A Complete Blood Count (CBC) is a routine laboratory test that provides a detailed snapshot of the cells circulating in the bloodstream. The CBC includes two specific measurements that indicate the average size of blood cells: Mean Corpuscular Volume (MCV) and Mean Platelet Volume (MPV). MCV measures the average size of red blood cells (RBCs), which transport oxygen throughout the body. An elevated MCV means these cells are larger than typical. MPV measures the average size of platelets, the tiny cells essential for blood clotting. When both values are elevated, it signals that both red blood cells and platelets are, on average, larger than expected.
Understanding Elevated Mean Corpuscular Volume
An elevated MCV, known as macrocytosis, means that red blood cells are larger than the normal range of 80 to 100 femtoliters (fL). This increased cell size often reflects underlying issues with cell production or maturation within the bone marrow, where blood cells are made. The presence of these larger cells can be a sign of macrocytic anemia, where the enlarged red blood cells may not efficiently transport oxygen.
A common cause of macrocytosis is a deficiency in either Vitamin B12 or folate (Vitamin B9). Both B-vitamins are necessary for proper DNA synthesis. A deficiency impairs cell division, causing red blood cell precursors to grow larger but fail to divide properly, resulting in the release of large, sometimes immature, red blood cells into the circulation.
Macrocytosis is also frequently associated with chronic alcohol use, which can directly suppress bone marrow function and interfere with folate absorption. Liver disease can also cause a high MCV by altering the lipid composition of the red blood cell membrane, changing the cell’s structure and size. Certain medications, such as those used in chemotherapy or for treating HIV, can similarly interfere with cell division and lead to larger red blood cells.
Understanding Elevated Mean Platelet Volume
A high MPV signifies that the average size of your platelets is larger than normal, typically exceeding 12 fL. Platelets are fragments of larger cells produced in the bone marrow. Generally, newly produced platelets are larger and more reactive than older ones.
An elevated MPV often suggests that the bone marrow is rapidly producing and releasing new, larger platelets into the bloodstream, possibly in response to an increased demand or loss. This frequently occurs when there is increased platelet destruction or consumption, prompting the bone marrow to compensate by accelerating production.
This accelerated production can be seen in conditions involving inflammation or infection, where the immune system’s response triggers the release of newer, more reactive platelets. Certain types of anemia, particularly iron-deficiency anemia, may also be associated with a high MPV. In this context, the larger platelets are sometimes viewed as a compensatory mechanism, as these cells are more active in clotting. Less common causes of elevated MPV include myeloproliferative disorders, where the bone marrow produces too many blood cells, including platelets, that are often large and dysfunctional.
Interpreting Results and Follow-Up Testing
An elevated MCV and MPV together do not provide a final diagnosis but serve as important indicators that guide further investigation. These size measurements must be interpreted alongside other values from the CBC, such as the actual counts of red blood cells, platelets, and white blood cells, as well as the patient’s specific symptoms. For example, a high MCV combined with a low red cell count indicates macrocytic anemia, while a high MPV combined with a low platelet count suggests rapid platelet destruction.
The next diagnostic step often involves reviewing a peripheral blood smear, where a medical professional visually inspects the blood cells under a microscope. This visual check confirms the size and shape abnormalities suggested by the MCV and MPV. It can also identify specific features, such as hyper-segmented neutrophils, which are characteristic of Vitamin B12 or folate deficiency.
Based on the pattern of results, targeted follow-up tests are then ordered to pinpoint the underlying cause. These focused tests may include measuring the blood levels of Vitamin B12 and folate, as these deficiencies are common and treatable causes of high MCV. If liver involvement is suspected, liver function tests will be performed, and if inflammation is the likely driver for high MPV, inflammatory markers may be checked. Ultimately, the combined information from the CBC, the cell size indices, and the patient’s overall health profile allows a healthcare provider to establish the correct diagnosis and determine the appropriate treatment plan.