IVIG is approved by the FDA for use in the treatment of the following diseases: Kawasaki disease, dermato/polymyositis, idiopathic thrombocytopenic purpura (ITP), Guillain-Barre syndrome, polyneuropathy, some viral diseases, and some forms of immune deficiency. The place of IVIG in the treatment of ITP is not well clarified. It does not modify the disease as do steroids and splenectomy, but only gains a temporary rise in platelet counts, until definitive therapy can be planned or accomplished. In addition, a number of alternatives exist, including: Anti-RhoD, vincristine, Rituximab, danazol, high dose pulse steroids and even chemotherapy. IVIG is accordingly best used as a temporary measure, to prepare the patient for spenectomy or while discussions of other treatments take place. It is also occasionally used to wait and see if a spontaneous remission of the ITP occurrs; however, this use is less supported by the literature.
Based on the literature, CMS advises the following:IVIG is indicated for chronic ITP only when all of the following conditions are met:

Prior treatment with corticosteroids and splenectomy;
Duration of illness less than 6 months;
Age of 10 years or older;
No concurrent illness/disease explaining thrombocytopenia; and
Platelet counts persistently at or below 20,000/ml.

The Australian guideline sets the plt. level at 30K and adds preoperative use and use in preagnant women as well as for severe bleeding and other indications.

Anderson D, Ali K, Blanchette V, et al. Guidelines on the use of intravenous immune globulin for hematologic conditions. Transfus Med Rev. 2007;21(2 Suppl 1):S9-56.

George JN, Woolf SH, Raskob GE, Wasser JS, Aledort LM, Ballem PJ, Blanchette VS, Bussel JB, Cines DB, Kelton JG, Lichtin AE, McMillan R, Okerbloom JA, Regan DH, Warrier I: Idiopathic thrombocytopenic purpura: A practice guideline developed by explicit methods for the American Society of Hematology. Blood 88:3, 1996

Download 2011 ITP Pocket Guide[1]

Cines DB, Blanchette VS: Immune thrombocytopenic purpura. N Engl J Med 2002 Mar 28; 346(13): 995-1008

Kahn MJ, McCrae KR: Splenectomy in Immune Thrombocytopenic Purpura: Recent Controversies and Long-term Outcomes. Curr Hematol Rep 2004 Sep; 3(5): 317-23

McMillan R, Durette C: Long-term outcomes in adults with chronic ITP after splenectomy failure. Blood 2004 Aug 15; 104(4): 956-60

Australian Guideline(2007)

http://www.nba.gov.au/ivig/pdf/criteria-qrg.pdf

Alan H. Lazarus^{* Mechanism of action of IVIG in ITP} 2002 Blackwell Science Ltd  Vox Sanguinis Volume 83, Issue Supplement s1, pages 53–55, August 2002

D . Anderson , K . Ali , V . Blanchette , M . Brouwers , S . Couban , P . Radmoor , L . Huebsch , H . Hume , A . McLeod , R . Meyer Guidelines on the Use of Intravenous Immune Globulin for Hematologic Conditions .  Transfusion Medicine Reviews , Volume 21 , Pages S9 – S56 2007

Munehiro Honda, ISRN EndocrinologyVolume 2011 (2011), Successful Treatment of Methimazole-Induced Severe Aplastic Anemia by Granulocyte Colony-Stimulating Factor, Methylprednisolone, and Cyclosporin