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Increased red blood cell count may result from primary erythrocytosis (polycythemia vera), but it is often due to secondary causes with increased erythropoietin levels. Secondary erythrocytosis may also be congenital due to different gene mutations of hemoglobin, hemoglobin stabilization proteins, EPO receptors, or oxygen sensing pathways. Von Hippel- Lindau gene mutation causes altered tissue oxygen sensation in VHL disease, usually with normal hemoglobin. Germline VHL mutations associate with classical VHL disease and represent genetic susceptibility for pheochromocytoma. VHL polymorphisms are mostly considered an innocent phenomenon. Still, some data indicate that these polymorphisms are not always harmless and can occur with prostate, renal, and colon cancer or even with isolated erythrocytosis. Seventy-eight patients referred to our department with elevated hemoglobin were screened for VHL mutations. There were no classical somatic VHL mutations. However, we found heterozygous (GA) or homozygous (AA) rs779805 VHL c.-195G>A polymorphism accompanied by erythrocytosis. These patients are Jak-2 negative, with normal or elevated EPO levels, sometimes with family accumulations and often phlebotomy needs, and in some cases with malignancies in the family. No other cause of erythrocytosis was found. We use phlebotomy regularly, and for those with cardiovascular risk factors, we recommend aspirin.

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A new liquid-borne particle counter is described that utilizes an optimized optical set-up to determine the size distribution and concentration by two different methods and to estimate the shape-factor of the suspended particles. The aim of this optimization was to achieve the appropriate optical conditions for such type of measurement, viz.determining the geometry of the illumination and detection, and calculating the testing volume and dependence of the parameters of detected signal on the particle size for pulse height and pulse duration methods performed at the same illumination and detection conditions. The main benefit of the developed device is the high dynamic range of the size determination of the micron-size liquid-borne particles and the possibility of estimating their shape-factor. The proposed measurement method was incorporated in a PC-controlled LQB-1-200-L-T liquid-borne laser particle counter developed on the basis of previous APC -03-2 and APC-03-2A air-borne particle counters and a LQB-1-200 liquidborne particle counter.

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