Laboratories Testing for Differentiating Primary from Secondary Thrombocytosis in a Pediatric Patient

When a pediatric patient presents with thrombocytosis, laboratory studies are performed to be able to determine whether it is a condition of primary thrombocytosis or secondary thrombocytosis. No additional studies need to be performed when physicians strongly suspect  primary thrombocytosis . However, several lab testing can help  differentiate secondary from primary thrombocytosis.  Fibrinogen level, acute phase reactants, C-reactive protein, von Willebrand factor and factor VIII are found to be remarkably elevated in pediatric patients with secondary thrombocytosis but normal in case of primary thrombocytosis. In the beginning of reactive thrombocytosis, serum TPO levels can be elevated; But with the progression of the disease TPO can return to normal values. Therefore, it is very important to carefully interpret TPO serum values in a timely manner. Whereas in case of primary thrombocytosis induced by  a mutation in 5’ UTR (5’ untranslated region), which  play a role in inhibition of TPO mRNA,  elevated value of TPO would be present all the time. Nevertheless, essential thrombocytosis due to other mutation can have normal TPO levels.  The most common mutation in essential thrombocytosis is JAK2 mutation, thus when essential thrombocytosis is suspected we always test for JAK2 mutation.

                                           http://spittoon.23andme.com/wp-content/uploads/2012/03/MPN-progression.png

This is an algorithm that presents suggested work-up for platelet count that are over 1 million/μL:

                                                         http://emedicine.medscape.com/article/959378-workup