What Causes Thrombocytosis?

Patient Presentation

A 17-month-old male came to clinic with a rash on his left leg. The patient had been well except for recent upper respiratory infection symptoms for the past 2 weeks. The past medical history was negative. The review of systems showed no fever, emesis, weight changes, sweating, or fatigue.

The pertinent physical exam showed a well-appearing toddler with normal vital signs and growth parameters between 50-90%. HEENT had shoddy anterior cervical lymph nodes and moderate rhinorrhea. Abdomen was negative. His skin examination revealed an area of petechiae on the inner left lower leg. He had some mild bruising on bilateral shins in different states of healing. He had no other lesions. Lymph nodes were negative on the rest of the body except for shoddy inguinal nodes bilaterally. The laboratory evaluation revealed a complete blood count with a hemoglobin of 11.2 mg/dl, white blood cell count of 20.8 x 1000/mm2 and platelets of 180,000 . The laboratory technologist called to say that the platelet count was not reported normally because the platelets were in clusters and the estimated count was more than 1 million. Additionally, many of the white blood cells appeared to be uniform blue cells. The smear was being sent for pathologist’s review because of the abnormalities including the possibility of a malignancy. Liver function tests and viral panels were also sent.

During the patient’s clinical course, the physician contacted a hematologist with an appointment the next day. During that visit, the hematologist confirmed the petechiae which had not spread over the night. Another complete blood count had a white blood cell count of 18.3 x 1000/mm2 and 740,000 platelets. The blood smear review showed many white blood cells that were reactive but did not appear malignant and some of the platelets were in clusters but many more were not. The liver function tests had very mild transaminase elevation, and the viral panel was positive for cytomegalovirus. This was felt to be the presumed diagnosis and the patient was followed. Over the next two weeks, the laboratory tests normalized and the patient was doing well.

Cytomegalovirus (CMV) belongs to the herpes virus family. It can be acquired though contact with infected body fluids and cause primary infection. It can also become latent and then reactivated. It is also possible to become infected with another CMV strain.

Primary maternal CMV infection has a 30-40% risk of transplacental transmission to the fetus, and if infected a 20-25% risk of some type of developmental problems in the child. Most congenitally infected infants have no symptoms at birth but 5-15% will have sequelae such as hearing loss, vision problems or mental retardation. If affected at birth, common symptoms include growth retardation, microcephaly, hepatosplenomegaly, jaundice, anemia, thrombocytopenia, petechiae and chorioretinitis. Death occurs in 20-30% of affected infants. Additionally, in transplant patients or patients with immunodeficiency, CMV can be a major cause of morbidity and mortality.

Immunocompetent children and adults usually have no symptoms and no long-term problems. Flu-like symptoms can occur including fever, malaise, myalgia, cervical lymphadenopathy and sometimes pneumonia or hepatitis.

Extreme hyperthombocytosis is generally defined as > 1 million platelets. It does occur but usually only in a small percentage of cases (0.5%).

Learning Point

The differential diagnosis of thrombocytosis includes:

  • Reactive
    • Anemia, iron deficiency
    • Arthritis, rheumatoid
    • Bacterial infection
    • Inflammatory bowel disease
    • Post-splenectomy or functional asplenia
    • Rebound after drugs/alcohol
    • Surgery
    • Trauma
  • Myelodysplastic disorder
    • Acute myelogeous leukemia
    • Chronic myelogenous leukemia
    • Essential thrombocythemia
  • Von Willebrand type II
  • Artificial
    • Cryoglobulinemia
    • Cytoplasmic fragments
    • Pseudohyperkalemia

Extreme or hyperthrombocytosis

  • Infection – 31%
  • Postsplenectomy or hyposplenism – 19%
  • Malignancy – 14%
  • Trauma – 14%
  • Inflammation (noninfectious) – 9%
  • Blood loss – 6%
  • Rebound thrombocytosis – 3%
  • Uncertain – 4%

Questions for Further Discussion
1. What causes leukocytosis?
2. What causes thrombocytopenia? See “What is the Approach to a Child with Thrombocytopenia?”

Related Cases

    Symptom/Presentation: Rash

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for these topics: Cytomegalovirus Infections and Platelet Disorders.

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

Wiedmeier SE, Henry E, Burnett J, Anderson T, Christensen RD. Thrombocytosis in neonates and young infants: a report of 25 patients with platelet counts of > or = 1000000 microl(-1). J Perinatol. 2010 Mar;30(3):222-6.

Chiarello P, Magnolia M, Rubino M, Liguori SA, Miniero R. Thrombocytosis in children. Minerva Pediatr. 2011 Dec;63(6):507-13.

Tefferi A. Approach to the Paitent with Thrombocytosis. Up to Date.
Available from the Internet at http://www.uptodate.com.proxy.lib.uiowa.edu/contents/approach-to-the-patient-with-thrombocytosis?source=search_result&search=thrombocytosis&selectedTitle=1%7E150 (rev. 9/6/2012, cited 10/16/2012).

Yinon Y, Farine D, Yudin MH et. al. Cytomegalovirus in Pregnancy. SOGC Clinical Practice Guideline. JOGC 2010;348-353.

ACGME Competencies Highlighted by Case

  • Patient Care
    1. When interacting with patients and their families, the health care professional communicates effectively and demonstrates caring and respectful behaviors.
    2. Essential and accurate information about the patients’ is gathered.
    3. Informed decisions about diagnostic and therapeutic interventions based on patient information and preferences, up-to-date scientific evidence, and clinical judgment is made.
    4. Patient management plans are developed and carried out.
    7. All medical and invasive procedures considered essential for the area of practice are competently performed.
    8. Health care services aimed at preventing health problems or maintaining health are provided.
    9. Patient-focused care is provided by working with health care professionals, including those from other disciplines.

  • Medical Knowledge
    10. An investigatory and analytic thinking approach to the clinical situation is demonstrated.
    11. Basic and clinically supportive sciences appropriate to their discipline are known and applied.


    Donna M. D’Alessandro, MD
    Professor of Pediatrics, University of Iowa Children’s Hospital