The influence of environmental variables on platelet concentration in horse platelet-rich plasma, 2016, Rinnovati et al

Abstract
Platelet-rich plasma (PRP) commonly refers to blood products which contain a higher platelet (PLT) concentration as compared to normal plasma. Autologous PRP has been shown to be safe and effective in promoting the natural processes of soft tissue healing or reconstruction in humans and horses. Variability in PLT concentration has been observed in practice between PRP preparations from different patients or from the same individual under different conditions. A change in PLT concentration could modify PRP efficacy in routine applications. The aim of this study was to test the influence of environmental, individual and agonistic variables on the PLT concentration of PRP in horses.

Six healthy Standardbred mares were exposed to six different variables with a one-week washout period between variables, and PRP was subsequently obtained from each horse. The variables were time of withdrawal during the day (morning/evening), hydration status (overhydration/dehydration) treatment with anti-inflammatory drugs and training periods on a treadmill. The platelet concentration was significantly higher in horses treated with a non-steroidal anti-inflammatory drug (P = 0.03). The leukocyte concentration increased 2–9 fold with respect to whole blood in the PRP which was obtained after exposure to all the variable considered. Environmental variation in platelet concentration should be taken into consideration during PRP preparation.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4932754/
open access

 

I found this paper when I was thinking about what might be causing the finding of microclots in some of the ME/CFS and LC samples.

The fluid that is being used is platelet-poor plasma, not the platelet rich plasma here. But there may still be contents in the plasma, that could influence the ability of the solids to separate out in the centrifuge, and for residual solids to subsequently form microclots.

See this figure for example:


Use of NSAIDs increased the platelet concentration in the PRP. Exercise reduced the platelet concentration.
Dehydration increased the platelet concentration. Hydration reduced it.
Even time of day of collection had an impact. If your disease population is more likely to have an afternoon collection rather than a morning collection, that might bias outcomes.

And it's not just the platelets. The concentration of white blood cells is affected by environmental factors such as dehydration.

 

All of the environmental factors tested here could conceivably be different in cohorts of ME/CFS/LC versus healthy controls. It points to the need to carefully control the samples when testing the microclot hypothesis. NSAIDS, reduced exercise, later blood collection time and dehydration may increase platelet concentration in a sample (and perhaps platelet fragments that might form a core for microclots to aggregate around in further processed samples). Gender and age are also mentioned as factors that can influence sample composition.