2010A11 Describe the changes that occur in the urine and the plasma with renal dysfunction.

Definition

·  Inability to maintain normal fluid and electrolyte homeostasis

Cause

·  Hypoperfusion

·  Outflow obstruction

·  Damage to glomerulus: T2DM, HTN, GN

·  Damage to tubule: ATN

·  Damage to interstitium: drugs

Water

·  Expanded ECF volume, APO if oliguric or anuric

Electrolytes

·  ↑[K⁺] (high risk esp if oliguric)

·  ↑[H⁺]: HAGMA (PO₄^3-, SO₄^2-) or NAGMA (RTA)

·  ↓[Ca²⁺], ↑[PO₄^3-], ↑[PTH], ↓[Vit D₃] – if chronic

·  ↑osmolality but no ↑tonicity (urea – small particle, ineffective osmole)

Waste

·  ↑Creatinine (only after 50% loss of nephron function; curvilinear rise)

·  ↑Urea (too variable to estimate degree of dysfunction; ↑if dehydration or high protein intake)

Other

·  ↓[Albumin] if nephrosis

·  ↓[Hb] if ↓[Epo]

Volume

·  Polyuria: e.g. post-obstructive diuresis

·  Oliguria: <0.5mL/kg/h (most common)

·  Anuria: <100mL/day (advanced)

Concentration

·  Inability to concentrate or dilute urine, regardless of urine volume

·  Often isotonic in advanced renal failure

·  Plasma 290mOsm, normal max 1200mOsm, normal min 50mOsm

Fractional sodium excretion

·  n(Na⁺) excreted / n(Na⁺) passing through tubule

·  <1%: pre-renal e.g. hypotension

·  >2-3%: intra-renal e.g. ATN

Abnormal contents

·  Protein (glomerular dysfunction)

·  Granular casts (ATN)

·  RBC casts (GN)