Exceeding the Renal Threshold

Once the renal threshold has been exceeded, myoglobin can then precipitate in the renal glomerular filtrate leading to tubular obstruction and renal damage.

Myoglobin injures tubules in 3 ways:

• Forming casts, along with uric acid, and causing direct tubule obstruction leading to sludging and acute tubular necrosis
• Pigment induced intrarenal vasoconstriction occurs decreasing glomerular filtration rate (GFR) by scavenging nitrous oxide from the microcirculation
• Direct haem protein induced cytotoxicity

The GFR is also reduced in rhabdomyolysis by increased sympathetic tone, decreased prostaglandin synthesis and increased levels of Anti-Diuretic Hormone (ADH).