<prompt> A 59-year-old male came with Hb 18.0 gmdl on three occasions. The resident doctor wants to exclude Polycythemia Vera. Which of the following is the most relevant investigation :HematocritTotal leukocyte countRed cell massReticulocyte count  <response>: Answer is C Red cell mass: When confronted with an elevated Haemoglobin or Haematocrit the first step should be to determine whether this increase is due to absolute erythrocytosis or relative erythrocytosis. Absolute erythrocytosis Relative spurious erythrocytosis Apparent increase in red cell mass due to reduction in plasma volume True increase in red cell mass Red cell mass is the investigation of choice to determine such distinction. Once red cell mass determination confirms absolute erythrocytosis, a diagnosis of polycythemia vera can be established by demonstrating absence of elevation in serum erythropoetin levels. 