Hemolysis (or haemolysis)—from the Latin Hemo-, Greek 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).

In vivo hemolysis

In vivo hemolysis can be caused by one of a large number of conditions. Anemias caused by in vivo hemolysis are collectively called hemolytic anemias.

In vitro hemolysis

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. 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.

Hemolysis due to mechanical blood processing during surgery

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 RBC's 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 rpms) — 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.

Hemolysis in 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 produced by partial hemolysis of the 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.

While a blood agar plate may contain varying concentrations of RBCs and may use blood from a variety of animals, clinical results are most often reported on 5-10% sheep blood agar plates (SBAP).

Types of hemolysis

• Alpha hemolysis (?-hemolysis) is present if there is a greenish darkening of the agar under the colonies. Streptococcus pneumoniae displays alpha hemolysis. This is sometimes called green hemolysis because of the color change in the agar. Other synonymous terms are incomplete hemolysis and partial hemolysis. Alpha hemolysis is generally caused by peroxides produced by the bacteria.

• Beta hemolysis (?-hemolysis) is caused by a complete lysis of the red cells in the media. The area around and under the colonies are lightened and transparent. Streptococcus pyogenes, or Group A beta-hemolytic Strep, displays beta hemolysis. Beta hemolysis is sometimes called complete hemolysis. Beta hemolysis is caused by hemolysins.
  • Some weakly beta hemolytic species will cause intense beta hemolysis when grown together with a strain of Staphylococcus. This is called the CAMP test¹. Streptococcus agalactiae displays this property. Clostridium perfringens can be identified presumptively with this test.

• If an organism does not cause hemolysis, it is said to display gamma hemolysis (?-hemolysis): the agar under and around the colony is unchanged (this is also called non-hemolytic). Enterococcus faecalis (formerly called Group D Strep) displays gamma hemolysis.

Notes

¹The CAMP test is so called from the initials of those who initially described it, R. Christie, N. E. Atkins, and E. Munch-Peterson.

References

• Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill. ISBN 0-8385-8529-9.

External links

• Effects of Hemolysis on Clinical Specimens