What is ‘X-Factor’ When Discussing Platelet-Rich Plasma & Why Does it Matter?

Platelet-Rich Plasma (PRP) is an autologous concentration of human platelets suspended in a volume of plasma [1]. ‘X-Factor’ refers to the platelet concentration of platelet-rich plasma achieved over baseline whole blood values. Platelets specifically are of interest as they are responsible for advancing, enhancing and regulating the healing response within the body [1].

How to calculate the X-Factor

To calculate the ‘X’ or Concentration Factor of platelets in a PRP sample, a hematological analysis must be performed on the baseline (whole blood) and concentrated (PRP) samples. With this information, it is a simple calculation to determine the platelet concentration factor:

Platelet Count [PRP] Platelet Count [Baseline or Whole Blood] = Platelet Concentration

Example:

PLT [PRP] = 1,750,000/mm3

PLT [whole blood] = 250,000/mm3

1,750,000/mm3 / 250,000/mm3 = 7X Platelet Concentration

We have concentrated platelets 7 times baseline concentration in whole blood.

X-Factor can only be used as a comparison measure between different PRP preparation systems and protocols and this calculation does not take into account injectate volume and total dose of platelets delivered.

Why does X-Factor, injectate volume, and total dose of platelets delivered matter?

The concentration of platelets in a PRP sample is positively correlated to the growth factor and cell adhesion protein concentrations, critical to stimulating a healing and regenerative response [2]. This positive correlation of improved tenocyte proliferation and migration is observed up to 14x, favoring higher concentrated PRP over lower concentrated PRP [3]. Expanding on this, increasing platelet concentrations with PRP proves to be critical for helping regeneration (specifically tendon regeneration in aging patients in the cited study) [3].

Our previous blog post reviews in detail the dose-dependent response of PRP, which requires adequate concentration and volume of whole blood to achieve an optimal platelet dose for healing.

In short:

Achieving a high concentration but very low volume of PRP (resulting from a low volume of initial blood draw) will not allow you to capture the necessary dose of platelets to elicit a clinically meaningful response
Having a large volume of PRP but poor concentration (resulting from an efficient processing system) will not allow you to deliver the necessary dose of platelets to elicit a clinically meaningful response

Achieving the ideal platelet concentration and delivery volume matters because underdosed PRP will lead to poor results, as evidenced in the table below. PRP should concentrate platelets to at least 5X baseline values to meet the minimum requirement of what is considered PRP [4].

The product used in the Bennell Study was 3 intra-articular injections of 5 mL of RegenLab PRP, performed at weekly intervals under ultrasound guidance using a medial patellofemoral approach [5]. The paper describes the product ranging from 1.6-5X from whole blood platelet levels and is leukocyte poor [5]. eTable 2 (Summary of PRP Characteristics Based on Reporting Recommendations) reports the mean platelet volume as 325x106/mm3. One of their exclusion criteria is a whole blood platelet count of less than 150x106/mm3 [5]. At best, their PRP was concentrating platelets 2X baseline levels. Other studies comparing various commercial PRP kits report RegenLab PRP to perform worse than 2X, with actual concentration ranging from 0.5-1.6X baseline whole blood platelet levels [4].

To highlight the importance of how a concentrated PRP product will obtain clinically meaningful and positive results:

How to Ensure Optimal Dosing of PRP?

One effective way to ensure optimal dosing of PRP is to utilize a validated commercial kit. EmCyte PRP (specifically the neutrophil-poor preparation of the GS60 PurePRP II), consistently provides a 7X PRP and about 13 Billion platelets in a 7 mL sample [9]. This would satisfy the established consensus definition of PRP from a platelet concentration factor and dose standpoint. More info here.

In addition, it is vital to understand the total dose of delivered platelets and establish platelet concentration at the point of injection. The Horiba Micros 60 Hematology Analyzer is universally recognized for reliability, high platelet range (4 million platelets/ µL) and ease of use to characterize Platelet Rich Plasma (PRP) in less than 1 minute. If you’re not ready to invest the time and resources in maintaining intensive lab equipment, Plymouth Medical’s PAC Service is the perfect solution. All the necessary tools and supplies for a baseline and PRP sample analysis are provided. The PAC service is the first and only characterization service offering complete PRP cell analysis and classification in an easy-to understand report resulting in meaningful interpretation of clinical outcomes.

Any Questions? Contact Us

Citations

[1] Marx, Robert E. “Platelet-Rich Plasma: Evidence to Support Its Use.” Journal of Oral and Maxillofacial Surgery, vol. 62, no. 4, 2004, pp. 489–496.,https://doi.org/10.1016/j.joms.2003.12.003.

[2] Verma, Rahul, et al. “Factors Affecting the Quantity and Quality of Platelet-Rich Plasma and Platelet-Derived Growth Factor-BB: An Observational Study.” Journal of Bio-X Research, vol. 4, no. 2, 2021, pp. 67–70., https://doi.org/10.1097/jbr.0000000000000091.

[3] Berger, D. R., et al. “Platelet Lysates from Aged Donors Promote Human Tenocyte Proliferation and Migration in a Concentration-Dependent Manner.” Bone & Joint Research, vol. 8, no. 1, 2019, pp. 32–40., https://doi.org/10.1302/2046-3758.81.bjr-2018-0164.r1.

[4] Magalon, Jeremy, et al. “Technical and Biological Review of Authorized Medical Devices for Platelets-Rich Plasma Preparation in the Field of Regenerative Medicine.” Platelets, vol. 32, no. 2, 2020, pp. 200–208., https://doi.org/10.1080/09537104.2020.1832653.

[5] Bennell, Kim L., et al. “Effect of Intra-Articular Platelet-Rich Plasma vs Placebo Injection on Pain and Medial Tibial Cartilage Volume in Patients with Knee Osteoarthritis.” JAMA, vol. 326, no. 20, 2021, p. 2021., https://doi.org/10.1001/jama.2021.19415.

[6] Kearney, Rebecca S., et al. “Effect of Platelet-Rich Plasma Injection vs Sham Injection on Tendon Dysfunction in Patients with Chronic Midportion Achilles Tendinopathy.” JAMA, vol. 326, no. 2, 2021, p. 137., https://doi.org/10.1001/jama.2021.6986.

[7] Bansal, Himanshu, et al. “Platelet-Rich Plasma (PRP) in Osteoarthritis (OA) Knee: Correct Dose Critical for Long Term Clinical Efficacy.” Scientific Reports, vol. 11, no. 1, 2021, https://doi.org/10.1038/s41598-021-83025-2.

[8] Wu, Zutong, et al. “Application Effect of Different Concentrations of Platelet-Rich Plasma Combined with Quadriceps Training on Cartilage Repair of Knee Osteoarthritis.” Journal of Healthcare Engineering, vol. 2022, 2022, pp. 1–8., https://doi.org/10.1155/2022/7878064.

[9] Mandle, Robert, et al. “Comparisons of EmCyte PurePRP II, Harvest/Terumo APC60/Clear PRP, and Arthrex Angel PRP Products” (2015)

04/15/22

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