Red blood cell distribution width and obstructive sleep apnea

Red blood cell distribution width (RDW) is a blood test that measures the variability of the size of red blood cells, and is usually reported in common blood work to check for anemia. In the October edition of the Journal of Clinical Sleep Medicine is an article about RDW and obstructive sleep apnea (OSA) - researchers theorize that inflammation, low oxygen levels, and/or sleep fragmentation from OSA could increase the RDW. In this study, researchers studied 108 patients with OSA. Results did show a positive correlation between RDW and OSA severity. However, the numbers are hard for me to interpret. They did not include RDW values for patients without OSA. The RDW values for mild, moderate, and severe OSA are as follows: 13.15 +/- 1.7, 13.10 +/- 2.3, and 14.67 +/- 2.5. I'm no hematologist, but those values seem pretty similar, especially the ones for mild and moderate OSA. There is too much overlap in the values for me to understand the clinical significance. The study authors state that the RDW could not be used as a screening tool because it could be affected by various independent variables. They state that the RDW may be used to give earlier appointments to patients with high RDW values so that they may be treated eariler, since their OSA severity may be worse. I'm not so sure and home sleep studies may be a better and more specific screening and / or diagnostic tool.