From Joanna Carroll:
What recommendations would you make for veterinary medicine? I work at the North Carolina State University College of Veterinary Medicine Veterinary Teaching Hospital. We just purchased a new automated coag analyzer, the Stago STA Satellite. Currently we have the semi-automated STart 4 by Stago. We have not been using Stago reagents, but we will probably switch to their prothrombin time (PT) reagent and use their calcium chloride for partial thromboplastin time (PTT). If our comparisons are close, can we adjust our current ranges or should we reestablish new?
It is not feasible to acquire normal samples from 60 dogs, cats, and horses in a week, as we have to ask people to bring their pets in, or draw blood at home and bring it in. It is also very difficult to get enough blood to have 5-10 aliquots from each sample. We can manage to get around 30 samples from dogs, sometimes 20 or so from horses. We do want to follow protocol as much as possible, as we pride ourselves in accurate results.
Thank you for your time.
Joanna Carroll MT (ASCP)
Clinical Pathology Lab
NCSU College of Veterinary Medicine
Hello, Joanna, and thank you for your question. Where normal ranges exist, you can legitimately use a confirmatory approach, which typically specifies 20 aliquots from normal subjects. Assay the specimens, compute mean and 95% confidence interval or ±2 SD, compare to the existing normal range, and adjust if necessary. Only if the new normals differ significantly, for instance by >20%, would you want to establish a new normal range from scratch.
In instances where normal aliquots are difficult to collect, for instance, when establishing pediatric values in human medicine, published reference intervals are a reasonable substitute, though slightly less accurate. The key is to establish at what point does an abnormal value trigger intervention.
This is the first question we’ve had on the topic of hemostasis in veterinary medicine, and I would be interested to learn how other veterinary labs establish normals, and also to learn are the most common applications for PTs, PTTs, and other hemostasis tests.