Leaky gut, or increased intestinal permeability, is also known as a functional intestinal disorder at the site of nutrient absorption, known as the brush border, in the small intestine. 

For more details, see this article about leaky gut.

Currently, there is no clear gold-standard, reliable, cost-effective, and easy-to-perform laboratory evaluation for leaky gut; instead, a qualified physician primarily provides the diagnosis. 

While there is no perfect test for leaky gut, below are some tests your doctor can order to determine if leaky gut may be a contributing factor for you:

• Serum Zonulin
• Serum LPS antibodies
• Lactulose/mannitol test
• Anti-CdtB (cytolethal distending toxin B) and anti-vinculin antibody
• Serum actomyosin antibodies

Further, read this article written by Dr. Alisun Bonville for the deep science behind leaky gut and testing options.