FAQ ON MEAN CORPUSCULAR HAEMOGLOBIN (MCH) AND ITS CLINICAL SIGNIFICANCE
WHAT IS MEAN CORPUSCULAR HAEMOGLOBIN (MCH), AND WHY IS IT IMPORTANT IN A FULL BLOOD COUNT (FBC)?
Mean Corpuscular Haemoglobin (MCH) is a measure of the average amount of haemoglobin contained in a single red blood cell. Haemoglobin is the protein in red blood cells responsible for carrying oxygen from the lungs to the rest of the body and returning carbon dioxide to the lungs for exhalation. MCH is an important parameter in a Full Blood Count (FBC) because it provides insight into the haemoglobin content of your red blood cells, which is crucial for assessing the blood’s ability to transport oxygen. By evaluating MCH alongside other red blood cell indices, doctors can diagnose different types of anaemia and other blood disorders.
WHAT IS THE NORMAL RANGE FOR MCH IN AN FBC?
The normal range for MCH in adults is typically between 27 and 33 picograms (pg) per cell. This range can vary slightly depending on the laboratory’s reference values and individual factors such as age and overall health. An MCH within the normal range indicates that your red blood cells contain a typical amount of haemoglobin, which is essential for carrying oxygen efficiently throughout the body. However, MCH values outside this range can suggest various forms of anaemia or other conditions affecting red blood cells.
WHAT DOES A LOW MCH (HYPOCHROMIC ANAEMIA) INDICATE?
A low MCH, often referred to as hypochromia, means that your red blood cells contain less haemoglobin than normal. This condition is usually associated with hypochromic anaemia, where the red blood cells are paler in colour due to the reduced haemoglobin content. The most common cause of low MCH is iron-deficiency anaemia, which occurs when there is not enough iron available to produce adequate haemoglobin. This type of anaemia is frequently seen in individuals with chronic blood loss, such as from gastrointestinal bleeding or heavy menstrual periods, as well as in those with poor dietary iron intake.
Other causes of low MCH include thalassaemia, a genetic disorder that affects haemoglobin production, and certain chronic diseases that interfere with iron metabolism, such as chronic kidney disease or inflammatory conditions. Symptoms of hypochromic anaemia can include fatigue, weakness, shortness of breath, and pallor, all related to the reduced oxygen-carrying capacity of the blood due to lower haemoglobin levels in each red blood cell.
WHAT DOES A HIGH MCH (HYPERCHROMIC ANAEMIA) INDICATE?
A high MCH, known as hyperchromia, means that your red blood cells contain more haemoglobin than normal. This condition is often associated with macrocytic anaemia, where the red blood cells are larger and have a higher haemoglobin content. One of the most common causes of high MCH is vitamin B12 or folate deficiency, both of which are necessary for proper DNA synthesis during red blood cell production. This deficiency leads to the production of fewer, but larger, red blood cells that contain more haemoglobin.
Other causes of high MCH include certain medical conditions, such as liver disease, and the use of specific medications, such as chemotherapy drugs. In some cases, a high MCH may be seen in patients with autoimmune haemolytic anaemia, where the body’s immune system mistakenly attacks and destroys red blood cells, leading to a compensatory increase in the production of larger red blood cells with higher haemoglobin content. Symptoms of hyperchromic anaemia are similar to those of other types of anaemia and can include fatigue, weakness, and difficulty concentrating. In some cases, the underlying vitamin B12 deficiency can also cause neurological symptoms, such as numbness, tingling, and memory problems.
HOW DOES MCH RELATE TO OTHER FBC PARAMETERS?
MCH is closely related to other parameters in the Full Blood Count (FBC), such as Mean Corpuscular Volume (MCV), Mean Corpuscular Haemoglobin Concentration (MCHC), and Haemoglobin levels. MCV measures the average size of your red blood cells, while MCHC indicates the concentration of haemoglobin within a given volume of red blood cells. These indices are often used together to diagnose and differentiate between different types of anaemia.
For example, in microcytic anaemia (characterised by small red blood cells), both MCH and MCV are typically low, indicating that the red blood cells are smaller and contain less haemoglobin. This pattern is commonly seen in iron-deficiency anaemia and thalassaemia. In contrast, macrocytic anaemia (characterised by large red blood cells) often presents with high MCH and MCV, as seen in vitamin B12 or folate deficiency. In normocytic anaemia, where red blood cells are of normal size but fewer in number, MCH might be within the normal range, but overall haemoglobin levels are reduced.
MCHC is another important related parameter that measures the average concentration of haemoglobin in your red blood cells. A low MCHC, combined with low MCH, often points to hypochromic microcytic anaemia, where the red blood cells are both smaller and paler due to reduced haemoglobin. Conversely, a high MCHC can occur in conditions like hereditary spherocytosis, where red blood cells are more spherical and have a higher haemoglobin concentration.
WHAT IS THE SIGNIFICANCE OF MCH IN CLINICAL PRACTICE?
MCH is a critical tool in diagnosing and managing anaemia and other blood disorders. By evaluating MCH alongside other red blood cell indices, doctors can determine the type of anaemia a patient has and identify its underlying cause. For example, if MCH is low, doctors may investigate iron levels and assess for signs of chronic blood loss or malabsorption. If MCH is high, they may test for vitamin B12 and folate deficiencies or consider liver function tests and the patient’s medication history.
MCH is also valuable in monitoring the effectiveness of treatment. In patients receiving iron supplements for iron-deficiency anaemia, MCH should gradually return to normal as iron levels are restored and red blood cells of normal haemoglobin content are produced. Similarly, in patients treated for vitamin B12 or folate deficiency, MCH should decrease as the underlying deficiency is corrected, reflecting the production of normal-sized red blood cells with appropriate haemoglobin content.
In some cases, MCH can provide early clues to underlying health issues before more significant symptoms develop. For instance, a mild increase in MCH might be an early sign of vitamin B12 deficiency, prompting further investigation and early intervention before neurological symptoms arise.
CAN MCH LEVELS FLUCTUATE, AND WHAT FACTORS INFLUENCE THESE FLUCTUATIONS?
Yes, MCH levels can fluctuate due to various factors, including changes in health, medications, and lifestyle. Acute illnesses or infections can temporarily affect MCH, as the body’s red blood cell production may be altered in response to stress or inflammation. Dehydration can also influence MCH, as it may cause red blood cells to appear more concentrated due to reduced plasma volume.
Medications, particularly those that affect red blood cell production or DNA synthesis, can also impact MCH. For example, certain chemotherapy drugs may increase MCH by disrupting normal red blood cell production, leading to the creation of larger cells with more haemoglobin. On the other hand, long-term iron deficiency or chronic blood loss may gradually lower MCH as the body’s haemoglobin stores become depleted.
In some cases, MCH may fluctuate as a response to treatment. For example, in patients being treated for anaemia, MCH may initially change as the bone marrow responds to therapy and begins producing red blood cells of different haemoglobin content. Over time, with effective treatment, MCH should stabilise within the normal range.
WHAT DO DOCTORS CONSIDER WHEN INTERPRETING MCH LEVELS IN PATIENTS WITH OTHER HEALTH CONDITIONS?
When interpreting MCH levels, doctors must consider the patient’s overall health, underlying conditions, medications, and other FBC parameters. For instance, in a patient with chronic kidney disease, a low MCH might suggest iron-deficiency anaemia, which is common in this population due to reduced iron absorption and increased blood loss. In such cases, treatment might involve iron supplements or erythropoiesis-stimulating agents to increase red blood cell production.
In patients with known vitamin B12 or folate deficiency, a high MCH is expected, and treatment should focus on correcting the deficiency through dietary changes, supplements, or injections. If MCH remains elevated despite treatment, doctors may need to investigate other potential causes, such as liver disease or medication side effects.
Doctors should also consider whether MCH is consistent with other FBC findings. For example, if MCH is low but MCV is normal, it might suggest an early stage of iron-deficiency anaemia, before the red blood cells have become noticeably smaller. Conversely, if MCH is high but MCV is low, it could indicate a mixed anaemia, where some red blood cells are larger and contain more haemoglobin, while others are smaller and contain less. In such cases, a comprehensive approach to diagnosis and treatment is needed to address all underlying causes.
Overall, interpreting MCH requires a holistic view of the patient’s health, including a careful analysis of symptoms, medical history, and other laboratory results.
