A New Approach to Understanding the Therapeutic Potential of PRP and BMC: The Method of Ratios and Hemoanalytic Data – Part Two

Special guest post from David C. Karli, MD MBA introduces the concept of the method of ratios.

David C. Karli, MD MBA
David C. Karli, MD MBA

I started in the last post to review parts of the talk I gave at the TOBI conference on June 10th, which covered my approach to providing quality-controlled PRP and BMC preparations as a part of my regenerative medical practice at The Steadman Clinic. During the talk, I walked the audience through the essential features of obtaining hemoanalytic data on each and every autologous patient treatment preparation. I also provided additional background details on how I utilize hemoanalytic data to guide me in assessing the therapeutic potential of the PRP and BMC preparations I implant into my patients. I would like to finish off the review of my TOBI talk by introducing the concept of the method of ratios.

Although I have been looking at hemoanalytic data of PRP and BMC preparations for more than seven years, tracking the five critical parameters I mentioned in the previous post can be a challenge, especially if you are trying to balance the positive therapeutic component—platelets—with potentially negative components like RBCs, WBCs and/or Neutrophils. So, what can physicians do to categorize the PRP (or BMC) preparations they are starting to use in their clinic?

If you review the literature, you will find a couple of references that have proposed ways to categorize PRP preparations. Mishra, et al. offered the following strategy for categorizing PRP preparations:

A slightly different approach was outlined in a paper by Maunter, et al., in which the authors proposed the following scheme:

Both approaches rely on making binary assessments of the composition of the PRP. For example, Mishra’s Type 1 PRP has increased WBCs over baseline, while Type 3 has minimal or no WBCs. In the Mautner et al. approach the leukocyte content is characterized as above or below a level of 1%, which also applies to RBCs. The authors also highlight the need for clinicians to provide in their clinical publications the total number of platelets that were injected.  

Thus, the approaches touted in these two papers depend on having hemoanalytic data, but ignore the detailed information of actual component counts in a specific PRP preparation, in favor of categorizing the PRP into mostly binary bins. The problem with degrading the information content is that a PRP preparation with 110% of WBCs over baseline is tagged as the “same” type of PRP preparation that has 300% WBCs over baseline. Thus, the binary approach blurs what could be critical differences in therapeutic effectiveness of PRP preparations resulting from differences in composition. Another problem is that neither approach accounts for the inherent variation in composition that real patients’ PRP contain. For example, some preparations might have really high platelets, with a moderate level of RBCs or Neutrophils, while another patient’s PRP might have moderately high platelets, but virtually no RBCs or Neutrophils. Without measuring the various levels of the components, it isn’t possible to begin to tease apart the role each component plays in the therapeutic potential of the patient’s preparation.

So, what is a physician to do?

As presented at TOBI, I reviewed a concept we are calling the method of ratios. Our approach relies on hemoanalytic data in order to calculate the following ratios for PRP:

The method of ratios approach has the following features:

  • Each ratio directly relates the platelet number (the positive therapeutic element in PRP) to the potentially negative elements of RBCs, WBCs or Neutrophils.
  • A ratio’s value reflects the actual number of platelets present per unit RBC, WBC or Neutrophil.
  • The value of these ratios can be greater than one, equal to one or less than one.
  • Ratios are continuous in value (within physiological limits), in contrast to the binary approaches that only allow a parameter to take on two states.
  • The method of ratios applies to PRP and other biological fluids, like BMC or SVF, that are composed of cells.

During the TOBI talk, I presented several plots of ratios determined for PRP preparations (n = 32) and BMC preparations (n = 57). I will share with you the PRR and PRN plots to give you an idea of what real-world ratios look like for my PRP data set. Keep in mind that every PRP preparation I use is RBC/WBC-reduced, so all of the PRP preparations in the data were processed with the same protocol.

What is shown are the values of PRR and PRN plotted versus the total platelets of each of 32 PRP preparations. The linear regression lines are illustrative only, since neither line is statistically different from a slope of zero, and the correlation coefficient is less than 0.1 in both plots. A negative slope in a plot of ratios means that at higher ratio values, the level of platelets recovered goes down, as is hinted at in the PRR plot. What is intriguing about the PRN plot is that the regressed slope is virtually equal to zero. A zero slope means that recovery of platelets isn’t influenced by the PRN value. I think this implies that neutrophils separate differently or possibly more efficiently from platelets compared to RBCs in the manual protocol used to create the PRP. Most importantly, the method of ratios offers a way to leverage a patient’s hemoanalytic data, thereby giving insight into the role the components play in setting the regenerative potential of PRP or BMC for that patient. I’m confident that trends to boost the regenerative potential of PRP and BMC will emerge as the method of ratios is more widely adopted.

I don’t want to overstate the conclusions based on these two plots, but clearly values for PRP ratios can vary widely, and not just because of the varying input volumes of whole blood processed to produce the PRP. This variability suggests that the method of ratios reflects the complexity of a patient’s preparation, much like a fingerprint, and like a fingerprint, the unique set of ratios could serve to characterize the therapeutic potential of a patient’s PRP or BMC just prior to treatment. Consequently, the method of ratios provides a clinician with what I believe is a less cumbersome view of the critical components in PRP and BMC, and how the components relate directly to one another. 


“This variability suggests that the method of ratios reflects the complexity of a patient’s preparation, much like a fingerprint…”


I believe the method of ratios is a step forward in understanding the interplay of the various components in PRP in terms of a therapeutic potential. Furthermore, we plan to continue our efforts to refine the platform of quality-controlled hemoanalytics of PRP and BMC in order to aid clinicians as they seek to optimize their practice of regenerative medicine.

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