In both children and adults, ITP is a diagnosis of exclusion.1 A differential diagnosis must include all disorders that can present with a low platelet count.2 The appearance of signs and symptoms—such as petechiae and purpura—is determined primarily by the platelet count at the time of presentation.
| Platelet count | Signs/symptoms of ITP3 |
| >50,000/µL | Incidental finding (eg, via routine blood work) |
| 30,000-50,000/µL | Bruising with minor trauma |
| 10,000-30,000/µL | Spontaneous petechiae or ecchymoses, prolonged bleeding with trauma, menorrhagia |
| <10,000/µL | Mucosal bleeding; at risk for central nervous system bleeding |
Before a definitive diagnosis can be made, the following disorders must be distinguished from ITP (dependent on diagnostic criteria):4
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The diagnostician may also wish to consider possibilities such as pernicious anemia or infiltrative disorders (eg, Gaucher’s disease).5
Apart from any bleeding and bruising issues, the clinical history and physical examination may be normal.2 Splenomegaly is not characteristic of ITP.2 Blood counts and a peripheral blood smear may be normal, with some exceptions (see below).2
Algorithm for investigation of isolated thrombocytopenia in an otherwise healthy person (adapted from reference 6, with permission)
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| Peripheral smear in a patient with ITP showing an almost total absence of platelets. |
Further diagnostic studies may be considered, including detection of antinuclear antibody (ANA), HIV testing (if risk factors are present), and thyroid function testing (before splenectomy).7,8
Read more about ITP and hepatitis C
Biopsy and Aspiration of Bone Marrow
Opinions differ on the benefits of bone marrow biopsy and aspiration for the evaluation of ITP, but it is generally done to rule out other causes of thrombocytopenia.7 The 2003 guidelines from the British Committee for Standards in Haematology and General Haematology Task Force (BCSH) suggest a bone marrow biopsy and aspirate examination to confirm diagnosis in the following cases of adult ITP:
Some leading investigators also suggest a biopsy for adult patients who do not respond to primary treatment.10 If it is performed, the marrow of an ITP patient shows an increased number of small, immature megakaryocytes.
| Bone marrow showing an immature megakaryocyte with cytoplasmic budding. Young megakaryocytes are seen in increased numbers in ITP. |
References
1. Cines DB, Blanchette VS. Immune thrombocytopenic purpura. N Engl J Med. 2002;346(13):995-1008.
2. Chong BH, Ho S-J. Autoimmune thrombocytopenia. J Thromb Haemost. 2005;3(8):1763-1772.
3. McMillan R. Therapy for adults with refractory chronic immune thrombocytopenic purpura. Ann Intern Med. 1997;126(4):307-314.
4. George JN, Kojouri K. Immune thrombocytopenic purpura. In: Kitchens CS, Alving BM, Kessler CM, eds. Consultative Hemostasis and Thrombosis. 2nd ed. Philadelphia, PA: WB Saunders; 2007; 37-38.
5. Rajan SK, Espina BM, Liebman HA. Hepatitis C virus-related thrombocytopenia: clinical and laboratory characteristics compared with chronic immune thrombocytopenic purpura. Br J Haematol. 2005;129(6):818-824.
6. George JN. Platelets. Lancet. 2000;355(9214):1531-1539.
7. Cooper N, Bussel J. The pathogenesis of immune thrombocytopaenic purpura. Br J Haematol. 2006;133(4):364-374.
8. George JN, Woolf SH, Raskob GE, et al. Idiopathic thrombocytopenic purpura: a practice guideline developed by explicit methods for the American Society of Hematology. Blood. 1996;88(1):3-40.
9. Harrison’s Principles of Internal Medicine. 16th ed. Kasper DL, Fauci AS, Longo DL, Braunwald E, Hauser SL, Jameson JL, eds. New York, NY: The McGraw-Hill Companies, Inc.; 2005:675.
10. British Committee for Standards in Haematology General Haematology Task Force. Guidelines for the investigation and management of idiopathic thrombocytopenic purpura in adults, children and in pregnancy. Br J Haematol. 2003;120(4):574-596.
11. Cines DB, Bussel JB. How I treat idiopathic thrombocytopenic purpura (ITP). Blood. 2005;106(7):2244-2251.
