A “MAT test” refers to different things depending on the context. The two most common meanings are the Microscopic Agglutination Test, a blood test used to diagnose a bacterial infection called leptospirosis in both humans and animals, and the Miller Analogies Test, a graduate school admissions exam that was retired in 2023. Here’s what you need to know about each.
The Microscopic Agglutination Test for Leptospirosis
The Microscopic Agglutination Test is the gold standard laboratory test for diagnosing leptospirosis, a bacterial infection spread through the urine of infected animals. It works by mixing a patient’s blood serum with live samples of Leptospira bacteria. If the patient has antibodies against the bacteria, those antibodies cause the bacteria to clump together into visible clusters. A technician then examines these clusters under a special dark-field microscope at 100x magnification.
What makes the MAT unique is its ability to identify the specific strain involved. Each blood sample is tested against a panel of different bacterial strains, often 20 or more. The lab records which strain causes the strongest clumping reaction and at what dilution of the blood sample. This tells doctors not just whether you have leptospirosis, but which variety of the bacteria is likely responsible.
How MAT Results Are Interpreted
Results are reported as a titer, which is the highest dilution of blood serum that still causes at least 50% of the bacteria to clump together. A titer of 1:100 or higher is generally considered a positive result, meaning antibodies are present. However, a positive result at 1:100 doesn’t necessarily confirm an active infection. It could reflect a past exposure or, in animals, a recent vaccination.
Titers of 1:1,000 or higher are much more telling. At that level, especially when an animal or person is showing symptoms, clinicians treat the result as strong evidence of active leptospirosis. The U.S. Animal Health Association established this framework back in 1977, and it remains the standard interpretation today.
Because a single blood draw can be hard to interpret on its own, the most reliable approach is paired testing. This means drawing blood twice, spaced two to six weeks apart, and comparing the results. A fourfold rise in titer between the two samples is considered the clearest confirmation of a current infection. Cornell University’s veterinary diagnostic lab specifically recommends this paired approach over relying on any single result.
Timing Matters for Accuracy
The MAT has a significant blind spot during the first days of illness. Your immune system needs time to produce enough antibodies for the test to detect, and that process typically peaks around 8 to 14 days after symptoms begin. In studies on dogs, most animals showed detectable antibody levels by day 7 after exposure, with peak levels between days 10 and 14.
During the earliest phase of leptospirosis (the first 3 to 8 days), the MAT catches a relatively small percentage of cases. One study found it detected only 12% of confirmed cases during this acute window, compared to 74% for PCR testing, which looks for the bacteria’s genetic material directly. This is why many clinicians use PCR early in the illness and reserve the MAT for confirmation once enough time has passed for antibodies to develop. The two tests complement each other: PCR works best early, while the MAT becomes more reliable as the immune response builds.
MAT in Veterinary Medicine
Veterinarians rely heavily on the MAT, particularly for dogs and livestock. Leptospirosis is a common concern in dogs that swim in ponds, walk through wet areas, or have contact with wildlife. The challenge in veterinary settings is that many dogs are vaccinated against leptospirosis, and vaccination itself produces antibodies that can trigger a positive MAT result. Distinguishing a vaccine response from a true infection requires looking at the specific strains that react, the height of the titers, and whether titers are rising over time.
In pig herds, the same interpretation principles apply. A few animals with titers at 1:100 might simply reflect past exposure or vaccination. But if most of the herd shows titers at 1:1,000 or above alongside clinical signs like reproductive problems or kidney issues, that points strongly toward active disease circulating in the group.
The Miller Analogies Test (Now Retired)
The other well-known MAT was the Miller Analogies Test, a standardized exam once used for graduate school admissions. It consisted of 120 analogy questions to be completed in 60 minutes, testing your ability to recognize relationships between ideas across four broad areas: humanities, natural sciences, mathematics, and social sciences. Unlike the GRE, which tests reasoning through multiple question types, the Miller Analogies Test relied entirely on analogies as its format.
Pearson, the company that administered the test, officially retired the Miller Analogies Test on November 15, 2023. It is no longer available to take. As of November 15, 2024, official transcripts and personal score reports from previous test sessions are also no longer available. If you previously took the MAT for a graduate program application, those scores can no longer be sent to institutions. Programs that once accepted MAT scores now typically require the GRE or have moved to test-optional admissions.