Serum Sickness

What is SERUM?

Serum: The clear liquid that can be separated from clotted blood. Serum differs from plasma, the liquid portion of normal unclotted blood containing the red and white cells and platelets. It is the clot that makes the difference between serum and plasma.

"Serum" is a Latin word that refers to the "whey", the watery liquid that separates from the curds in the process of cheesemaking.

The term "serum" also is used to designate any normal or pathological fluid that resembles serum as, for example, the fluid in a blister.

Serum Sickness

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

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 (such as penicillin, cefaclor, and sulfa) 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 develops 7 - 21 days after the first exposure to a medication.

Injected proteins such as antithymocyte globulin (used to treat transplant rejection) and rituximab (used to treat immune disorders and cancers) cause serum sickness reactions.

Blood products may also cause serum sickness.

The usual symptoms are severe skin reactions, often on the palms of the hands and soles of the feet. Fever, sometimes as high as 104o F, is always present and usually appears before the skin rash.

Swelling of lymph nodes, particularly around the site of the injection, is seen in 10-20% of cases. There may also be swelling of the head and neck.

Other symptoms may involve the heart and central nervous system. These may include changes in vision, and difficulty in movement. Breathing difficulty may occur.

Treatment

The first step in treatment of serum sickness is always to discontinue the drug or other substance which is suspected of causing the reaction. After that, all treatment is symptomatic. Antihistamines, pain relievers, and corticosteroids may be given to relieve the symptoms. The choice of treatment depends on the severity of the reaction.

Prevention

The most effective method of prevention is simple avoidance of antitoxins that may cause serum sickness. If patients have had a reaction in the past, particularly if the reaction was to a commonly used drug, they should be made aware of it, and be advised to alert physicians and hospitals in the future. Patients who have had particularly severe reactions may be advised to wear identification bracelets, or use other means to alert health care providers.