Kidney health

How and why is kidney function monitored?

It is NHS policy that all adults over 40 who are at an increased risk of developing kidney problems should be having their kidney function checked. People with long term conditions such as diabetes or cardiovascular disease, a history of kidney problems, or a family history of severe kidney disease should already be having their kidney function checked routinely. All other adults aged over 40 should now be invited for a 5-yearly NHS Health Check and may be considered for kidney function tests as part of that.

How is kidney function measured?

Kidney performance is measured using a simple blood test in combination with a urine test. The level of a waste product in the blood called creatinine is converted into a measure of how efficiently the kidneys are filtering the blood; this is called the estimated glomerular filtration rate (eGFR). The conversion formula takes into account the patient’s age, sex, and ethnicity, as well as the creatinine itself. An eGFR of 100mls per minute is normal, so you may find it convenient to think of this as being 100% efficient, while an eGFR of 50 means the kidneys are working at 50% efficiency, in other words, half as well as they should. An eGFR above 60 accompanied by raised levels of protein in the urine represents chronic kidney disease stages 1 – 2. An eGFR of between 59 and 30 regardless of the level of protein in the urine equates to stage 3 chronic kidney disease. An eGFR below 30, or a sustained decrease in eGFR of 25% or more, should trigger the GP to consider referral to a hospital specialist.

Stages of Chronic Kidney Disease (CKD)
The eGFR is only an estimate; it varies between tests and can go up as well as down. It is possible to have an isolated low eGFR test result due to an episode of illness, a change in medications that can affect kidney function, or a technical problem at the laboratory, in which case the test will be repeated.

Graph showing an example of the eGFR declining then stabilising over time
 

How often should kidney function be monitored?

People found to have a mild to moderate decline in kidney performance (CKD stages 1 – 3) on repeated tests over a three month period should be monitored by their GP through regular blood tests to check whether the eGFR remains stable or is getting lower; a urine sample should also be taken to check for protein. The frequency of monitoring recommended by NICE varies between once a year to two or more times a year depending on: the stage of CKD and level of protein in the urine, past patterns of the eGFR and creatinine levels, the underlying cause of the CKD, other illnesses and long term conditions present, and the patient’s wishes.
Doctors disagree about whether to tell patients if they have signs that their kidneys are not working as well as they used to. Some think that patients need to be aware of this so that they can take steps to stay as healthy as possible (see ‘Why is kidney health important?’). Others are reluctant to tell patients they have early stage kidney disease or impairment because they feel it could cause unnecessary anxiety, particularly in those patients who have other health problems that are impacting on their life and whose blood pressure is already controlled and have been given healthy lifestyle advice for other reasons. (See also ‘When should doctors inform people of a mild kidney impairment?’)
The risk of progression to more advanced kidney impairment and to development of cardiovascular disease can be minimised by controlling blood pressure with tablets and by following healthy lifestyle advice such as eating a healthy diet, taking exercise, avoiding smoking and becoming overweight. Stage 4 or 5 kidney impairment is managed by a hospital specialist.
NHS health policy on monitoring of early chronic kidney disease

Guidelines on early identification and management of chronic kidney disease were first published by the National Institute for Health and Care Excellence (NICE) in 2008 with the aim of reducing the proportion of cases of advanced kidney disease that were being referred late to specialist services, resulting in unnecessary suffering and deaths. The guidelines recommended that doctors should check for early changes in kidney performance in those most at risk to ensure more timely referrals, and by 2014, when the guidelines were updated and revised, the percentage of late referrals of advanced kidney disease had reduced from 30% to 19% [NICE July 2014].

In the pages that follow, we will deal with many of these issues in greater detail, based on interviews with people whose kidney performance is being monitored due to mild or moderate impairment (CKD stages 2, 3a and 3b).

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