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Re: standardised test profile - RENAL FUNCTION TESTS I have several concerns relating to the proposed order set for renal function testing. Firstly, the profile should be called ‘kidney function profile’ rather than ‘renal function profile’. Patients carry their request forms to phlebotomy appointments and should be helped to understand the tests that are being done on them. ‘Kidney’ an English word, is more intuitively understood than ‘renal’ a Latin word. The authors have interpreted their remit as being to define a ‘urea and electrolyte profile’ rather than a kidney function test profile (in fairness, it would appear that the remit actually appended this work as such). By definition, then, such a profile must include urea. My following comments relate to the definition and composition of a kidney function test profile rather than a urea and electrolyte profile, which latter consideration would be a pointless exercise. It is widely accepted that urea is an extremely poor marker of kidney function, being influenced by a range of extra-renal factors. Many laboratories, including our own, have dropped urea from their kidney function test profile. In terms of directly measured components, our own profile now consists of sodium, potassium and creatinine only, with urea still being available when specifically requested. Indeed, such practice has now been adopted across Kent with significant cost-benefit to the NHS and no apparent substantiated clinical dissatisfaction with the service. In my opinion it would be a retrograde step to suggest that a national profile should include urea. The authors provide no good rationale to support such an inclusion. They suggest that understanding the combined and sometimes counteractive influences of variations in endogenous urea production and tubular reabsorption of urea ‘can provide clinical insights into the causes of perturbations of serum …urea and thus it is appropriate that this analyte should be retained within the collective’. This makes no sense. The aim is to understand the patient’s renal function, not their serum urea concentration. Whilst it is always interesting to hypothesise on the possible causes of relative discrepancies between urea and creatinine concentrations this is not a justification for measuring both analytes on each occasion. I am extremely concerned at the suggestion that eGFR should ‘never form part of the [sic] U&E profile’. One of the justifications for this statement is that this would generate a large proportion of inappropriate estimates, particularly in the acutely ill. I presume that this refers to the setting of acute kidney injury (acute renal failure) in which it is true that eGFR may be unreliable due to the delay in equilibration between biological pools. However, it is only unreliable because the creatinine concentration from which it is derived is also an inaccurate reflection of the current state of renal function. Is it proposed that we abandon creatinine measurement in this setting? It must be noted that in nearly all of the situations in which eGFR is considered less reliable, it is so because the underlying creatinine estimation is also unreliable. In my experience, clinical users find eGFR reporting useful irrespective of whether the patient is in hospital or the community. Further, In terms of acutely ill people generally, it must be noted that serum urea concentration is an even worse marker of kidney function. The authors further allude to unnecessary angst being generated amongst older people as a result of automatic eGFR reporting. I accept that this is a controversial area, but there is no good evidence to suggest that the decline in GFR that occurs, on average, as a result of ageing, is the result of anything other than pathology. There is also no evidence to suggest that the secondary complications of kidney disease occur at a different level of GFR in older people than younger people. An analogy to this approach would be to use higher thresholds for glucose intolerance/diabetes mellitus in older people, which few would advocate. It should be noted that the Renal NSF part 2, which applies to England, stated unequivocally that “local health organisations can work with pathology services and networks to develop protocols for measuring kidney function by serum creatinine concentration together with a formula-based estimation of GFR, calculated and reported automatically by all clinical biochemistry laboratories”. Further, the Department of Health recommended the introduction of routine eGFR reporting on the 1st April 2006, to coincide with the Quality and Outcomes Framework for renal disease coming into effect. A request for a kidney function test is a request for information that will give the physician a better understanding of the patient’s renal function. It is widely accepted both nationally and internationally that eGFR, calculated using the MDRD formula, is a better indicator of kidney function than creatinine alone. It is therefore imperative that eGFR should be included within a national kidney function test profile. One would hope that a recommendation emanating from the Association for Clinical Biochemistry will not fly in the face of national recommendations. Edmund Lamb ------ACB discussion List Information-------- This is an open discussion list for the academic and clinical community working in clinical biochemistry. 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