Sysmex XN-1000 hematology analyzer is widely used and reliable analyzer in hematology laboratories. Goal of this research was to check the limit of quantification (LoQ) of leukocytes using „low white blood cell“ mode which is being used ever more frequently, especially for samples of immunosupressed pacients. Therefore, it is very important that laboratory personnel knows which given value can be validated as accurate and precise. Also, as part of our research, we have checked the limit of quantification of platelets in whole blood mode. To determine limit of quantification of leukocytes we used native samples which had extremely low leukocyte count (<0,2x10^9/L), as well as samples with higher white blood cell count (>1x10^9/L) dilluted with plasma, so it would be as close to matrix of a native sample. „Low-WBC“ mode uses so called WDF channel. It performs every measurement in triplicate which increases procedure accuracy. Dilution of samples for measurements of platelet count was made using plasma obtained by twicely repeated centrifuge at 4000 rpm. Firstly, we have measured the limit of blank (LoB), it turned out to be 0.00 x10^9/L. Leukocyte limit of quantification was determined experimentally, by continuouns measurements of ever lower leukocyte concentracions (1.0, 0.8, 0.5, 0.2, 0.1, 0.09, 0.07, 0.05, 0.03) x10^9/L. Furthermore, using the previously agreed criteria for highest acceptable impreccision and inaccuracy (bias and CV) of 10% we determined the leukocyte LoQ at 0.1x10^9/L. Using the same criteria the platelet LoQ was determined at 5x10^9/L after testing series of samples of (60, 10, 5, 3)x10^9/L. Comparing our test results and dana provided by Sysmex XN-1000 manual, we have concluded that the leukocyte LoQ results match the data provided by the producer. Result of platelet LoQ was even better than the one provided (at 10x10^9/L), using our criteria of accepting 10% bias and CV. To conclude, these findings are very useful in day-to-day practise, especially for the specialized laboratories of medical institutions that take care of a large number of oncological patients.