The kidneys are bean shaped, each a little smaller than the size of a fist, and lie in the upper back, just below the ribcage. They filter the blood to remove waste products and control the amount of water in the body.
It is not clear why there are normally two kidneys. The human body does not need two kidneys, it could manage perfectly well with one kidney. It may just be that it has been useful for us to develop some parts of the body in pairs (arms and legs), so other parts doubled up as well. It is also possible that there is an evolutionary advantage in having a spare kidney, and this is certainly important in modern medicine, because people can live live normal lives with one normal kidney.
If one kidney is small and the other one is completely normal, it is usually possible to lead a normal life without problems. However, if both kidneys are small, there may be kidney failure. Also, the one small kidney can cause problems such as high blood pressure, even if the other kidney is normal. Therefore people who are found to have a small kidney normally have some medical tests performed to see whether further treatment or observation over a period of time is necessary.
Many people lead a completely normal life with a single kidney. There are, however, many causes of a single kidney, and the outlook depends on the cause and on the condition of the single kidney. The causes are listed below.
The commonest causes of a small kidney are:-
Tests are performed to determine whether the better kidney is completely normal, and also to determine the cause of the small or missing kidney. The exact tests needed depend upon the details of each individual case. Some of the following will be performed:-
Many people with a small or single kidney have excellent health with no problems. The chances of complications or problems developing depend on the cause and severity in each individual. The specialist should advise each individual about problems that could develop in their case. Some of the problems that can be seen are:-
Many people need no treatment.
If there are urine infections, a high daily fluid intake may reduce the frequency of infection. In women, emptying the bladder after sexual intercourse may reduce infection rates. Cranberry juice, drunk daily, has been shown to reduce urine infections in some people with recurrent infections. Urine infection is also treated with antibiotics, and in some people with recurrent infections, long courses of antibiotics may be used. Lifelong treatment is sometimes used. Long term antibiotics may encourage the development of bugs resistant to the antibiotic, but either by switching to a different class of antibiotic when an infection occurs, or by using a different preventative antibiotic on a monthly cycle, resistance problems can be reduced.
High blood pressure, if it develops, usually requires drug treatment. Losing weight and reducing salt and alcohol intake may reduce the blood pressure.
Painkillers may be needed if a kidney is painful. Paracetamol can be used safely in people with kidney diseases, but do not exceed the maximum recommended dose. Ibuprofen (on sale in the UK as ‘Nurofen’ or ‘Advil’) is an effective painkiller but may not be suitable for people with kidney trouble, and a doctor should be consulted before the use of ibuprofen. Other painkillers can be used, as recommended by each persons doctor.
Surgical removal of a small kidney is often performed, but is not always necessary. If a small kidney is causing no problems there is no need to remove it. If the kidney is causing pain or recurrent infection, or is suspected to be a cause of high blood pressure, removal may be indicated. Doctors are usually reluctant to remove a kidney that is doing useful work, even if it is causing some trouble, in case a problem develops with the better kidney in the future. If a small kidney is providing more than 25% (one quarter) of the total level of kidney function (this can be measured using a test called a radioisotope scan), doctors often suggest trying to control any problems caused by the kidney with drugs (such as long term antibiotics for infection), before removing the kidney.
If the cause of a small kidney is reflux nephropathy or congenital dysplasia (the meaning of these terms is described above), some checks in the family should be performed. Although doctors recognise that these conditions can run in families, the rules of inheritance are not precise, and there are at present no genetic blood tests or DNA tests that can be used to check for the conditions. Therefore family screening consists of checking the kidneys by ultrasound scan (a simple test in the X-ray department).
The exact recommendations vary slightly from centre to centre, and are changing quickly as the understanding of kidney diseases improves. The information given here can only be a rough guide, and anyone concerned should consult their local specialist. At present, the author suggests that if someone has a small kidney from reflux nephropathy or congenital dysplasia, that their children have an ultrasound scan to check the sizes and shapes of the kidneys. If there are any abnormalities, a specialist should be consulted. If the child of someone with reflux nephropathy has a normal scan but has repeated urine infections, a specialist should also be seen. The parents and brothers and sisters of the affected person can also be checked, if they wish, with an ultrasound scan of the kidneys. If a brother or sister has a normal scan, their children need not be checked unless they have recurrent urine infections, or there is a strong family history of kidney failure.
So long as the other kidney is normal and there are none of the complications listed above, life should be normal. It will probably be necessary to mention the problem when applying for life insurance or illness insurance, and an insurance company may ask for a specialist report. Women should usually be able to have a normal pregnancy, though problems such as urine infection or high blood pressure may appear for the first time during pregnancy. Doctors and midwives will undertake careful observation during pregnancy in someone known to have kidney problems
NKF Controlled Document No. 39, Small or Single Kidney, written 15 March 2002. Last reviewed 29 November 2012.
The National Kidney Federation cannot accept responsibility for information provided. The above is for guidance only. Patients are advised to seek further information from their own doctor.