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.