Fecal alpha-1 proteinase inhibitor (α1-PI) in dogs

What it shows

α1-PI is a blood protein that inhibits protein-cutting enzymes, and its molecular weight is similar to that of albumin. In diseases that make the intestine lose protein, the two are lost at about the same rate. Albumin is digested in the gut; α1-PI is not, so its amount in feces reflects how much plasma protein has leaked into the intestine.

The test is useful for early detection: fecal α1-PI can rise before clinical signs appear and before blood albumin or total protein fall. It also helps tell protein loss through the gut from liver causes of low albumin. Higher values are found in dogs with more marked changes in intestinal biopsies.

Directly measuring protein loss into the gut with a labelled-albumin method is impractical in everyday practice, so PLE is most often diagnosed by excluding other causes of low albumin. Fecal α1-PI is one of the few direct markers, but the three-day sampling and possible false-negative results limit its use.

Higher than reference — what it may be a sign of

• Protein-losing enteropathy — plasma protein leaks into the intestine. The most common causes in dogs are chronic inflammatory enteropathy and intestinal lymphangiectasia (a disorder of the gut’s lymph vessels), alone or together. Infectious, neoplastic and ulcerative disease, chronic intestinal obstruction and other lymphatic disorders can also cause PLE.
• Young age — healthy puppies can have increased values, so the adult reference interval does not apply to them.

A raised result says that protein is being lost through the gut, not why. The cause is looked for separately.

Lower than reference

A low or in-range value is the expected result in a healthy adult dog. It does not rule PLE out: results within the reference interval are possible in dogs with the disease, and false negatives are a recognised limitation. Daily amounts fluctuate considerably, which is why three days of stool are tested rather than one.

Look at together with

• Albumin — low albumin is the hallmark finding of PLE, but it is not specific and has many other causes.
• Globulin — low albumin and low globulin together (panhypoproteinemia) strongly suggest PLE, because kidney and liver causes do not explain both.
• Cholesterol — may be low in dogs with PLE; low calcium, low magnesium and few lymphocytes can also be seen.
• Urine protein : creatinine (UPC) and bile acids — check the other ways albumin can be lost or not made: through the kidneys or because of liver disease. Hypoadrenocorticism and blood loss are also excluded.

Units and conversion

Fecal α1-PI is reported in µg/g — micrograms per gram of feces. The laboratory gives a value for each of the three samples and their mean. There is one unit, so nothing needs converting; in the app each row keeps the value and unit printed on the form.

Reference range

The reference range is on your lab’s form. The assay is offered by few laboratories. The Texas A&M Gastrointestinal Laboratory gives a reference interval of 2.8–18.7 µg/g for dogs over 12 months, and considers abnormal a three-day mean of 13.9 µg/g or more, or any single sample of 21.0 µg/g or more. The three-day mean has its own, lower cut-off (13.9), so a mean can be abnormal even though it lies inside 2.8–18.7. A result in range does not exclude PLE.

Cats and dogs

Sources

1. Texas A&M Gastrointestinal Laboratory — Fecal Alpha1-Proteinase Inhibitor (α1-PI).
2. Schmid SM. Decoding Canine Protein-Losing Enteropathy. Today’s Veterinary Practice, July 2026.
3. Knoll JS. Canine & Feline Inflammation: Top 5 Biomarkers to Look For. Clinician’s Brief, May 2026.
4. Collier A. Chronic Enteropathies in Small Animals. Merck Veterinary Manual, professional version, full review August 2025.