anemia

anemia. A condition characterized by a deficiency in the number or quality of red blood cells or the hemoglobin they contain, impairing the blood's oxygen-carrying capacity. It is a common disorder with a wide array of etiologies, ranging from nutritional deficiencies to chronic diseases and genetic abnormalities. The clinical presentation can vary from asymptomatic to severe fatigue, and its management is directed at correcting the underlying cause.

Definition and classification

The World Health Organization defines the condition based on specific hemoglobin thresholds, which vary by factors such as age and sex. It is broadly classified by the size of the red blood cells, measured as mean corpuscular volume, into microcytic, normocytic, and macrocytic types. Other classification systems consider the underlying mechanism, such as decreased production seen in iron deficiency or increased destruction as in hemolytic anemia. The morphological approach, focusing on erythrocyte indices, is fundamental for guiding initial diagnostic evaluation in clinical practice.

Causes and pathophysiology

Etiologies are diverse and often specific to the morphological classification. Microcytic forms frequently result from iron deficiency, thalassemia, or sideroblastic anemia, often involving disruptions in heme or globin synthesis. Normocytic anemia can stem from acute blood loss, chronic diseases like rheumatoid arthritis or chronic kidney disease, or bone marrow disorders such as aplastic anemia. Macrocytic types are commonly associated with deficiencies in vitamin B12 or folic acid, or with the use of certain medications like hydroxyurea. Inherited conditions like sickle cell disease and enzymopathies such as glucose-6-phosphate dehydrogenase deficiency cause hemolytic variants through intrinsic red cell abnormalities.

Signs and symptoms

Common manifestations are related to hypoxia and compensatory mechanisms, including fatigue, weakness, dyspnea, and palpitations. Physical signs may encompass pallor of the conjunctiva and nail beds, tachycardia, and a flow murmur detectable on auscultation. More specific findings can point to particular etiologies, such as koilonychia in severe iron deficiency, jaundice in hemolytic anemia, or neurological symptoms like paresthesia in vitamin B12 deficiency. The severity of symptoms often correlates with the acuity of onset and the individual's cardiopulmonary reserve.

Diagnosis

Diagnosis begins with a complete blood count, which assesses hemoglobin, hematocrit, and red cell indices. Examination of a peripheral blood smear by a pathologist can reveal specific morphological clues, such as microcytosis, hypochromia, spherocytes, or sickle cells. Further testing is guided by initial findings and may include serum ferritin, vitamin B12, folate levels, reticulocyte count, and tests for hemolysis like lactate dehydrogenase and haptoglobin. In complex cases, evaluation may involve bone marrow biopsy, hemoglobin electrophoresis, or genetic testing for conditions like hereditary spherocytosis.

Treatment and management

Management is entirely directed at the underlying cause. For iron deficiency, oral ferrous sulfate is standard, though intravenous formulations like iron sucrose may be used in certain cases. Vitamin B12 deficiency is treated with cyanocobalamin injections or high-dose oral supplements. In chronic kidney disease, agents like erythropoiesis-stimulating agents are utilized. Severe cases, particularly from aplastic anemia or myelodysplastic syndrome, may require blood transfusion or definitive therapy with bone marrow transplantation. Surgical intervention may be necessary for anemia caused by gastrointestinal bleeding from sources like colorectal cancer.

Epidemiology

It is a global public health issue, affecting an estimated third of the world's population according to the World Health Organization. Prevalence is highest among young children, pregnant women, and the elderly. Iron deficiency anemia is the most common form worldwide, heavily associated with malnutrition and hookworm infection in developing regions. Geographic distribution of genetic forms is uneven; for instance, sickle cell disease is most prevalent in sub-Saharan Africa and among people of African descent, while thalassemia is more common in the Mediterranean Basin, Southeast Asia, and the Indian subcontinent. Socioeconomic factors significantly influence both the incidence and outcomes of the condition. Category:Blood disorders Category:Hematology