My boss, Dr. David Karli, introduced the concept of the method of ratios during a talk he gave at the TOBI conference this past June. He wrote a couple of guest posts for the Blog in which he covered the field of hemoanalytics and how, in the case of PRP, a set of ratios might be useful as a kind of “fingerprint” of a specific patient’s PRP preparation. See his posts (Part One and Part Two) for a brief introduction to the method of ratios. I would like to extend our review of the method of ratios to PRP samples made by various commercial device technologies.
In Part Two of his posts, Dr. Karli presented plots of platelet-to-RBC and platelet-to-Neutrophil ratios (x-axis) versus Total Platelets (y-axis). These plots showed a fair amount of scatter, which we think supports our view that a set of ratios (the other ratio is platelet-to-WBC) might serve as a therapeutic fingerprint of the patient’s PRP preparation. Thus, physicians using quantitative, hemoanalytic data would quickly be able to obtain the values of the ratios on the preparation that is about to be injected.
By tracking ratios and clinical outcomes, a physician should be able to build a profile of what looks like a therapeutically beneficial preparation for a particular application.
Greyledge has launched an app to facilitate calculating ratios, which is available for a fee on the App Store and the Google Store. Of course, you could just use a calculator, but it isn’t as slick.
While not a primary focus of ours, the method of ratios could be used to characterize commercial device technology being sold to produce PRP (or BMC, for that matter, since the method of ratios can be applied to BMC hemoanalytic data). In a happy coincidence for us, a paper was published by Degen, et al. earlier this year in which the authors ran several commercial systems sold for producing PRP with seven unrelated blood donor samples. The PRP samples were analyzed for Platelets, Neutrophils, RBCs, WBCs and output volume, among other parameters. Each of the whole blood samples was divided up and processed according to the manufacturer’s instructions, so some of the systems involved a single spin and some involved double-spin protocols. The individual results were averaged together, and summarized in Table 2 of Degen, et al. (2017). It also was possible to calculate an average number of Plts present in the output PRP from the data reported by Degen, et al.
Given this data set, we were able to calculate ratios for Plt/RBC (PRR), Plt/WBC (PRW) and Plt/NEU (PRN) for the six commercial systems tested by Degen, et al. The PRN and PRR values were plotted, as follows:
A couple of points of interest emerge from the use of the method of ratios with device performance data. First, the Arthrex Angel system, touted for its ability to substantially reduce RBCs (e.g., 2% Hct, S-1), produces a good ratio for PRR, but in this study it produced the lowest total yield of platelets among the methods studied. This suggests that a high PRR value probably is achieved at the expense of providing fewer platelets, which is borne out when you look at the 7% Hct value in the Angel system (S-2). The 7% Hct setting obviously contains more RBCs, but the yield of total platelets went up for the 7% Hct setting for the Angel system. However, the PRR value dropped dramatically for the higher Hct setting compared to the 2% Hct ratio value. Overall, it seems that the devices producing higher total platelets also contain higher levels of RBCs, which is reflected in their lower PRR values.
The PRN data also is interesting. Notice the tightness of S-2 and S-6 in the PRR plot, but on the PRN plot the points have separated quite a bit. It would seem that neutrophils are more easily separated from platelets in the Angel system compared to the Biomet system, since the PRN values are quite different. Yet, the separation of RBCs is similar, given the two systems’ similar PRR values. This observation hints at the possibility that the device design itself, along with the physical processing might influence the separation efficiency of the various components, such that RBCs and Neutrophils don’t behave the same in every device technology despite the similarity in their cellular densities.
As indicated in the legend, S-7 represents the averaged values of 32 PRP preparations produced in a manual process by Greyledge at The Steadman Clinic, as requested by Dr. Karli in treating his patients. The manual method used is designed to reduce RBCs and WBCs/NEUs, which is supported by the fact that both the PRR and PRN values are quite high compared to the device technologies. The manual method also yields a respectable number of platelets, with the average concentration of platelets at just over 1,000,000/µL, as Dr. Karli reported during his TOBI talk.
While Dr. Karli and I think the true value of the method of ratios for PRP lies in its ease of characterizing the therapeutic status of a patient’s specific treatment preparation (i.e., its fingerprint), there is some value to applying ratios to the averaged output of commercial device technologies, as shown above.
This type of analysis could help physicians make better informed decisions when trying to adopt a PRP-generating device technology for use in their clinic.