CKD fad is a triumph of fashion over sense
From Dr Dan Rutherford
St Andrews, Fife
The entire issue of chronic kidney disease is full of thinking so woolly you could knit jumpers with it – and Dr Matt Doyle's article (Registrar,
1 February) failed to tackle the two common myths about eGFR.
• Myth 1: 'eGFR is derived from a test of kidney function that we haven't previously been using.' Wrong. The only biochemical measurement of kidney function used in calculating eGFR is the serum creatinine level. That figure is then put into the context of the patient's age and sex. That's it. Unless your lab request forms are unusual you will not be entering your patient's weight or their ethnicity. Those two important factors are ignored by the eGFR formula in widespread use.
• Myth 2: 'eGFR tells you something you didn't already know.' Wrong. The vast majority of people in this country who are in the process of developing significant kidney impairment are diabetic, hypertensive or both.
If there is a part of the country in which elderly men with anuria, beach-ball sized bladders and huge prostates are going about in large numbers without being spotted by the medical profession then I'm glad I don't live there.
Similarly there must be very few adults with polycystic disease or glomerulonephritis who come to light only because their low eGFR picks them out from medical obscurity.
We already know that hypertension and diabetes are diseases in which attention to cardiovascular risk factors is extremely important, so does a low eGFR really tell us anything new in these patients, or direct us to treat them differently?
The answer would only be yes if you don't take current targets for good management of either condition seriously enough, or you still live in that era of medicine in which end stage damage is the only evidence you accept for more aggressive treatment.
Leaving aside the fact that the eGFR arithmetic was derived from people who already had renal impairment and its applicability to screening the general UK population is unproven, the introduction of CKD as a separate concept has muddied the water in diabetes and hypertension management for no discernible benefit.
It has increased lab costs by millions of pounds, generated unnecessary work for practices and got a whole section of people worried about their kidneys who will never need the attention of a nephrologist.
Of course chronic kidney disease needs to be picked up and dealt with properly, but eGFR does nothing that could not have been achieved by lab results forms quoting ranges of normal for serum creatinine that take account of the difference between men and women and the effect of ageing. The principles of treatment of CKD are the same as those of the disorder that is likely to be causing it in the first place.
Calling CKD a 'new priority for primary care' (BJGP, December 2006) is a classic example of vogueism triumphing over common sense.