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Hemolysis. Red blood cells with (right) and without (left and middle) hemolysis.

Hemolysis (or haemolysis)—from the Latin Hemo-, Greek Αἷμα meaning blood, -lysis, meaning to break open—is the breaking open of red blood cells and the release of hemoglobin into the surrounding fluid (plasma, in vivo).

Main article: Hemolytic anemia

In vivo hemolysis, which can be caused by a large number of conditions, can lead to anemia.

Anemias caused by in vivo hemolysis are collectively called hemolytic anemias.

In vitro hemolysis can be an important unwanted effect in medical tests and can cause inaccurate results, because the contents of hemolysed red blood cells are included with the serum. The concentration of potassium inside red blood cells is much higher than in the serum and so an elevated potassium is usually found in biochemistry tests of hemolysed blood. If as little as 0.5% of the red blood cells are lysed the serum will have a visually obvious pinkish colour, due to hemoglobin.

In vitro hemolysis can occur in a blood sample owing prolonged storage or storage in incorrect conditions (ie too hot, too cold). Hemolysis can also occur at the time of venipuncture, but it is uncommon when the venipuncture is straightforward and the phlebotomist is experienced. Excessive suction can cause the red blood cells to be literally smashed on their way through the hypodermic needle owing to turbulence and physical forces. Such hemolysis is more likely to occur when a patient's veins are difficult to find or when they collapse when blood is removed by a syringe or a modern vacuum tube.

In some surgical procedures (esp. some heart operations) where substantial blood loss is expected, machinery is used for intra-operative blood salvage. A centrifuge process takes blood from the patient, washes the red blood cells with normal saline, and returns them to the patient's blood circulation. Hemolysis may occur if the centrifuge rotates too quickly (generally greater than 500 rpm)—essentially this is hemolysis occurring outside of the body. Unfortunately, increased hemolysis occurs with massive amounts of sudden blood loss, because the process of returning patient's cells must be done at a correspondingly higher speed to prevent hypotension, pH imbalance, and a number of other hemodynamic & blood level factors.

Hemolyses of streptococci. (from left) Alpha, beta and gamma.

Main article: Hemolysis (microbiology)

Hemolytic patterns of the various Gram positive cocci; Streptococci are differentiated by hemolysis of red blood cells on blood agar (BA) plates.

• Alpha hemolysis is shown by a greenish halo around the colony and is the result of hemoglobin reduction to methaemoglobin in red blood cells.
• Beta hemolysis is shown by a clear halo around the colony and is produced by complete hemolysis of the red blood cells.
• Gamma hemolysis is shown as no hemolysis or discoloration of the blood.

• Hemolysin

• Effects of Hemolysis on Clinical Specimens