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Kendrick asks....what’s the point of measuring eGFR?

Our clinical columnist Dr Malcolm Kendrick questions why everyone with an eGFR of less than 60 should be told they're ill

Our clinical columnist Dr Malcolm Kendrick questions why everyone with an eGFR of less than 60 should be told they're ill

There are few things in the world of medical research that are absolutely certain. But one thing that can be stated with confidence is that, as you get older, your life expectancy decreases. Indeed, for every five years you live, you have reduced your life expectancy by five years.

Another thing that is certain is that, as you get older, your kidneys do not work as well as they did when you were younger, and your eGFR will steadily fall. By the time people reach 75, more than 50% of men and considerably more women will have an eGFR low enough to place them in category 3 to 5 of chronic kidney disease.

To quote from a recent UK study, looking at rates of CKD across the population: ‘More than half of the older people had an eGFR <60 (stage 3 to 5 CKD) and prevalence was substantially higher in the females.'1

A serious illness?

When more than 50% of a population has a ‘condition' it is difficult to see this as a serious illness. Yet, according to the UK guidelines on CKD, a GFR of below 60 is not viewed as something to be almost expected in the elderly, but as serious and significant, and a possible indicator of acute renal failure2.

It states: ‘Because acute renal failure requires emergency treatment, all patients with newly detected abnormal kidney function should be assumed to have ARF until proven otherwise, although the majority will turn out to have CKD.'

Recommended actions are:

• review of medication, particularly

recent additions such as diuretics, NSAIDs and any drug capable of causing interstitial nephritis

• clinical examination for bladder enlargement

• urinalysis: haematuria and proteinuria suggest possible glomerulonephritis, which may be rapidly progressive

• clinical assessment, looking for underlying conditions such as sepsis, heart failure, hypovolaemia

• repeat measurement of serum creatinine concentration over a maximum of five days.

In reality the issue of CKD and the CKD QOF indicators seems to be an attempt to bring two different problems under one umbrella. It is true that a low eGFR is an important indicator of potentially serious kidney disease in a younger population.

In this group, it can indicate renal artery stenosis, glomerulonephritis, polycystic kidney disease and suchlike.

Here we have a clear need for specialist management to try to prevent rapid progression to renal failure, dialysis and kidney transplantation. In such cases we are dealing with a true ‘renal' population.

But in the elderly, the eGFR is primarily an indicator of increased cardiovascular risk. We already have a whole raft of indicators for increased CVD risk. Does measuring CKD add anything significant1?

Thresholds

To quote again from last year's UK study: ‘Despite strong evidence of the causal link of diabetes and hypertension with CKD and the growing evidence that obesity and smoking are important risk factors for CKD, we found few associations with these, probably due to reverse causality and/or survivor effects. It is not clear what additional interventions to reduce cardiovascular risk would be added from knowledge of an eGFR <60.'

It seems clear that, in the elderly population, the eGFR level at which serious CKD is diagnosed is far too high. We are picking up literally millions of people with a ‘condition' that we can do nothing very much for. It is not helping us stratify CVD risk and is making very little difference to our management.

Currently, an eGFR of less than 60 has a sensitivity of 100% – it picks up everyone who may have a problem. But it has a specificity, in the elderly, of about 5%.

Many people who are, effectively, healthy for their age are being told they have CKD when they don't.

We should support those who want to lower the level at which CKD is diagnosed to less than 45. Only then will we have a reasonable screening test.

Dr Malcolm Kendrick is a GP in south Manchester

Over half of older people will have an eGFR that classes them as having CKD Over half of older people will have an eGFR that classes them as having CKD

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