Karl Landsteiner

Unraveling the Mysteries of Blood

There was a time when today’s medical procedures were so dangerous that they were banned in some places. That includes both surgery and blood transfusion, each of which used to kill roughly half of all patients through infection and immune rejection of transfused blood.

Thankfully, the work of two brilliant medical minds—Joseph Lister and Karl Landsteiner—helped pave the way for modern medicine as we know it. Lister’s groundbreaking research on antiseptics dramatically reduced the incidence of infection in surgery (we have covered this story in a previous episode), while Landsteiner’s discovery of different blood groups (such as A, B, and O) made it possible to safely transfuse blood without rejection. With this knowledge, medical professionals could select the right blood type for a patient and prevent immune rejection, revolutionizing the practice of blood transfusion. It couldn’t have come at a more critical time—Europe was embroiled in World War I, and the need for transfusions was at an all-time high.

Karl Landsteiner in his laboratory at the Rockefeller Institute for Medical Research (Rockefeller University). New York, 1930.

Born in Vienna in 1868, Landsteiner had a keen interest in biochemistry from a young age. By the time he was a medical student, he was already publishing research in the field. But it was immunology that truly captivated Landsteiner, and he pursued his interest in the nature of antibodies with unrelenting passion.

In the annals of medical history, the practice of blood transfusions has been fraught with danger and controversy. In England, animal-to-human transfusions were banned as far back as 1670 due to the high number of adverse—and often fatal—reactions they caused. In the 19th century, doctors resumed their experiments with human-to-human transfusions, but the results were similarly disastrous, leading to widespread condemnation of the practice.

Despite these setbacks, medical researchers persevered in their quest for a safer way to perform transfusions. Although they knew that foreign blood cells tended to clump together in the bloodstream of recipients, they lacked a clear understanding of why this occurred. Landsteiner was among the first to point out that the reaction was similar whether animal-to-human or human-to-human; this may not have been obvious because the process was too dangerous for large-scale testing.

Google Doodle on June 14, 2016, to honor Karl Landsteiner on his 148th birthday

Landsteiner’s pioneering work on blood typing began with his experiments on the blood of his laboratory workers. He mixed serum from one individual with the red cells of others and observed the reactions. To his surprise, he observed either strong agglutination or no reaction at all instead of the weak or negative reactions that he had anticipated. These findings led him to classify blood into three groups: A, B, and C (later renamed O for “Ohne,” meaning “without” in German or “zero/null” in English). A year later, he discovered the fourth, less common blood group, AB.

He showed that transfusions between individuals within the same blood group do not result in the destruction of new blood cells, which otherwise would cause severe reactions in people receiving the wrong blood type. As you may know, people with AB can safely receive A or B blood, and anyone can accept type O. Interestingly, in 1901, Landsteiner also suggested that his blood group discovery could be helpful in resolving paternity cases, a testament to the far-reaching implications of his research.

Although Landsteiner began communicating these realizations around 1900, they were not widely acknowledged until 1909, two years after the first successful transfusion was performed at Mount Sinai Hospital in New York.

Austrian postage stamp honoring Karl Landsteiner, issued on the 100th anniversary of his birth, 1968

In the aftermath of World War I, Europe’s economy was in a dire state, prompting Karl Landsteiner to seek new opportunities elsewhere. In 1923, he moved to New York and joined the Rockefeller Institute, where he focused on investigating problems related to immunity and allergy. Four years later, he made a groundbreaking discovery of new blood groups—M, N, and P—and published his findings. Shortly after, Landsteiner witnessed the application of his blood groups in paternity suits, just as he had suggested 25 years earlier.

In recognition of his significant contributions to medicine, Landsteiner was awarded the Nobel Prize in Physiology/Medicine in 1930. He continued to work for the Rockefeller Institute on immunology and blood groups until June 1943, when he tragically passed away from a heart attack while working in his laboratory. Landsteiner’s contributions to medicine, particularly his pioneering work on blood groups, have had a profound impact on the field and saved countless lives.


“I told the ambulance men the wrong blood type for my ex, so he knows what rejection feels like.” —Pippa Evans

“What is happening to me happens to all fruits that grow ripe. It is the honey in my veins that makes my blood thicker, and my soul quieter.” —Friedrich Nietzsche

“The art of medicine consists of amusing the patient while nature cures the disease.” —Voltaire

“Always laugh when you can, it is cheap medicine.” —Lord Byron


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