Clinical management of chronic kidney disease by ProQuest


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									CME Renal medicine                                                                               Clinical Medicine 2009, Vol 9, No 3: 269–72

Clinical management                                    tified on imaging performed for other
                                                                                                      to adjust for dilution of the urine. Spot
                                                                                                      urine samples for total protein-creati-
                                                                                                      nine ratio (TPCR) or albumin-creati-
of chronic kidney                                                                                     nine ratio (ACR) perform at least as
                                                       Estimated glomerular filtration rate
                                                                                                      well as 24-hour urine samples in most
disease                                                Although serum creatinine (SCr) is a good      circumstances and are far more conve-
                                                       marker of change in GFR in an individual       nient.7 The first morning void is pre-
Shona Methven, Specialty Registrar and                 patient, it is a poor measure of absolute      ferred but random samples are
Clinical Teaching Fellow; Mark S MacGregor,            GFR.6 One major flaw is that in addition       satisfactory.
Consultant Nephrologist                                to correlating inversely with GFR, SCr also       ACR has a proven role in diabetic
The John Stevenson Lynch Renal Unit, NHS               correlates with muscle mass. eGFR is a cal-    kidney disease and should be used to
Ayrshire & Arran, Crosshouse Hospital,                 culated value derived from SCr, age,           screen for and monitor this disease.
Kilmarnock                                             gender and race6 in which these three          Whether TPCR or ACR should be used
                                                       parameters essentially provide a correction    in non-diabetic kidney disease is con-
Chronic kidney disease (CKD) is a major                for muscle mass (commonly used equa-           troversial, with guidelines making dif-
public health problem which commonly                   tions are given in Table 2). If muscle mass    fering recommendations.4,5 Most
presents to primary and secondary care.                differs substantially from the average for     research on outcomes and interven-
Reporting of estimated glomerular filtra-              age, race and gender, the eGFR will be less    tions7,8 is based on total proteinuria
tion rate (eGFR) has markedly increased                accurate. Common examples include              rather than albuminuria so the theoret-
identification of these patients. Prevalence           amputees and the malnourished. In such         ical advantages of the more costly ACR
may be genuinely rising, perhaps as a con-             patients, a 24-hour urinary creatinine         remain unproven.
sequence of diabetes mellitus and obesity.1            clearance may still be of value. eGFR has
CKD is primarily a marker of cardiovas-                been validated in whites and black
cular risk: stage 3 CKD carries a 40–100%              Americans but its reliability is unproven in
increased risk of cardiovascular events.2              other races. eGFR should not be used in        Non-visible haematuria may be detected
For the minority at risk of progressive                children, in pregnancy, the very elderly       on dipstick urinalysis. If persistent, and
decline in kidney function, prompt identi-             and those at both extremes of weight. It is    after urological causes have been excluded,
fication is necessary to allow early inter-            unreliable in liver failure.                   it should be considered a marker of kidney
vention and prevent complications.                        eGFR is increasingly inaccurate above       damage.9 It does not require confirmation
                                                       60 ml/min/1.73 m2 and many laboratories        with microscopy but warrants ongoing
Classification                                         do not report eGFR above that level.           monitoring.
                                                       Higher changes in kidney function should
The CKD classification system originated               be monitored using SCr, with a change of
in the USA and was quickly adopted inter-              more than 10–15% likely to be significant.
nationally.3 The modified version used by              SCr is increased by the ingestion of cooked    Having identified CKD on the basis of
UK guidelines is shown in Table 1.4,5 It is            meat, so confirmatory samples are best         an eGFR, a urine abnormality or
based on the GFR and the presence or                   taken after abstaining from meat for           imaging, an attempt should be made to
absence of kidney damage. The latter is                12 hours. Like SCr, eGFR reflects GFR only     establish the underlying diagnosis and
loosely defined as the persistent presence             in steady state, so both are unreliable when   prognosis. Accurate diagnosis may lead
of proteinuria (including microalbumin-                kidney function is changing rapidly (eg in     to specific therapies, in addition to gen-
uria), haematuria or structural disease of             acute kidney injury (AKI)). Having newly       eral management (discussed below).
the kidney (whether defined with imaging               identified a reduced eGFR, it is important     Conversely, extensive investigation of
or histology). The reduced GFR and/or                  to exclude AKI with a further sample           asymptomatic patients with stable CKD
damage must be present for more than                   within 1–2 weeks. To establish the diag-       stage 3, no proteinuria and no haema-
90 days to establish chronicity. (Note that            nosis of CKD requires a further sample at      turia is unlikely to be rewarding. Most
stages 1 and 2 require the presence of                 least 90 days later.                           of these patients will have simple
kidney damage whereas a reduced GFR                                                                   glomerulosclerosis. More attention is
alone is sufficient for stages 3–5.)                                                                  warranted, however, if vascular disease
                                                                                                      or risk factors are absent.
Identification and staging                             Di
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