[Implementation of the immunological method for improvement on accurate platelet counts]

Rapid and accurate platelet counting is clinically required in severe thrombocytopenia. Prophylactic platelet transfusions are usually indicated in thrombocytopenia with platelet counts less than 20,000/microliter. It was recently reported that the confidence lower limit of platelet counts by automated blood cell counter is about 14,000/microliter. Clinical blood samples occasionally contain red-cell fragments or large platelets. In these cases, platelets should be counted by the phase-contrast microscopy. However, this manual operation is accurate but not precise and needs complicated technique. Abbott has developed an immunological platelet counting method by CELL-DYN 4000. We measured platelet counts in 137 blood samples from thrombocytopenic patients. These samples included red-cell fragmentation and large platelets on blood smears. We compared platelet counts with the immunological method(PLTimm) to those with Brecher-Cronkite, the optical(PLTo) and the impedance method(PLTi). PLTimm correlated more closely with the phase-contrast microscopy counts than PLTo or PLTi. In patients with microangiopathic hemolytic anemia, PLTo or PLTi could not exclude red-cell fragments, but PLTimm absolutely excluded red-cell fragments. In patients with giant platelets, PLTo or PLTi could not include large platelets but PLTimm included them and coincided well with platelet counts by the phase-contrast microscopy. These results indicate that the immunological method by CELL-DYN 4000 appears to be accurate and a very useful method for accurate platelet counts in severe thrombotybopenia.