Plasma albumin concentration is calculated as: intravascular albumin mass / plasma volume
Causes of decreased plasma albumin:
1. Decreased synthesis.
2. Increased catabolism [very slow]
3. Increased loss:
Exudative loss in burns
Increased capillary permeability (leakage into the interstitium)
Decreased lymph clearance.
“Capillary leak syndrome” occurs in systemic inflammatory response syndrome. Due to widespread damage to the capillary endothelium, there is increased loss of medium to high molecular weigh compounds, particularly albumin, into the extravascular space and therefore loss of the normal Starling relationship.
Hypoalbuminemia is associated with liver and renal disease, PET, SIRS / including burns, trauma. Low preoperative albumin is an indicator of poor outcome from surgery.
Albumin is a poor marker of liver dysfunction; prothrombin time is more reliable.
Albumin loss occurs in nephropathies (nephrotic syndrome).
There is a small loss of albumin in dialysis circuits.
In normal pregnancy there is an increase in plasma volume. In PET there is a paradoxical decrease in plasma volume, widespread capillary leak and albuminuria.
Interleukins cause a marked decease in synthesis of plasma proteins other than albumin.
In fact Albumin and Transferrins decrease in the stress response, a process often termed "negative acute phase proteins".
IL6 directly decreases the expression of albumin messenger RNA.
Overall, the picture in the stress response is:
1. Initial decrease in albumin associated with increase in acute phase proteins.
2. Subsequent global increase in hepatic protein synthesis; including albumin.
There is massive protein loss from the burn site & increased vascular permeability & decreased albumin synthesis & protein losing nephropathy. The use of albumin in patients with >15% burns after 24 hours has been recommended.
In trauma there is increased redistribution and transcapillary escape of albumin.
Decreased serum albumin preoperatively is an independent indicator of poor outcome.
SIRS - associated with increased capillary permeability, due to the effects, amongst others, of bacterial endotoxin and cytotoxic T cells. In sepsis there is a profound reduction in plasma albumin associated with marked fluid shifts.
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