This article is based on a conversation with Moichor Director of Pathology Kyle Webb, ​​DVM, DACVP (Clinical)

We’re excited to announce Moichor’s Reference Intervals (RIs) for the major commonly seen species. The list of the 36 new intervals includes psittacine intervals stratified for species size (i.e., small, medium, and large), as well as individualized intervals for our most commonly seen psittacines, including cockatiels, white cockatoos, and blue-and-yellow macaws. 

The latter is particularly exciting because reference intervals are most valuable when they are specific to the patient population.

For exotics, Moichor’s RIs are critical because many species lack quality literature  on their wellness ranges. Some of the intervals we are developing for our next quarterly RI release are species whose RIs have not been well studied, if at all. 

Seeing as many samples as we do, and with the variety of species we see, enables us to create reference intervals that were previously unknown and aren't readily available at other clinical lab providers.

How we build rigorous and robust reference intervals

Traditionally, to construct reference intervals, a “healthy” population of a species is selected by predefined wellness criteria, measurement is conducted, and finally a reference interval is derived. This requires a prohibitive amount of sampling effort and even then the selected population may include patients with subclinical diseases. 

Ideally, 120 healthy samples are recommended to create a robust clinical reference interval. This stringent standard allows for the effect of the small number of patients with subclinical diseases and outliners on the RIs to be neglected [1]. Nevertheless, that’s an extraordinary challenge for exotic species because many of these patients are not often seen well [2].

The American Society of Veterinary Clinical Pathology recognizes there are ways to calculate reference intervals whereby the minimum study population can be 40. There are also rules about when to use individual reference intervals versus group reference intervals [3]. 

To ensure the robustness of our RIs, we started by adding additional rigor to the sample intake process. Moichor’s process incorporates additional steps to select healthy samples by pre-screening samples submitted for wellness check. 

These wellness samples are subsequently screened by Moichor’s board-certified clinical pathologists for signs of microscopic abnormalities such as subtle toxic change to confirm the healthy status of study candidates.  Finally, a member of our clinical team randomly and continually follows up with clinics to confirm the patients included in the RI study didn't break with illness at, or soon after wellness visits.

Naturally, there are some species where having 40 healthy subjects is still a challenge, thus, our reference intervals are either individualized to the species or methodically grouped, based on factors like habitat, taxonomic relation, and lifestyle.

For instance, we have seen over 40 wellness tortoises as a whole, but have not yet seen 40 wellness tortoises of any one specific species. And so, we refer to the phylogenetic tree to see where they branched off, and decide if they are closely related enough to reasonably group them while we gather more individualized data.

These small group intervals, while not individualized to the species, are often much more useful than the RIs in the literature that were poorly constructed, oftentimes by using fewer than 20-25 individual subjects, much larger species subgroups, or created from zoo-housed animals rather than animals in a companion setting.

For species with fewer than the minimum number of individual healthy subjects, we still look to the most current literature. We constantly evaluate and study our reference intervals so when we hit population milestones, RIs will be reevaluated or derived to reflect our most current understandings. 

One of our ultimate goals is to provide high resolution RIs, fully controlled for confounding factors such as sex, life style, and stages of life. As part of that goal, we will always communicate to our clients when these intervals have been updated and those insights will also be reflected in the pathology reports provided.

Selected interesting findings

While building RIs using a large number of subjects, we noticed interesting trends that directly affect how clinical values can be interpreted by veterinarians.

We learned that low numbers of bands in certain birds are not necessarily something to worry about if the patient is otherwise healthy. This hasn’t previously been explored in the available literature, but was something that Dr. Kyle Webb, Moichor’s Directory of Clinical Pathology had suspected for a long time because it can also be true in mammals.

It was vindicating to see when we created reference intervals for these birds’ species. We were able to see that, zero to 200 or even 300 bands in a healthy bird can be normal as long as there's no evidence of toxic change. We’re excited to continue to track this even further as we continue to build these intervals.

We also learned that small psittacines, such as cockatiels, have lower heterophil counts in health than other bigger bird species. This is important because it illustrates that using generalized reference intervals (e.g. for all psittacines) does a disservice to smaller psittacines like cockatiels. Applying a reference interval to cockatiels that was derived from a group that included macaws gives a false impression of heteropenia where none exists.

Similarly we found that bearded dragons naturally have higher azurophil counts than other lizards and that’s just normal for them. 

Finally, despite chickens’ rising popularity as a companion bird, there is only a single other study in the literature that derived and validated biochemical reference intervals for chickens in a ‘backyard’ setting, and our backyard chicken hematologic intervals are the only validated ones available to our knowledge. 

We look forward to sharing more on these reference intervals quarterly and in a master class at ExoticsCon 2022.

Join us in building accurate and robust reference intervals 

This is the culmination of a couple of years of work. We are excited to have arrived at this point in time where we are able to process clinical data and construct accurate and robust clinical reference intervals for a wide variety of species. It’s something we have seen as a major goal and it feels like we’ve only just begun. 

The best way you can participate in building these intervals is by adding the sex, age, and weight when known, for each patient you enter into the Moichor system. This will help us to build the next stages of RIs, which accounts not only for species but also major physiological and lifestyle factors that affect patient reference clinical values. Your communication with us about the status of the patients before or after testing also plays an important role in the process.

Another way to help is to use the notes section to communicate the specific species when it’s not in the species selector. If it’s not in the species drop down select, it’s usually one we don’t have yet. Or if it's a subspecies that's not listed, let us know and we can add it right away. 

Reference intervals for Companion Pet 

A factor that makes Moichor Reference Intervals unique is the data is based on companion pets. In many cases reference intervals have been generated based on zoo populations because it’s usually zoos that publish these types of reference intervals.

In such cases, even species that might have published reference intervals wouldn't necessarily be applicable to our patient population, because they're all animals that are kept in a single zoo or a couple of zoos, or that are wild caught instead of being captive.

List of New & Updated Reference Intervals