Aplastic Crisis
A sudden, temporary halt in red blood cell production
Quick Facts
- Type: Blood and bone marrow emergency
- Common trigger: Parvovirus B19 infection
- Highest risk: People with chronic hemolytic anemias
- Action: Sudden severe anemia needs urgent care
Overview
An aplastic crisis is a sudden, temporary stop in the bone marrow's production of new red blood cells. Normally the marrow constantly replaces old red cells as they are removed. When this production pauses, the red cell count can fall quickly, leading to severe anemia over a matter of days.
The most common trigger is infection with parvovirus B19, the virus that causes a common childhood rash illness. The crisis is especially dangerous for people who already have a condition in which red cells break down or are lost faster than normal, such as sickle cell disease or hereditary spherocytosis, because they depend on rapid red cell production to keep their counts up.
Symptoms
Symptoms reflect a rapidly falling red blood cell count and the body's struggle to deliver enough oxygen:
- Extreme tiredness and weakness
- Pale skin
- Shortness of breath, especially with activity
- Rapid or pounding heartbeat
- Dizziness or fainting
- Headache
- In children, unusual sleepiness or irritability
Because the drop in red cells can happen quickly, symptoms may worsen rapidly. There may also be signs of the triggering viral infection, such as a mild fever or rash.
Causes
An aplastic crisis happens when the bone marrow briefly stops making red blood cells. The leading cause is infection with parvovirus B19, which temporarily infects and shuts down the cells that produce red blood cells.
In healthy people, this brief pause causes little trouble because the body has a reserve of red cells. But in people with chronic conditions that shorten red cell survival, such as sickle cell disease, thalassemia, hereditary spherocytosis, or other hemolytic anemias, even a short pause can cause a sharp and dangerous fall in red cell count. Other infections and some medications can occasionally contribute. The reason is simple: people with these disorders already remove red cells far faster than usual and rely on the bone marrow constantly producing new ones. When that production stops, even briefly, there is no reserve to fall back on, so the count drops quickly.
Risk Factors
- Sickle cell disease or other sickling disorders
- Hereditary spherocytosis or elliptocytosis
- Thalassemia and other chronic hemolytic anemias
- Recent parvovirus B19 infection
- Close contact with infected children, where the virus spreads easily
Diagnosis
Diagnosis focuses on confirming the sudden drop in red cells and identifying the cause.
- Complete blood count: shows a low red blood cell count and hemoglobin
- Reticulocyte count: a very low count of young red cells signals that the marrow has stopped producing them, a key feature of aplastic crisis
- Viral testing: tests for parvovirus B19 to identify the trigger
- Review of underlying condition: assessing any known hemolytic anemia
Treatment
An aplastic crisis is usually temporary, and the goal is to support the person until the marrow recovers, typically within a couple of weeks.
- Blood transfusion: the main treatment for severe anemia, to restore red blood cells while the marrow recovers
- Close monitoring: frequent blood counts to track recovery and the need for transfusion
- Supportive care: rest and management of the triggering infection
- Treating the underlying condition: ongoing care for the person's chronic blood disorder
Most people recover well once the bone marrow resumes making red cells. After a parvovirus B19 infection, people usually develop immunity that prevents future crises from the same virus.
Prevention
- People with chronic hemolytic anemias should be aware of the risk and seek care quickly if symptoms develop
- Practice good hand hygiene to reduce the spread of viral infections
- Limit close contact with people who have a known parvovirus infection when possible
- Keep up with regular care for any underlying blood disorder
When to See a Doctor
Seek urgent medical care if you or your child, especially with a known blood disorder, develop signs of sudden severe anemia:
- Rapidly worsening tiredness, weakness, or pale skin
- Shortness of breath or a racing heartbeat
- Dizziness or fainting
- Unusual drowsiness or irritability in a child
People with sickle cell disease or other hemolytic anemias should treat these signs as an emergency, because the red cell count can fall quickly and may require a transfusion.
Frequently Asked Questions
What causes an aplastic crisis?
It is most often triggered by infection with parvovirus B19, which temporarily shuts down the cells in the bone marrow that make red blood cells. In people whose red cells already break down quickly, even this brief pause causes a sharp drop in red cell count.
Who is most at risk of an aplastic crisis?
People with chronic conditions that shorten red cell survival are at greatest risk, including those with sickle cell disease, thalassemia, hereditary spherocytosis, and other hemolytic anemias. Healthy people rarely have serious problems from the same trigger.
Is an aplastic crisis an emergency?
It can be. Because the red cell count can fall quickly, severe anemia may develop within days. People with a known blood disorder who become very tired, pale, breathless, or dizzy should seek urgent care, as a transfusion may be needed.
How is an aplastic crisis treated?
The main treatment is a blood transfusion to restore red cells while the bone marrow recovers, along with close monitoring and management of the triggering infection. The marrow usually resumes production within about two weeks.
Can it happen more than once?
An aplastic crisis from parvovirus B19 usually happens only once, because people typically develop lasting immunity to the virus afterward. However, the underlying blood disorder still needs ongoing care.
References
- MedlinePlus, U.S. National Library of Medicine. Aplastic anemia and red cell aplasia.
- National Heart, Lung, and Blood Institute (NHLBI).
- Centers for Disease Control and Prevention (CDC). Parvovirus B19 and Fifth Disease.
- American Society of Hematology.