Hi, This is my first time using this website and I have to say that it looks very helpful. I’m moving to the Innovance D-dimer (Siemens) and need to do a new normal range study. I was going to purchase a normal donor set from Precision BioLogic but they told me that they do not provide a set for normal range for D-dimer because this normal range should be done from fresh specimens and their products are frozen pheresis samples. My question, is it true that the normal range for the D-dimer must be done from fresh specimens? If not, where can I get a normal donor set to run my study?
Yexenia López, MT (ASCP)
Cambridge Hospital, Cambridge, MA
Hello Yexenia and welcome to the Fritsma Factor. You can develop your D-dimer normal range (aka reference interval) from frozen plasma specimens, but you have to collect them in your own hospital so they reflect your local patient age and demographics. You do not have to collect 120 specimens; 30 healthy subjects should be enough–15 males and 15 females. Once you have assayed all 30 and computed the mean and two standard deviations, compare the results to the reference interval Siemens provides in their package insert. For D-dimer, there is usually just a high-end limit. Your result should match Siemens by within ± 10%. If it matches, you can use Siemens’ cutoff, if not, you will need to publish your own cutoff. Be careful to duplicate Siemens’ units, as units vary among manufacturers and can create reporting confusion. The method for developing reference intervals is explained more fully in the audio module available on this web site, Method Validation in Hemostasis, Part 2.
When the specialty techs in our coagulation laboratory decide to collect specimens for reference intervals, they put the word out to all the lab techs, hospital personnel, residents, and students. We pay $10 a tube, so it is pretty easy to recruit. We collect several tubes from each healthy subject, centrifuge to make platelet-poor plasma, aliquot to multiple freezer tubes, label and freeze at -70°C. That way, we usually have a set of normals available to pull out of the freezer whenever we need to do a new reference interval. You probably won’t find a set of normal samples for reference interval determinations from manufacturers, as it is necessary to develop your own locally, though all manufacturers develop an interval in house that you may use for comparison.
I want to acknowledge Mr. Stephen Duff of Precision BioLogic for his assistance in responding to Ms. Lopez’ question.