of creatinine are high it shows that the kidneys are having trouble removing it. High blood pressure can be picked up in routine tests and may be a sign of kidney damage.
If kidney problems become more serious you might require dialysis, which is where your blood is filtered medically. It is also possible to have a kidney transplant if necessary - having HIV doesn't exclude you from this.