Medical Conditions

My Baby's Vascular Tumor Is Causing Blood Clotting Problems (Kasabach-Merritt)

Medically reviewed by Dr. Michael Okonkwo, MD, FAAP · Board-Certified Neonatologist

Content reviewed against published NIH, CHOP, NORD guidelines

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If your baby has been diagnosed with or you suspect vascular tumor is causing blood clotting problems (kasabach-merritt), here is what the evidence says.

The short answer

Kasabach-Merritt phenomenon (KMP) is a rare but serious complication where certain vascular tumors (kaposiform hemangioendothelioma or tufted angioma — not common infantile hemangiomas) trap platelets and clotting factors, leading to dangerously low platelet counts and a bleeding disorder. KMP is a medical emergency that requires hospitalization and specialized treatment. Despite being frightening, modern treatment with sirolimus and other medications has significantly improved outcomes. Most children respond well to treatment, though the vascular tumor may not fully resolve.

Key takeaways

  • Kasabach-Merritt phenomenon (KMP) is a rare but serious complication where certain vascular tumors (kaposiform hemangioendothelioma or tufted angioma — not common infantile hemangiomas) trap platelets and clotting factors, leading to dangerously low platelet counts and a bleeding disorder. KMP is a medical emergency that requires hospitalization and specialized treatment. Despite being frightening, modern treatment with sirolimus and other medications has significantly improved outcomes. Most children respond well to treatment, though the vascular tumor may not fully resolve.
  • Usually normal when: Your baby is being treated for KMP and platelet counts are improving with medication
  • Call your doctor if: Your baby is bleeding (from nose, mouth, or a wound) that does not stop — call 911 or go to the emergency room immediately
  • Varies by age — see the age-by-age breakdown below
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What Parents Should Know

According to NIH, CHOP, NORD guidelines, kasabach-Merritt phenomenon (KMP) is a rare but serious complication where certain vascular tumors (kaposiform hemangioendothelioma or tufted angioma — not common infantile hemangiomas) trap platelets and clotting factors, leading to dangerously low platelet counts and a bleeding disorder. KMP is a medical emergency that requires hospitalization and specialized treatment. Despite being frightening, modern treatment with sirolimus and other medications has significantly improved outcomes. Most children respond well to treatment, though the vascular tumor may not fully resolve. At 0-3 months (acute presentation), kMP typically presents in infancy with a rapidly enlarging, firm, purple vascular mass that becomes painful and tense. The baby may develop bruising, petechiae (tiny red dots on the skin), and signs of bleeding due to severely low platelets. Blood tests show very low platelet counts (often below 10,000) and elevated D-dimer. This is a medical emergency requiring immediate hospitalization. Treatment typically begins with sirolimus and sometimes corticosteroids. It is generally considered normal when your baby is being treated for KMP and platelet counts are improving with medication. However, you should contact your pediatrician promptly if your baby is bleeding (from nose, mouth, or a wound) that does not stop — call 911 or go to the emergency room immediately.

Sources: [1], [2], [3]

Normal vs. Concerning

Usually Normal
Worth Discussing
Your baby is being treated for KMP and platelet counts are improving with medication
Your baby is bleeding (from nose, mouth, or a wound) that does not stop — call 911 or go to the emergency room immediately
The vascular mass is shrinking and becoming softer on treatment
Your baby has a rapidly expanding vascular mass with new bruising — this is a medical emergency
Your child has a residual vascular tumor after KMP resolution and it is being monitored
Your baby develops a high fever while on immunosuppressive medication — seek immediate medical evaluation

When to Seek Immediate Care

  • Your baby is bleeding (from nose, mouth, or a wound) that does not stop — call 911 or go to the emergency room immediately
  • Your baby has a rapidly expanding vascular mass with new bruising — this is a medical emergency
  • Your baby develops a high fever while on immunosuppressive medication — seek immediate medical evaluation
  • Your baby seems very lethargic, pale, or is breathing rapidly — these may be signs of anemia from blood loss and need urgent care

By Age

What to expect by age

0-3 months (acute presentation)

KMP typically presents in infancy with a rapidly enlarging, firm, purple vascular mass that becomes painful and tense. The baby may develop bruising, petechiae (tiny red dots on the skin), and signs of bleeding due to severely low platelets. Blood tests show very low platelet counts (often below 10,000) and elevated D-dimer. This is a medical emergency requiring immediate hospitalization. Treatment typically begins with sirolimus and sometimes corticosteroids.

3-12 months (treatment phase)

Treatment with sirolimus (and sometimes vincristine for resistant cases) usually leads to gradual improvement in platelet counts and shrinkage of the tumor over weeks to months. Blood work is monitored closely. The tumor may change from purple and tense to softer and lighter as it responds to treatment. Side effects of medications are monitored. Most infants respond within 2-4 weeks, though treatment may continue for months to years.

1-3 years (ongoing management)

Even after the KMP resolves (platelets normalize), the underlying vascular tumor often persists as a residual mass. Treatment with sirolimus may continue for an extended period. The vascular anomalies team will determine when it is safe to wean medication. Some residual mass may be managed with compression garments or additional interventions.

3 years+

Long-term follow-up is important. The residual vascular tumor may cause chronic pain, limb length discrepancy, or cosmetic concerns. Physical therapy may be needed if a limb is affected. Most children who survive the acute KMP episode do well long-term, though they need continued monitoring by a vascular anomalies center.

What to Tell Your Pediatrician

  • Describe when you first noticed vascular tumor is causing blood clotting problems (kasabach-merritt) and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if the vascular mass seems to be growing or becoming more purple and tense again.
  • Mention if your baby is developing new bruises or petechiae while on treatment.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

What Should You Do?

When to take action

Probably normal when...
  • Your baby is being treated for KMP and platelet counts are improving with medication
  • The vascular mass is shrinking and becoming softer on treatment
  • Your child has a residual vascular tumor after KMP resolution and it is being monitored
Mention at your next visit when...
  • The vascular mass seems to be growing or becoming more purple and tense again
  • Your baby is developing new bruises or petechiae while on treatment
  • The mass is causing your baby pain or discomfort
  • You have questions about how long treatment needs to continue
Act now when...
  • Your baby is bleeding (from nose, mouth, or a wound) that does not stop — call 911 or go to the emergency room immediately
  • Your baby has a rapidly expanding vascular mass with new bruising — this is a medical emergency
  • Your baby develops a high fever while on immunosuppressive medication — seek immediate medical evaluation
  • Your baby seems very lethargic, pale, or is breathing rapidly — these may be signs of anemia from blood loss and need urgent care

What You Can Do at Home

  • Keep track of when you notice vascular tumor is causing blood clotting problems (kasabach-merritt) — noting the time of day, duration, and any triggers can help your pediatrician.
  • Remember that your baby is being treated for KMP and platelet counts are improving with medication — this is generally within the range of normal.
  • At 0-3 months (acute presentation), focus on observation rather than intervention unless your pediatrician advises otherwise.
  • Follow any care instructions from your pediatrician. Keep a written log of symptoms to bring to appointments.
  • While monitoring at home, seek immediate care if your baby is bleeding (from nose, mouth, or a wound) that does not stop — call 911 or go to the emergency room immediately.

My Baby Has a Vascular Malformation (Port-Wine Stain or Deeper)

Vascular malformations are structural abnormalities of blood vessels or lymph vessels that are present at birth (though some become apparent later). Unlike hemangiomas, which grow rapidly and then shrink, vascular malformations grow proportionally with the child and do not go away on their own. They are classified by the type of vessel involved: capillary (port-wine stains), venous, lymphatic, or arteriovenous. Most are benign and manageable, but the approach depends on the type, location, and whether associated conditions are present (such as Sturge-Weber syndrome with facial port-wine stains).

Milestone

Month-by-Month Development

Detailed monthly development guides from birth through 24 months.

Guide

When to Call the Doctor

General guide on when to call the pediatrician, visit urgent care, or go to the ER.

Frequently asked questions

Is vascular tumor is causing blood clotting problems (kasabach-merritt) normal?
Kasabach-Merritt phenomenon (KMP) is a rare but serious complication where certain vascular tumors (kaposiform hemangioendothelioma or tufted angioma — not common infantile hemangiomas) trap platelets and clotting factors, leading to dangerously low platelet counts and a bleeding disorder. KMP is a medical emergency that requires hospitalization and specialized treatment. Despite being frightening, modern treatment with sirolimus and other medications has significantly improved outcomes. Most children respond well to treatment, though the vascular tumor may not fully resolve.
When should I call the doctor about vascular tumor is causing blood clotting problems (kasabach-merritt)?
Your baby is bleeding (from nose, mouth, or a wound) that does not stop — call 911 or go to the emergency room immediately Your baby has a rapidly expanding vascular mass with new bruising — this is a medical emergency Your baby develops a high fever while on immunosuppressive medication — seek immediate medical evaluation
When is vascular tumor is causing blood clotting problems (kasabach-merritt) normal?
Your baby is being treated for KMP and platelet counts are improving with medication The vascular mass is shrinking and becoming softer on treatment Your child has a residual vascular tumor after KMP resolution and it is being monitored
What causes vascular tumor is causing blood clotting problems (kasabach-merritt)?
Kasabach-Merritt phenomenon (KMP) is a rare but serious complication where certain vascular tumors (kaposiform hemangioendothelioma or tufted angioma — not common infantile hemangiomas) trap platelets and clotting factors, leading to dangerously low platelet counts and a bleeding disorder. KMP is a medical emergency that requires hospitalization and specialized treatment. Despite being frightening, modern treatment with sirolimus and other medications has significantly improved outcomes. Most children respond well to treatment, though the vascular tumor may not fully resolve. Common explanations include: Your baby is being treated for KMP and platelet counts are improving with medication. The vascular mass is shrinking and becoming softer on treatment.
What should I mention to my pediatrician about vascular tumor is causing blood clotting problems (kasabach-merritt)?
You should mention vascular tumor is causing blood clotting problems (kasabach-merritt) at your next visit if: The vascular mass seems to be growing or becoming more purple and tense again. Your baby is developing new bruises or petechiae while on treatment. The mass is causing your baby pain or discomfort.
Is vascular tumor is causing blood clotting problems (kasabach-merritt) normal at 0-3 months (acute presentation)?
KMP typically presents in infancy with a rapidly enlarging, firm, purple vascular mass that becomes painful and tense. The baby may develop bruising, petechiae (tiny red dots on the skin), and signs of bleeding due to severely low platelets. Blood tests show very low platelet counts (often below 10,000) and elevated D-dimer. This is a medical emergency requiring immediate hospitalization. Treatment typically begins with sirolimus and sometimes corticosteroids.
Is vascular tumor is causing blood clotting problems (kasabach-merritt) normal at 3-12 months (treatment phase)?
Treatment with sirolimus (and sometimes vincristine for resistant cases) usually leads to gradual improvement in platelet counts and shrinkage of the tumor over weeks to months. Blood work is monitored closely. The tumor may change from purple and tense to softer and lighter as it responds to treatment. Side effects of medications are monitored. Most infants respond within 2-4 weeks, though treatment may continue for months to years.
Should I go to the ER for vascular tumor is causing blood clotting problems (kasabach-merritt)?
Seek emergency care if your baby is bleeding (from nose, mouth, or a wound) that does not stop — call 911 or go to the emergency room immediately, or if your baby has a rapidly expanding vascular mass with new bruising — this is a medical emergency. When in doubt, call your pediatrician's after-hours line for guidance.
Does vascular tumor is causing blood clotting problems (kasabach-merritt) go away on its own?
In many cases, vascular tumor is causing blood clotting problems (kasabach-merritt) resolves on its own, especially when your baby is being treated for KMP and platelet counts are improving with medication. By 3 years+, long-term follow-up is important. The residual vascular tumor may cause chronic pain, limb length discrepancy, or cosmetic concerns. Physical therapy may be needed if a limb is affected. Most children who survive the acute KMP episode do well long-term, though they need continued monitoring by a vascular anomalies center.
NIHCHOPNORD

References

  1. [1]National Library of Medicine. Kasabach-Merritt Phenomenon: Pathogenesis and Management. Blood, 2022. NIH
  2. [2]Children's Hospital of Philadelphia. Kaposiform Hemangioendothelioma. CHOP
  3. [3]National Organization for Rare Disorders. Kasabach-Merritt Syndrome. NORD

Doctor Visit Checklist

Bring this checklist to your next pediatrician visit to discuss My Baby's Vascular Tumor Is Causing Blood Clotting Problems (Kasabach-Merritt).

Things to mention

  • Describe when you first noticed vascular tumor is causing blood clotting problems (kasabach-merritt) and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if the vascular mass seems to be growing or becoming more purple and tense again.
  • Mention if your baby is developing new bruises or petechiae while on treatment.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

Observations to share

  • The vascular mass seems to be growing or becoming more purple and tense again
  • Your baby is developing new bruises or petechiae while on treatment
  • The mass is causing your baby pain or discomfort

Urgent signs to report immediately

  • Your baby is bleeding (from nose, mouth, or a wound) that does not stop — call 911 or go to the emergency room immediately
  • Your baby has a rapidly expanding vascular mass with new bruising — this is a medical emergency
  • Your baby develops a high fever while on immunosuppressive medication — seek immediate medical evaluation

My notes

From ismybabyalright.com — free, evidence-based baby health guides

All content follows our editorial policy and is reviewed against published clinical guidelines.

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Bottom line

Most cases of vascular tumor is causing blood clotting problems (kasabach-merritt) are normal. Talk to your pediatrician if your baby is bleeding (from nose, mouth, or a wound) that does not stop — call 911 or go to the emergency room immediately.

Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.

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