Serum sickness is a hypersensitivity reaction similar to an allergy. Specifically, it is an immune system reaction to certain medications or antiserum, the liquid part of blood that contains antibodies that help protect against infectious or poisonous substances.

See also:Immune response

Serum is the clear fluid portion of blood. It does not contain blood cells, but it does contain many proteins, including antibodies, which are formed as part of the immune response to protect against infection.

Antiserum is taken from a person or animal with immunity against a particular infection or poisonous substance. Antiserum may be used when a person has been exposed to a potentially dangerous microorganism against which the person has not been immunized. For example, you may receive a certain type of antiserum injection if you have been exposed to tetanus and rabies. This is called passive immunization. It gives you immediate, but temporary, protection while your body develops a personal immune response against the toxin or microorganism.

During serum sickness, the immune system misidentifies a protein in antiserum as a potentially harmful substance (antigen). The result is a faulty immune system response that attacks the antiserum, causing inflammation and other symptoms.

Certain medications (particularly penicillin) can cause a similar reaction. Unlike other drug allergies, which occur very soon after receiving the medication for the second (or subsequent) time, serum sickness can develop 7 - 21 days after the first exposure to a medication.

Blood products may also cause serum sickness.

• Fever
• General ill feeling
• Hives
• Itching
• Joint pain
• Rash
• Swollen lymph nodes

Note: Symptoms usually do not develop until 7 - 21 days after the first dose of antiserum. However, some people may develop symptoms in 1 - 3 days if they have previously been exposed to the substance.

The lymph nodes may be enlarged and tender to the touch. The urine may contain blood or protein. Blood tests may show signs of blood vessel inflammation.