Running analyses on trusted in-house chemistry analyzers is integral to any veterinary practice. Having ready access to these results can help facilitate prognoses and conversations with patients' families. However, what happens when a practice compares in-house results to readings conducted at a veterinary reference laboratory like Moichor? Spoiler alert — there's going to be a difference in results.

When veterinarians receive varying objective data from different chemistry analyzers, it's common to question the diagnostic testing accuracy in each. In the worst case, a vet might doubt the level of accuracy in results and not feel confident with their patient diagnosis and patient care.

So what's going on? Is there a problem in one of the blood samples? Could a machine be lacking calibration? Were human errors involved at the veterinary reference laboratory? Why are the results of the house laboratory testing different from what I'm getting back from Moichor?

Here's the good news: everything is fine!

Many chemistry analyzer manuals have a notice stating that running a side-by-side is not recommended. There's a very simple explanation for this fact: Chemistry analyzers use different methods for measuring chemistry.

In fact, your chemistry results from Moichor are likely more accurate than many other analyzers due to different methodologies between machines and reference intervals (RIs) used to compare results.⁽¹⁾

Machine methodology differences

One reason why results between chemistry analyzers dramatically diverge is because each system employs different chemical reactions to deliver results.

For instance, the Beckman AU680 uses a reaction to measure AST (aspartate aminotransferase) that consists of a single elementary step and final product.⁽²⁾ In contrast, other devices use a reaction with multiple intermediate steps to get to the final product.⁽¹⁾

In the analyzer manual for the Catalyst Chemistry analyzer, it even states, “Comparing results from different laboratories that may be using different equipment or methods is imprecise at best.” ⁽¹⁾

In essence, commercial and clinical laboratories establish their own species reference ranges for the equipment and methodology used and the same holds true for benchtop chemistry analyzers. ⁽¹⁾

Reference intervals

Another reason why results differ between analyzers is because of RIs. Study populations used by many other reference labs to create reference intervals can be small and not reflect the population as a whole. As a result, species may be grouped into larger categories clouding information that is species specific. Moreover, each published reference interval is specific to each chemistry analyzer.

While it's difficult to paint all reference labs with the same brush, we can tell you that at Moichor we are actively building reference intervals with a goal to be as species specific as possible. Take for example the image below:

An analyzer from a different company has grouped Gallus domesticus & Meleagris gallopavo together to create an RI for the genre, whereas Moichor has separated them specifically to create a more reliable sample population.

All RIs published by Moichor requirements set forth by the American College of Veterinary Pathologists .(3) Many of these RIs are species specific and all have strong, verified study populations. For RIs that are not published in-house yet, they are sourced from reputable peer-reviewed literature and are applied as taxonomically specific as possible. This is an ongoing project that is updated regularly.

Conclusion

Both chemistry analyzer methodologies and RI study populations are responsible for variations seen in results, but this can be surprising for some animal healthcare providers as they are often trained using only the hospital laboratory specifically from their studies. As a result, the issue of interpreting results between in-house analyzers and reference laboratories is not generally encountered until practice whether that entails feline patients, routine blood chemistry, or disease in dogs.

The best way to start learning where things may be different is to recognize the result and RI differences specific to different methodologies. For chemistry evaluations, using a familiar patient can help elucidate where the differences may arise between in-house analyzers and reference lab machines.

References: 

1. IDEXX. “Catalyst DX Operators Guide - Home - IDEXX US.” Catalyst DX Operators Guide, https://www.idexx.com/files/catalyst-dx-operators-guide-en.pdf. 
2. Beckman Coulter. “Aspartate Aminotransferase (AST) - Beckman Coulter.” AST, https://www.beckmancoulter.com/wsrportal/techdocs?docname=/cis/BAOSR6x09/%25%25/EN_. 
3. Friedrichs, Kristen R., et al. “ASVCP Reference Interval Guidelines: Determination of De Novo Reference Intervals in Veterinary Species and Other Related Topics.” Veterinary Clinical Pathology, vol. 41, no. 4, 2012, pp. 441–453., https://doi.org/10.1111/vcp.12006.