A sickle cell crisis is an episode of sudden, often severe pain that occurs when misshapen red blood cells block small blood vessels and cut off blood flow to nearby tissues. It is the most common reason people with sickle cell disease end up in the hospital, and up to 63% of individuals with the condition experience at least one pain episode per year. Most people with sickle cell disease begin experiencing these crises by age 6.
What Happens Inside Your Body
In sickle cell disease, red blood cells contain an abnormal form of hemoglobin that causes them to stiffen into a crescent or “sickle” shape under certain conditions. These rigid cells stick to white blood cells that are already clinging to the walls of tiny blood vessels called post-capillary venules. As more sickled cells pile up, they create a blockage that chokes off blood flow downstream. The tissues beyond that blockage stop receiving oxygen, which is what produces the intense pain.
This chain reaction also triggers inflammation, which makes the blood vessel walls stickier and attracts even more cells to the area. It becomes a self-reinforcing cycle: the initial blockage worsens inflammation, and the inflammation promotes further blockage.
Types of Sickle Cell Crises
Not every crisis works the same way. The four main types affect the body differently and carry different levels of risk.
Vaso-occlusive crisis is by far the most common. This is the classic pain crisis caused by blocked blood vessels. Pain can strike almost anywhere but most frequently hits the arms, legs, back, and chest. It ranges from moderate to severe, and fever sometimes accompanies it. Episodes typically last days to over a week, depending on severity.
Aplastic crisis occurs when the bone marrow temporarily stops making new red blood cells. The usual culprit is parvovirus B19 (the virus behind “fifth disease” in children), though other infections can trigger it too. Because sickle-shaped red blood cells already have a much shorter lifespan than normal ones, this production halt causes hemoglobin levels to drop rapidly. Symptoms include sudden pallor, weakness, and fatigue. The good news is that the infection is self-limited, typically resolving within 7 to 10 days.
Splenic sequestration crisis happens when sickled cells become trapped inside the spleen, causing it to swell rapidly. This leads to abdominal pain, a visibly distended belly, paleness, and a fast heart rate. In severe cases, so much blood pools in the spleen that blood pressure drops dangerously low, and cardiovascular collapse can follow within hours. This type of crisis is a medical emergency.
Acute chest syndrome is the most dangerous complication. It involves a new blockage in the blood vessels of the lungs, producing chest pain, fever above 38.5°C (101.3°F), coughing or wheezing, and a drop in blood oxygen levels. It can develop on its own or evolve from a pain crisis that started elsewhere. People who experience acute chest syndrome have roughly five times the risk of developing high blood pressure in the lungs and nearly four times the risk of heart failure later in life.
Common Triggers
Crises don’t always come out of nowhere. Several well-known triggers increase the likelihood of an episode:
- Dehydration concentrates the blood and makes sickling more likely. Not drinking enough water, vomiting, or heavy sweating can all set the stage.
- Cold weather and wind exposure are among the most consistently identified triggers in studies. Cold causes blood vessels to constrict, slowing blood flow and giving sickled cells more time to stick together.
- Infections raise the body’s metabolic demand and can directly worsen sickling. They also account for significant differences in how severe the disease is across different parts of the world.
- Intense exercise creates a perfect storm of lactic acid buildup, lower oxygen levels in tissues, and dehydration, all of which promote sickling.
- High altitude reduces the amount of oxygen in the air, which has long been recognized as a concern for people with sickle cell disease.
- Extreme heat can lead to dehydration and trigger a crisis, especially during physical activity.
What a Crisis Feels Like in Children
In infants and toddlers, the first sign of sickle cell disease is often a condition called dactylitis, or hand-foot syndrome. The hands and feet swell painfully as sickled cells block blood flow in the small bones. Fever usually accompanies the swelling. Because very young children can’t describe their pain, unexplained irritability along with puffy hands or feet in an infant known to have sickle cell disease is a red flag.
As children grow, pain episodes shift to the pattern seen in adults, affecting the limbs, back, and chest. The frequency and intensity vary enormously from person to person. Some people have a crisis once every few years; others deal with them monthly.
Long-Term Effects of Repeated Crises
Each crisis isn’t just a painful episode that resolves and leaves no trace. Repeated blockages cause cumulative damage to organs over time. In a large retrospective study, the most common forms of long-term organ damage in people with sickle cell disease were heart failure (7% of patients), neurocognitive problems like memory and concentration difficulties (6%), high blood pressure in the lungs (5%), and chronic kidney disease (5%).
Stroke is a particularly serious risk. People who have had one stroke from sickle cell disease face a dramatically higher chance of having another, and their risk of developing neurocognitive deficits or partial paralysis jumps significantly. Bone damage, blood in the urine, and other organ-specific complications also become more likely the more acute events a person experiences.
Medications That Reduce Crises
Hydroxyurea was the only FDA-approved treatment for sickle cell disease for nearly two decades, from 1998 to 2017. It works by boosting the body’s production of fetal hemoglobin, a form that resists sickling. All adults with sickle cell anemia should at least be offered it. Since 2017, three additional medications have been approved: one that helps red blood cells hold onto oxygen and resist sickling, one that reduces how sticky blood cells are so they’re less likely to clump together, and an amino acid supplement that may help protect red blood cells from damage. Despite these options, real-world use of the newer medications remains low, with one prescribed to fewer than 3% of eligible patients.
Managing Pain at Home and in a Hospital
Mild to moderate pain episodes can sometimes be managed at home with hydration, rest, warmth, and over-the-counter pain relief. Non-medication approaches like massage, yoga, guided relaxation, and TENS units (devices that use mild electrical currents to relieve pain) can also help. Having a plan in place before a crisis strikes makes a significant difference.
For moderate to severe pain, opioid medications are commonly used, though some people have pain that doesn’t respond well to them. In those cases, other approaches including certain anesthetic medications may be added. The CDC recommends seeking care at a facility that specializes in sickle cell disease whenever possible, such as day hospitals or infusion centers, rather than a general emergency department. These facilities are better equipped to evaluate and treat sickle cell pain quickly. If you do need to go to an emergency room, keeping an electronic or printed copy of your individualized pain management plan can help the care team treat you more effectively.