Chronic kidney disease — new approaches to classification
By Andrea Devaney, DipClinPharm, MRPharmS, and Charlie Tomson DM, FRCP
Recent changes to the classification of chronic kidney
disease have introduced new ways of measuring renal function. This article
describes differences in the techniques used and highlights the problems
this may cause in practice
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This article as FULL TEXT PDF (130K) |
Andrea Devaney is
lead renal pharmacist at the Oxford Radcliffe Hospitals NHS Trust
and a committee member of the UK Renal Pharmacy Group, on whose
behalf this article was written.
Charlie Tomson is consultant nephrologist
at Southmead Hospital, Bristol and chaired the group that developed
the UK guidelines on chronic kidney disease. |
Kidney Research UK
In the UK 110 patients per million population start dialysis each
year |
SUMMARY
Over the past few years the terminology used to describe kidney disease
has changed. Previously, as the kidneys became less and less able to do their
normal work of cleaning the blood and producing urine from the waste products,
patients were said to have chronic renal or kidney failure. The term “end
stage renal failure” was used to describe those patients requiring dialysis
or a transplant in order to stay alive. Chronic renal failure was categorised
into mild, moderate or severe renal impairment.
However, following the UK adoption of the US Kidney Disease Quality Outcomes
Initiative (K/DOQI) in 2003, these terms have been replaced by the term “chronic
kidney disease” (CKD) with the patient’s level of renal impairment
graded from stage 1 (near normal) to stage 5 (established renal failure or
on dialysis).
End stage renal failure is now referred to as established renal failure (ERF).
ERF is relatively rare, but treatment with dialysis or transplantation is expensive,
costing over 2 per cent of the total NHS budget. In the UK, 110 patients per
million population start dialysis each year. Early CKD is more common. CKD
has a number of possible causes, but the effects are invariably the same, and
referral of all patients with early CKD would overwhelm existing specialist
renal services.
The aim of this article is to alert pharmacists and prescribers to the new
classification of CKD and the subsequent clinical biochemistry laboratory reporting
of estimated glomerular filtration rate (eGFR) and serum creatinine concentrations.
It will explain the differences between the different measurements of renal
function and highlight the problems in practice associated with these changes.
One of the biggest challenges facing all prescribers and pharmacists is adaptation
and use of the new classification system to ensure safe clinical practice,
especially with regard to accurate drug dosing for each patient’s degree
of CKD. The grouping of CKD into five stages now supersedes and conflicts with
other advice on grading of renal impairment. For example, the British National
Formulary (no.52) states that “for prescribing purposes, in the BNF,
renal impairment is arbitrarily divided into 3 grades”.
In our opinion, this advice is no longer reflective of clinical practice. The
BNF says “Renal function is measured either in terms of glomerular filtration
rate estimated from a formula derived from Modification of Diet in Renal Disease
study (‘MDRD formula’ that uses serum creatinine, age, sex and
race) or it can be expressed as creatinine clearance (best derived from a 24-hour
urine collection but often calculated from a formula or a nomogram that uses
serum creatinine, weight, sex and age). The serum creatinine concentration
is sometimes used instead as a measure of renal function, but is only a rough
guide.”
The BNF does not make any recommendation on which nomogram should be used for
correcting for age, weight and sex.
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Hospital
Pharmacist