A Method for the Fluorimetric Determination of Vitamin A

¹¹¹In-labelled platelets were used for analysing platelet dynamics in 43 patients with idiopathic thrombocytopenic purpura (ITP). The detected time-activity curves, recorded with a gamma camera, were analysed by three methods: two-and three-compartment models, and an open model in which only the splenic curve was analysed. In the two-compartment model the mean rate constant from blood to spleen was 0.328±0.028 min^-1 (mean±SEM) and from spleen to blood 0.061±0.007 min^-1, whereas in the three-compartment model the corresponding values were 0.236±0.020 and 0.044±0.007 min^-1, respectively. The mean rate constant from blood to liver was 0.466+0.149 min¹ and from liver to blood 0.341±0.106 min^-1 as derived from the three-compartment model. The rate constant from spleen to blood, as determined from the three-compartment model, was significantly higher in patients with a strongly positive result for platelet-associated auto-antibodies (platelet suspension immunofluorescence test (PSIFT)) than in patients with a negative PSIFT. The mean hepatic net rate in patients with a high level of antibodies is into the liver, while in patients with little or no antibodies the net rate is into the blood pool. The mean half-life for the fast component of the inverted splenic curve was 2.5±0.2 min and for the slow component 16±2 min. In patients with a strongly positive PSIFT the half-life for the slow component was significantly longer than in patients with a negative PSIFT. We, therefore, conclude that equilibrium in the exchange of platelets between the spleen and blood is reached more rapidly in patients with a strongly positive PSIFT than in patients with a negative PSIFT.