We have investigated the effects of 1-desamino-8-D-arginine
vasopressin (
DDAVP) infusion on platelet count and bleeding time in 4 patients with type IIB
von Willebrand's disease (vWd). Three of four patients showed a normalization of the bleeding time within 1 h after the infusion, while bleeding time was not modified in the fourth. In accordance with the literature,
thrombocytopenia was observed after
DDAVP infusion, but this
thrombocytopenia was due to the
anticoagulants used for blood collection. In two patients (F.I., G.F.) no
thrombocytopenia was observed when platelets were counted by fingerstick method but there was a 20% platelet decrease in blood samples collected in
sodium citrate and a 50% decrease in samples collected in
EDTA. Dramatic falls in platelet counts (70-95%) were observed in the additional two patients (C.A., D.Z.) after
DDAVP infusion, when both
sodium citrate or
EDTA were used as
anticoagulants. In the latter two patients there was also a 50% decrease in platelet count when the fingerstick method was used. The decrease in the patient's platelet count in
EDTA samples after
DDAVP infusion could be prevented, in part, by the previous additions of an anti GPIb
monoclonal antibody and an anti GPIIb-IIIa
monoclonal antibody. Thus, the
thrombocytopenia observed in the four IIB vWd patients studied after
DDAVP infusion seems to be, at least partially, a pseudothrombocytopenia depending on the
calcium concentration in the blood samples and the availability of GPIb and
GPIIb-IIIa receptors. These findings and the normalization of the bleeding time observed in three of the four patients has led us to reconsider the possible use of
DDAVP in the treatment of our IIB vwd patients.