A new test, the direct antiglobulin consumption test (direct ACT), has been devised to be performed on the leukocytes and platelets of patients. It was performed in parallel with the indirect antiglobulin consumption test (indirect ACT), and other serologic tests on 492 individuals comprising 24 cases of diffuse lupus erythematosus, 93 primary thrombocytopenias, 18 secondary thrombocytopenias, 48 primary leukopenias or leukothrombocytopenias, 80 secondary leukopenias, 101 non-leukothrombocytopenic patients and 128 normal subjects.

A good correlation was obtained between a positive or negative result and the presence or absence of a cytopenia in the corresponding cell series. Out of 183 thrombocytopenic patients, 42.2 per cent gave a positive result with platelets, and out of 128 leukopenic patients, 25.8 per cent gave a positive result on leukocytes, whereas of the 299 patients with normal leukocyte and platelet counts, 98 per cent gave negative results. The test was found positive in three categories of patients:

(1) In diffuse lupus erythematosus, tests on both leukocytes and platelets were almost uniformly positive. The indirect ACT permits a distinction to be made between three substances in the serum of these patients. These are antiplatelet, antileukocyte-cytoplasm and antileukocyte-nuclear substances.

(2) The thrombocytopenic patients were subdivided into two groups, namely primary and secondary thrombocytopenia:

(a) Out of 93 cases of idiopathic thrombocytopenic purpura, about 50 per cent gave a positive result with platelets. Neither the history nor the clinical picture suggested any differentiation between those who gave negative results, apart from the fact that a history of infection was more frequent among the negative cases. Corticosteroid therapy did not affect the result of the test, but following splenectomy, 38 per cent of the cases become negative.

(b) Of 18 patients with a secondary thrombocytopenia, three cases (16 per cent) gave a positive result.

(3) The leukopenic and leukothrombocytopenic patients were also subdivided into two groups:

(a) Out of 48 primary or idiopathic cases, some 50 per cent gave a positive direct ACT either on leukocytes and/or on platelets. By using the indirect ACT it was possible to distinguish two substances in the serum, one being antiplatelet and the other an antileukocyte cytoplasmic substance.

(b) The 80 cases of secondary leukopenia or leukothrombocytopenia gave a positive result in 15 per cent of cases with leukocytes and/ or with platelets.

Of the 101 non-leukothrombocytopenic patients, only five were found to give positive tests.

All the 128 normal subjects gave negative results.

The direct ACT provides direct evidence of the presence of a γ-globulin, probably an auto-antibody, on the leukocytes and/or the platelets of some 99 per cent of cases of diffuse lupus erythematosus, of about 50 per cent of cases of idiopathic thrombocytopenia and idiopathic leukothromobcytopenia, and in about 15 per cent of cases of secondary thrombocytopenia and leukothrombocytopenia. No marked difference was found in the history, clinical picture, or hematological findings between patients giving positive and negative results.

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