What Causes Low Hemoglobin Levels?

“Blood pigment” is a colloquial term now uniformly referred to as hemoglobin—a key indicator used to assess whether a patient has anemia. Anemia is defined as a reduction in hemoglobin concentration below the reference range, resulting from blood loss or decreased production due to various causes. So, what are the underlying reasons for low hemoglobin levels? Below, we address this question.

Causes of Low Hemoglobin Levels

1. Physiological Factors

With advancing age, rapid growth and development may lead to relative insufficiency of hematopoiesis (blood cell production) by the bone marrow—typically resulting in hemoglobin levels 10–20% lower than normal. During the second and third trimesters of pregnancy, increased plasma volume dilutes the blood, thereby lowering hemoglobin concentration. In elderly individuals, declining bone marrow function can also reduce red blood cell and hemoglobin production. Additionally, major trauma often results in significant hemorrhage; substantial blood loss directly decreases hemoglobin quantity, leading to low hemoglobin levels.

2. Pathological Factors

These include bone marrow failure syndromes such as aplastic anemia and myelofibrosis-associated anemia. Furthermore, hepatitis B virus (HBV) infection can suppress bone marrow hematopoietic function, impairing red blood cell maturation and consequently reducing hemoglobin synthesis. Under HBV influence, patients may also develop hepatitis, hypersplenism, and splenomegaly—all of which can cause varying degrees of damage to red blood cells. Similarly, severe postoperative or postpartum hemorrhage significantly depletes hemoglobin levels.

3. Anemia-Related Causes

A low mean corpuscular hemoglobin concentration (MCHC) suggests the presence of anemia. Common anemias include megaloblastic anemia, iron-deficiency anemia, sideroblastic anemia, aplastic anemia, hemolytic anemia, and thalassemia. Any of these conditions may lead to decreased hemoglobin levels. Therefore, timely intervention and management are essential to prevent complications associated with chronic anemia and to safeguard overall health.

The above outlines the primary causes of low hemoglobin levels. We hope this information is helpful to you.