Polycythemia laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Debduti Mukhopadhyay, M.B.B.S[2], Zaida Obeidat, M.D.
Overview
Polycythemia is determined by the increase of hematocrit and hemoglobin. Causes are physiologic polycythemia (this form can be found in highlanders and athletes training at high altitude), neoplastic diseases (polycythemia vera with proliferation of a cell clone), or can be resulting from chronic hypoxemia.
Laboratory findings
The workup of polycythemia begins with ruling out polycythemia vera (PV), which is a neoplastic clonal blood disorder with autonomous (EPO-independent) erythroid proliferation that results in down regulation of EPO production and low or normal serum EPO levels. All patients should initially be tested for the V617F mutation in exon 14 of the Janus kinase 2 (JAK2) gene. The presence of a JAK2 V617F mutation has a sensitivity of 97% and specificity of 100% for distinguishing polycythemia vera from other causes of polycythemia.
Laboratory tests that help to the diagnosis of the underlying cause of polycythemia include:
- Complete Blood Count (CBC):
-Increased white blood cells and platelets
-Increased hemoglobin levels
-Increased hematocrit levels
- Red Cell Mast Test:
This procedure is used to measure the volume (amount) of red blood cells in relation to the volume of plasma (fluid) in whole blood. In patients with PV, there may be an absolute increase in red blood cell mass. This test is infrequently performed in the United States due to high cost, difficulty obtaining the appropriate test materials, and the advent of new blood tests such as mutational testing
- Peripheral Blood Smear:
A procedure in which a blood sample is viewed under a microscope. A pathologist examines the sample to see if there are any unusual changes in the size, shape and appearance of various blood cells. The test also checks for the presence of immature (blast) cells in the blood.
- Comprehensive Metabolic Panel:
For patients suspected of having PV, it is important to test the serum erythropoietin level. Erythropoietin is a hormone naturally produced by the kidneys to stimulate the production of new red blood cells. Individuals with PV usually have very low levels of erythropoietin.
- Bone Marrow Tests
- Bone marrow aspiration
- Bone marrow biopsy
In PV, the bone marrow shows above-normal numbers of blood cells and an abnormal number of the platelet-forming cells called “megakaryocytes” in the bone marrow. The pathologist also examines the chromosomes of the bone marrow cells to rule out other blood diseases.
Molecular genetic tests are very sensitive tests that look for specific gene mutations. If PV is suspected, molecular testing for the JAK2 mutation should be performed. The JAK2 V617F mutation is found in more than 90 percent of PV patients. The U.S. Food and Drug Administration (FDA) has approved a test called ipsogen JAK2 RGQ PCR Kit to detect mutations affecting the Janus Tyrosine Kinase 2 (JAK2) gene. This test is intended to help doctors evaluate patients for suspected PV.
Polycythemia Vera Study Group Diagnostic Criteria for Polycythemia Vera:
- Major criteria:
1-Total red blood cell mass in males, >/=36ml/kg; I females, >/=32ml/kg
2-Arteial oxygen saturation >/=92%
3-Splenomegaly
- Minor criteria:
1-Thrombocytosis with platelet count >400000µl
2-Leukocytosis with a white blood cell count >12000/µl
3-Increased leukocyte alkaline phosphatase >100U/L
4-Serum vitamin B12 concentration greater than 900pg/ml or binding capacity >2200pg/ml
- Diagnosis of polycythemia vera is established with all major criteria or first 2 major criteria plus any 2 minor criteria.
World Health Organization diagnostic criteria for Polycythemia Vera:[1]
- A1 Elevated RBC mass>25% above mean normal predicted value, or Hb>18.5g/dl in men, 16.5g/dl in women
- A2 No cause of secondary Erythrocytosis include absence of familial Erythrocytosis; no elevation of erythropoietin due to hypoxia (arterial PO2</= 92%), high oxygen affinity hemoglobin, truncated erythropoietin receptors, inappropriate erythropoietin production by tumor
- A3 Splenomegaly
- A4 Clonal genetic abnormality other than Ph chromosome or BCR/ABL fusion gene in marrow cells
- A5 Endogenous erythroid colony formation in vitro
- B1 Thrombocytosis >400x10ª/L
- B2 WBC >12x10ª/L
- B3 Bone marrow biopsy showing panmyelosis with prominent erythroid and megakaryocytic proliferation
- B4 Low serum EPO levels
Polycythemia diagnosed when A1 + A2 any other A or A1 + A2 + any other 2B. RBC indicated red blood cell; Hb, hemoglobin; Ph, Philadelphia; WBC, white blood cell; and EPO, erythropoietin.
- ↑ Cao M, Olsen RJ, Zu Y (2006). "Polycythemia vera: new clinicopathologic perspectives". Arch Pathol Lab Med. 130 (8): 1126–32. doi:10.1043/1543-2165(2006)130[1126:PV]2.0.CO;2. PMID 16879013.