Serum sickness is an immune reaction similar to an allergy. The immune system recognizes non-human proteins in certain medications as harmful. Symptoms include fever, rash, itching, and joint pain.

Serum sickness symptoms typically go away on their own a couple of weeks after a person discontinues the exposure to the cause of the reaction.

Non-human proteins are in many treatments, such as antivenom injections, vaccinations, and other treatments for autoimmune conditions. Doctors can prescribe medications to relieve the symptoms.

This article looks at the causes, symptoms, diagnosis, and treatment of serum sickness.

A person with a plaster on their skin after getting a vaccination, some vaccinations cause serum sickness.Share on Pinterest
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Serum sickness is a term used to describe a rare reaction to certain medications containing proteins from other animals (non-human proteins).

It usually occurs in response to antigens made from non-human proteins, which healthcare professionals use to treat immune conditions and protect people against germs and toxins.

When some people have contact with these medications, their immune system reacts in the same way an allergic reaction does. This happens because their body recognizes the non-human proteins as harmful.

Serum sickness is considered a type III hypersensitivity reaction. This is an inappropriate immune response to an antigen that results in unwanted effects.

A person with serum sickness may experience symptoms 1 to 2 weeks after their first exposure to the medication.

The symptoms of serum sickness may include:

Medications that contain non-human antigens are the most common cause of serum sickness.

Serum sickness reaction causes may include:

  • Antivenom injections: One of the most common causes of serum sickness reactions. A review reported that about 5-23% of people getting an antivenom injection due to a venomous snake bite experience serum sickness.
  • Monoclonal antibody therapy: Usually contains rodent antibodies, particularly those from mice. Doctors use it to treat rheumatoid arthritis, psoriasis, and other autoimmune conditions. Some cancer treatments may also contain it.
  • Bee venom injection: This is an alternative treatment for chronic pain and inflammatory conditions.
  • Anti-thymocyte globulin: This usually contains horse or rabbit antibodies. Doctors use this treatment to prevent organ rejection after a kidney transplant.
  • Vaccinations: Some vaccines, such as the one for rabies, may contain non-human proteins that may lead to a reaction.
  • Immune-modulating agents: These are used to treat autoimmune conditions and cancer, and certain types contain animal proteins such as Rituxan (rituximab) and Remicade (infliximab).

To start the diagnosis, the doctor will ask questions about a person’s medical history, the symptoms experienced, when they started, and if they started taking new medications lately.

If a person has a rash, the doctor may collect a skin sample (biopsy) to look at it under a microscope. This procedure may help to rule out other potential causes of the rash. They will then check if the lymph nodes are tender to touch or enlarged.

The doctor may also collect a urine and blood sample, which they will test for any signs of other underlying conditions that may cause similar symptoms. The analysis of urine may also help determine the kidney’s health.

A healthcare professional may suggest discontinuing the medication that caused the serum sickness reaction. This is likely to prevent any further reactions in the future.

Typically, discontinuing the medication that led to the reaction is sufficient; after a couple of weeks, the symptoms should go away on their own.

Other treatments aim to reduce symptoms in people with serum sickness.

Doctors may prescribe a corticosteroid treatment to relieve any discomfort the rash and itching may cause. Antihistamines may also help to improve the rash and shorten the duration of the illness.

Nonsteroidal anti-inflammatory drugs (NSAIDs) may relieve joint pain. These include drugs such as ibuprofen and naproxen.

The doctor may prescribe a 7-10 day course of glucocorticoids for severe reactions to help relieve symptoms.

Doctors classify both serum sickness and Arthus reaction as type III hypersensitivity reactions. However, there are some distinctive differences between these two types of immune reactions.

Here is a comparison between serum sickness and Arthus reaction:

Serum sicknessArthus reaction
Reaction typesystemic localized
Symptomsoccur 7-15 days after exposure to the antigenoccur within 24 hours of exposure to the antigen
Antibodiesthe antibodies causing the reaction form after exposure to the antigen the antibodies causing the reaction are pre-existing

The outlook for serum sickness reactions is usually positive. Symptoms usually resolve within days to weeks after a person stops taking the medication causing serum sickness.

However, people who experience severe symptoms or continuous exposure to the causative agent may take longer to recover.

Typically, serum sickness does not have long-term complications and resolves independently.

However, if a person has repeated exposure to causative agents of serum sickness, they may develop severe complications, such as renal failure. This may also cause death.

Serum sickness may cause severe symptoms. However, it typically goes away on its own within a couple of weeks. In some more severe cases, the recovery may take longer.

If a person has taken a new medication that contains non-human proteins and they experience symptoms of serum sickness, they should contact their doctor as soon as possible.

The doctor will be able to confirm if a person has serum sickness, and they may also prescribe medications to help manage its symptoms.

Here are some answers to frequently asked questions about serum sickness.

Is serum sickness life threatening?

Serum sickness is generally not life threatening, and its symptoms usually resolve independently.

However, repeated exposure to an agent that causes an immune reaction or multiple episodes of serum sickness may lead to kidney failure and death.

What is an example of serum sickness?

The immune reaction may occur in a person because of an injection of antivenom after a venomous snake bite. This is one of the most common cases of serum sickness.

A person may also experience a serum sickness reaction after getting a vaccine or taking a new medication for an autoimmune condition such as arthritis.

Serum sickness is an immune reaction where the immune system identifies non-human proteins as harmful to the body. This can cause a rash, itchy skin, swollen lymph nodes, fever, and more severe symptoms such as kidney failure.

When a serum sickness reaction occurs, it is important to identify the medication causing an immune response so a person can stop taking it.

Doctors can help find out more about the causes of the immune reaction, and they can prescribe medications to control and ease the symptoms.

Symptoms should typically go away a couple of weeks after the person stops taking the medication.