What test can confirm intestinal protein loss but does not differentiate the underlying cause?

• A. Urine protein electrophoresis
• B. Fecal alpha-1 proteinase inhibitor
• C. Serum albumin
• D. Serum trypsin-like immunoreactivity

Answer: (B)

The test is used to confirm protein loss from the gut, without indicating why the loss is happening. In protein-losing enteropathy, proteins leak into the intestinal lumen. Fecal alpha-1 antitrypsin (the fecal alpha-1 proteinase inhibitor) is a marker that is not degraded in the gut and is not removed by the kidneys, so its presence in stool reflects intestinal loss of protein. Measuring its amount (often via stool clearance) shows that the gut is losing protein, but it does not specify the underlying cause of that loss (such as inflammatory disease, lymphangiectasia, or infection). Other options don’t specifically quantify intestinal protein loss: urine protein electrophoresis looks at urinary proteins, serum albumin shows systemic protein status but not the source, and serum trypsin-like immunoreactivity relates more to pancreatic function than to intestinal protein loss.