Lysis of Red Blood Cells: Causes and Consequences

The lysis of red blood cells, medically termed hemolysis, is the destruction of these cells. Red blood cells transport oxygen from the lungs to every tissue in the body and return carbon dioxide to be exhaled. Their integrity is fundamental to this process. When these cells are destroyed prematurely, this oxygen delivery service is disrupted. This article explores the processes, causes, and consequences of excessive red blood cell lysis.

The Process of Hemolysis

The destruction of a red blood cell, or erythrocyte, occurs when its outer membrane is breached, releasing its contents, primarily hemoglobin. This process can occur within blood vessels (intravascular hemolysis) or outside of the bloodstream in the spleen and liver (extravascular hemolysis). In intravascular hemolysis, the cell breaks apart directly in circulation, releasing hemoglobin into the plasma.

One mechanism is osmotic lysis, which happens when the fluid outside the red blood cell is more dilute than the fluid inside. This imbalance forces water into the cell, causing it to swell and burst like an overfilled water balloon.

Physical force can also cause mechanical lysis by tearing the cell membrane apart. For example, turbulent blood flow from artificial heart valves or obstructed blood vessels can create enough shear stress to rip the cells apart. Lastly, chemical agents and toxins can induce lysis by directly attacking the cell membrane, such as certain snake venoms and bacterial toxins that punch holes in it.

Causes of Excessive Hemolysis

The body naturally recycles old red blood cells after their 120-day lifespan, but excessive hemolysis is a condition where destruction outpaces production. These causes are categorized as either intrinsic, originating from a defect within the red blood cell, or extrinsic, where an external factor attacks a healthy cell.

Intrinsic causes are often inherited conditions affecting the structure or function of red blood cells. In sickle cell disease, abnormal hemoglobin causes cells to become rigid and crescent-shaped, leading to premature destruction. Thalassemia involves impaired hemoglobin production, while hereditary spherocytosis results from membrane protein defects, making cells abnormally spherical and fragile.

Extrinsic causes involve external factors that destroy healthy red blood cells. In autoimmune hemolytic anemia, the immune system mistakenly produces antibodies that mark red blood cells for destruction. Infections like malaria involve parasites that rupture red blood cells as part of their life cycle. Other extrinsic causes include toxins like lead, mechanical damage from devices like heart-lung bypass machines, and adverse reactions to certain medications, including penicillin.

Medical Consequences and Symptoms

The premature destruction of red blood cells has significant effects, stemming from both the loss of oxygen-carrying capacity and the release of hemoglobin into the bloodstream. These impacts can develop slowly or appear suddenly, depending on the cause.

The most direct outcome is hemolytic anemia, a condition where the rate of red blood cell destruction exceeds the bone marrow’s ability to produce replacements. This deficit in functioning red blood cells impairs oxygen delivery to tissues, causing symptoms such as:

• Fatigue and weakness
• Dizziness
• Pale skin (pallor)
• Shortness of breath

When red blood cells rupture, they release hemoglobin, which is broken down into a yellow pigment called bilirubin. If hemolysis is excessive, the liver cannot process the bilirubin fast enough, leading to its accumulation and causing jaundice—a yellowing of the skin and eyes. The large quantity of free hemoglobin can also be harmful to the kidneys and cause urine to turn a dark, reddish-brown color (hemoglobinuria). An enlarged spleen may also occur as it works to clear damaged cells from circulation.

Diagnosis and Medical Evaluation

Healthcare professionals diagnose excessive hemolysis through laboratory tests designed to confirm the destruction of red blood cells and identify the cause. The initial evaluation starts with a complete blood count (CBC). This test measures the number of red blood cells, hemoglobin, and hematocrit, which are low in cases of hemolytic anemia.

A reticulocyte count is performed to see if the bone marrow is compensating for the cell loss. Reticulocytes are immature red blood cells, and an elevated count indicates the bone marrow has increased production. A peripheral blood smear is also examined under a microscope to inspect the size and shape of red blood cells, which can reveal abnormalities characteristic of conditions like sickle cell disease.

Further blood tests measure specific markers of hemolysis. These include tests for increased levels of lactate dehydrogenase (LDH) and bilirubin, which are substances released from destroyed red blood cells. Levels of a protein called haptoglobin are also measured. Haptoglobin binds to free hemoglobin, so low levels suggest it is being used up to clear excess hemoglobin from the blood, which points toward intravascular hemolysis.