Comparison of different criteria for the diagnosis of primary myelofibrosis reveals limited clinical utility for measurement of serum lactate dehydrogenase.

Primary myelofibrosis shows histological and pathogenetic overlap with essential thrombocythemia and polycythemia vera. Several diagnostic classifications have been proposed for primary myelofibrosis, although little is known about their clinical utility. In a comparison of three recent classifications, overall concordance was 79%. Inclusion of raised serum lactate dehydrogenase categorized 9% of patients as primary myelofibrosis when other criteria were not met. Although mean serum lactate dehydrogenase levels were higher in patients with primary myelofibrosis, levels were also increased in the majority of patients with essential thrombocythemia or polycythemia vera, and significant overlap was observed. A positive correlation with higher leukocyte and platelet count, and disease duration in primary myelofibrosis, suggests that serum lactate dehydrogenase is a biomarker for disease bulk and/or cellular proliferation. In conclusion, raised lactate dehydrogenase lacks specificity for primary myelofibrosis, consistent with the concept of a phenotypic continuum between essential thrombocythemia, polycythemia vera and primary myelofibrosis.