Soluble serum transferrin receptor increases acutely after exercise but is not an " acute phase reactant" ?

 At least two research projects in runners and rowers have demonstrated elevation of the soluble serum transferrin receptor after strenuous exercise. and in one of the articles the soluble receptor had returned to normal in 24 hours.

The point to be made is that both reticulocyte hemoglobin content and the soluble serum transferrin receptor are generally said to not be acute phase reactants but technically that is not correct in regard to the Soluble serum transferrin receptor .It does rise acutely but would likely be back to baseline by the time an athlete would be evaluated for anemia. So for almost all practical situations it is not   an  acute phase reactant as the value is likely to be back to baseline by 24 hours.Of course if an endurance athlete does their early morning work out and then goes to lab  that day for a blood draw the serum transferrin receptor level could be elevated misleading the doctor into thinking the test indicated iron deficiency anemia.

So both iron deficiency and acute strenuous exercise can elevate the serum transferrin receptor.With the significant perturbations in certain measures of body iron caused by strenuous exercise two tests have become the go-to tests to differentiate iron deficiency anemia from anemia of inflammation: the reticulocyte hemoglobin concentration and the soluble serum transferrin receptor.The National Kidney Foundation recommends the reticulocyte hemoglobin as the preferred test to detect iron deficiency in renal failure patients.  

1.Auersperger,L The effect of eight weeks of strenuous exercise

2.Skarpansa-Stejnborn A Effect of intense physical exercise on hepcidin  

Addendum:   7/22/22

A 2010 article provides contradictory data. Sim et al (senior author is Peter Peeling) 

In subjects who exercised at 75% of 02 max for 90 minutes were shown to have a decreased soluble serum transferrin receptor at 3 hrs and again at 24 hours. ( The effects of carbohydrate ingestion during endurance running on post exercise inflammation and hepcidin levels. Eur J app Physio nov 2010.