How does low albumin contribute to edema formation?

• A. Decreased oncotic pressure
• B. Increased capillary hydrostatic pressure
• C. Increased lymphatic drainage
• D. Increased capillary permeability

Answer: (A)

Low albumin lowers the plasma oncotic (colloid) pressure that pulls fluid back into the capillaries. With weaker oncotic pull, more fluid filters out into the interstitial space and is not drawn back into the vessels, so fluid accumulates and edema forms. This is common in states where albumin is depleted, such as liver disease, nephrotic syndrome, or malnutrition. Other pathways can also cause edema—higher capillary hydrostatic pressure from venous congestion pushes more fluid out, and increased capillary permeability lets protein and fluid leak into tissues—but the direct effect of low albumin is a reduced oncotic force that favors edema. Increased lymphatic drainage would tend to remove excess fluid, not create edema.