SA JOURNAL OF DIABETES & VASCULAR DISEASE
REVIEW
VOLUME 7 NUMBER 1 • MARCH 2010
13
Diagnosing and monitoring CKD in practice
Robert Lewis
D
iagnosing chronic kidney disease (CKD) and
monitoring kidney function are key steps in
improving management. This article reviews
the recommendations on making a diagnosis of CKD,
including staging patients, and the tests available for
monitoring kidney function, with explanations of how
to test patients, what the findings mean, and how to
act on the findings.
There are two reasons why chronic kidney disease (CKD)
is relevant to primary care. Firstly, CKD indicates systemic
vascular disease and its presence is an independent marker
of cardiovascular (CV) risk.
1
Management in this first context
aims to reduce the chance of future CV events. Secondly,
some patients with CKD progress to end-stage renal disease.
Management in this second context consists of slowing
progression in the hope of averting the need for dialysis.
These two issues are related, but it is important to separate
them when evaluating the evidence supporting various
interventions.
Tests used to diagnose CKD
The diagnosis of CKD depends on two separate findings:
reduced renal excretory function
•
the presence of abnormalities (notably protein) in the
•
urine.
Renal excretory function equates to glomerular filtration
rate (GFR), which is normally in the region of 100 ml/min.
Measuring the GFR therefore gives an approximation of
percentage kidney function compared to normal. In the
absence of a simple test for GFR, various surrogates have
been used, such as blood urea, serum creatinine and, most
recently, estimated GFR (eGFR). The latter uses an empirically
derived formula which aims to improve the correlation of
serum creatinine with true GFR by correcting for age, gender
and race (with a supplemental correction factor).
2
Protein leakage into the urine signifies glomerular disease.
It may be detected by a variety of means (see Table 1), each
with advantages and disadvantages.
Albumin: creatinine ratio (ACR) is now established as the
screening method of choice for early diabetic renal disease.
In people without diabetes, proteinuria has previously
been detected with a dipstick and quantified using either
protein:creatinine ratio (PCR) or ACR. PCR has the advantage
of being less expensive than ACR and having a convenient
relationship with the (now obsolete) 24-hour urine collection
for protein excretion with which clinicians are familiar (protein
excretion in g/24 hr
=
PCR divided by 100). However, the
National Institute for Health and Clinical Excellence (NICE)
has recommended that ACR be used as the method of choice
for screening for proteinuria in all subjects (not only for those
with diabetes).
3
NICE has defined the abnormalities which constitute CKD
as:
eGFR
•
<
60 ml/min on three consecutive occasions within
a period of no less than 90 days.
In people without diabetes, ACR
•
>
30 mg/mmol or
PCR
>
50 mg/mmol. NB: people with diabetes have
microalbuminuria when ACR
>
2.5 mg/mmol in men and
Correspondance to: Robert Lewis
Consultant Nephrologist, Wessex Regional Renal and Transplant Unit, Port-
smouth, PO6 3LY, UK.
S Afr J Diabetes Vasc Dis
2010;
7
: 13–15
Table 1.
Comparison of three tests for proteinuria
ACR
(mg/mmol)
PCR
(mg/mmol)
Dipstick
Normal
<
2.5 (males)
<
3.5 (females)
<
15
Negative
Microalbuminuria 2.5–30 (males)
3.5–30 (females)
Inappropriate
Negative
Macroalbuminuria
(clinical proteinuria)
>
30
>
50
+
/
++
ACR
=
albumin:creatinine ratio; PCR
=
protein:creatinine ratio
Robert Lewis
