Hemolysis: Physiology, Causes, Diagnosis and Non-Immunological Mechanisms

It is the phenomenon of the disintegration of erythrocytes (red blood cells or red blood cells). The erythrocyte lacks a nucleus and organelles, so it can not be repaired and dies when it “wears out.”

Hemolysis is the alteration of the membranes of erythrocytes, which causes the release of hemoglobin. It is also defined as the necrosis of erythrocytes and occurs at the end of the life of each erythrocyte.


Hemolysis in vivo occurs if the rate of erythrocyte destruction increases, thus decreasing the lifespan of erythrocytes.

The erythrocytes can be lysed within the vasculature (intravascular hemolysis), mainly in the blood vessels and the heart, and are clinically recognized by hemoglobinemia, hemoglobinuria, and decreased concentration of serum haptoglobin.

Erythrocytes can also be destroyed in macrophages (extravascular hemolysis or intracellular hemolysis) of the mononuclear phagocytic system of the spleen, liver, and bone marrow.

Extravascular hemolysis does not cause hemoglobinemia and hemoglobinuria, but it usually causes hemolytic entry (hyperbilirubinemia associated with bilirubinuria).

Causes of abnormally high levels

Hemolysis in vivo is present in conditions called hemolytic anemias. The causes of hemolytic anemia include:


  • Immunity-mediated destruction of erythrocytes: neonatal isoerolysis, incompatible blood transfusion, drugs including penicillin and heparin.
  • Hemoparasites: Babesia spp.
  • Other infectious agents: Leptospira, Ehrlichia, Clostridium, equine infectious anemia virus.
  • Chemical products and plants: red maple, phenothiazine.
  • Fragmentation: disseminated intravascular coagulation (DIC), vasculitis, uremia.
  • Hypo-osmolality: administration of hypotonic fluid.
  • Hipofosfatemia.
  • Hepatic insufficiency: a hemolytic syndrome in horses with liver disease.

The following diagnostic step to consider is if levels are high.

Laboratory artifacts that can interfere with readings of levels of this substance (and how artificially elevated versus depressed)

Mild hemolysis has little effect on most test values; However, when it is moderate to severe, it can interfere directly with the spectrophotometric reading of the absorbance and alter the pH of the reactions.

Aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) has a higher activity within erythrocytes than in plasma, and their levels will increase in hemolysis in vivo or in vitro.

You can falsely increase the following analytes: AST, alanine transaminase (ALT), LDH, total bilirubin, glucose, calcium, phosphorus, complete protein, albumin, magnesium, amylase, lipase, creatine kinase (CK), iron, hemoglobin, and media. The concentration of corpuscular hemoglobin (MCHC).

On the other hand, creatinine, alkaline phosphatase (ALP), potassium, packed cell volume (PCV), and mean corpuscular volume (MCV) can falsely decrease.

Non-immunological mechanisms

Cross-testing blood before transfusion avoided the hemolysis of the transfused red blood cells in the central sequelae. Despite this precaution, blood hemolysis compatible with cross-compatibility is occasionally observed.

In some cases, blood hemolysis compatible with cross-matching is an immune-mediated mechanism involving undetected antibodies. However, there are mechanisms by which the transfused red blood cells can be hemolyzed without an alloantibody.

To begin with, non-immune physical factors can cause hemolysis. For example, erythrocytes are very sensitive to osmotic damage. Therefore, direct lysis may occur if red blood cells are transfused through an intravenous line that simultaneously releases hypotonic saline.

This can lead to massive hemolysis, presenting clinically as an acute hemolytic transfusion reaction. Alternatively, hemolysis of RBC can occur in the recipient due to non-antibody-based factors.

For example, transfusion of donor red blood cells deficient in glucose-6-phosphate dehydrogenase has been reported to cause significant hemolysis, especially in infants. There are also mechanisms dependent on RBC destruction antibodies that do not require antibody binding to RBCs.

For example, activating large-scale complement by immune complexes not associated with red blood cells can lead to the sensitization of the addition of nearby red blood cells, leading to the “spectator hemolysis” of red blood cells not coated with antibodies.

In addition, cellular immunity can lead to hemolysis in rare environments, and it has been reported that natural killer cells can lyse RBCs in negative DHA-AIHA. Despite these non-immunological mechanisms of RBC destruction, care must be taken not to exclude antibody-mediated hemolysis based on a negative antibody screen erroneously.

Although an anti-RBC antibody is usually detectable with immune-mediated destruction of transfused red blood cells, there are exceptions. It has been observed that Rh-positive red blood cells have a reduced lifespan in Rh-negative individuals previously exposed to Rh-positive blood, even if anti-Rh78 antibodies are not detected.

Such individuals usually generate detectable anti-Rh antibodies in subsequent patients—transfusion with Rh-positive blood. Therefore, there appears to be a level of an anti-RBC antibody capable of causing hemolysis but is below the detection threshold by agglutination-based assays.

In addition, not all antibodies that bind to RBCs in vivo are detected in vitro. In addition, anamnestic responses can result in an initial negative scan followed by delayed hemolysis and conversion to a positive scan.