Characteristics of Dilutional Anemia

Anemia caused by enhanced plasma volume is often referred to as dilutional anemia (or hemodilitional anemia). For dilutional anemia the level of red blood cells may be unaffected while the plasma volume is elevated (hypervolemia). This may result in a low hemoglobin concentration and hence indicate anemia while the number of red cells may indeed be normal. Untreated hypervolemic conditions can lead to heart failure and are associated with increase in mortality and readmission rates.

The general medical assumption is that a low hemoglobin concentration is equivalent to a reduced total volume of red blood cells, which, unfortunately, is not always the case since alterations in plasma volume may influence haemoglobin concentration independently of red blood cell volume. A high number of anemic patients are in fact dilutional anemic and these may require different medical treatment than anemic patients, i.e. anemic patients with reduced red blood cell volume.

A recent study demonstrates that red blood cell volume does not correlated well with low hemoglobin concentration in heart failure and cirrhosis patients, suggesting that changes in plasma volume is the main pathology for anemia in these patients. In fact, in 39% of patients the main cause for anemia was an expanded PV.

Research has also demonstrated that among anemic CKD stage 3–5 patients, not on dialysis, that only six patients had a decrease in red blood cell volume as the cause for their anemia, whereas 14 patients had an increase in plasma volume and therefore dilutional anemic.

In another study, eighteen CKD patients undergoing hemodialysis were anemic as determined by hemoglobin concentration. Of these patients, only nine (50%) were anemic related to low  red blood cell volume whereas all patients displayed elevated plasma volume. This study hence confirms the shortcomings of basing anemia diagnosis on the assessment of hemoglobin concentration alone.

The diagnosis of anemia, based on low hemoglobin concentration may be seriously flawed by alterations in plasma volume. This has potential implications for patient treatment as it may be argued that patients with dilutional anemia should be treated for their elevated plasma volume while anemic patients should be treated for their low red blood cell volume. Nonetheless, patients diagnosed with anemia and dilutional anemia are today treated indifferently.