A number of blood abnormalities have been detected in patients who present with ME/CFS, it is hypothesised that these may result in a number of symptoms that are experienced by patients, though taking steps to address various of these abnormalities has resulted in symptomatic relief for a number of patients, a reliable 'cure' has yet to result from blood work.
A high proportion of ME/CFS patients have been shown via a Dual Tag Test to have significantly lower blood volume than healthy controls.  Dr. Nancy Klimas who was a member of the team who showed this has since been quoted as saying by way of a Layman's explanation: “You guys are about a litre short in blood volume, ok? If I’m sitting at five litres, you’re sitting at four. So, you’re really, really sensitive to blood volume changes. If you’re a little dry, you crash. ” 
One study found significantly increased quantities of stomatocytes in the blood of CFS patients. Stomatocytes are red blood cells that have lost their concave shape, usually due to a membrane defect. 
During the early stages of the illness a number of circulating immune markers in the blood have been noted. 
Symptoms Resulting from Abnormalities
The various forms of Orthostatic intolerance that a number of ME/CFS patients suffer have been linked to under-oxygenation of the brain  due to a combination of red blood cell abnormalities and low blood volume. It has also been suggested that blood pressure and other circulatory system abnormalities contribute to this under-oxygenation.  However others state that this may be a direct result of the Adrenal system instead.
Proposed Causes for Blood Abnormalities
Abnormality Treatments and Adjustments
- Wikipedia - Blood
- 2015, Dr. David Bell on Low Blood Volume in Chronic Fatigue Syndrome (see also Doctor David Bell)