DIABETIC RENAL DISEASE (DIABETIC NEPHROPATHY)
It is most
common in type 1 diabetes. Some 20-30% of patients with type 1 diabetes will
develop renal disease (15-25 years after diagnosis). It is less prevalent in
type 2 diabetes (only 10-20% lifetime risk).
HYPERFILTRATION AND MICROALBUMINURIA
The earlier
symptoms of diabetes includes hyperfiltration (with urine albumin excretion,
UAE, <30mg/24 hour or 20µg/min) followed by progression through
microalbuminuria to proteinuria (UAE>300 mg/24 h or 200µg/min). After this
GFR falls and progress to ESRF. The first and best opportunity to detect the
disease clinically is at the stage of microalbuminuria. Dip-stick testing or
urine is not usually positive at such concentration of albumin and detection
relies on either 24 h quantitation or more conveniently the use of
albumin/creatinine ratio (normal <2.5 mg/mmol in men and <3.5 mg/mmol in
women) on at least two out of 3 separate urine specimens over a 3-6 month
period can be done. Due to day to day variation of UAE rates 2 of 3 samples
should be positive for the diagnosis. Microalbuminuria is not just a risk
factor of nephropathy but an independent risk factor for CAD (one of the most
potent risk factors known), being also associated with dyslipidaemia,
hypertension, endothelial dysfunction and diabetic retinopathy.
TYPE 4 RENAL TUBULAR ACIDOSIS
Hyporeninaemic
hypoaldosteronism may be a manifestation of diabetic nephropathy. It presents
with hyperchloraemic, hyperkalaemic metabolic acidosis. Failure of renin to
rise in response to posture or sodium restriction suggest an interstitial
(juxtaglomerular) defect. The failure of aldosterone release to be stimulated
directly by resulting hyperkalaemia suggest the possibility of dysfunction of
adrenal zona glomerulosa.
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