Dehydration: This condition can cause an elevated hematocrit due to a decrease in plasma volume, which concentrates the red blood cells. An elevated MCV (mean corpuscular volume) indicates that the red blood cells are larger than normal, and a low MCHC (mean corpuscular hemoglobin concentration) suggests that these larger cells have less hemoglobin than they should, which can be seen in dehydration due to the relative increase in cell size without a proportional increase in hemoglobin content.

Polycythemia Vera: A myeloproliferative disorder that leads to an overproduction of red blood cells, which can cause an elevated hematocrit. The MCV can be elevated due to the variability in red blood cell size, and the MCHC might be low if the increase in red blood cell mass outpaces the increase in hemoglobin production.
Vitamin B12 or Folate Deficiency: These deficiencies can lead to megaloblastic anemia, characterized by large red blood cells (elevated MCV) and often a low MCHC due to impaired DNA synthesis affecting hemoglobin production. However, the hematocrit might not always be elevated in these conditions unless there's a compensatory mechanism or another underlying condition.

Carbon Monoxide Poisoning: Although less common, carbon monoxide poisoning can lead to an elevated hematocrit due to carboxyhemoglobin formation, which can falsely elevate the hematocrit measurement. The MCV might be elevated due to the binding of carbon monoxide to hemoglobin, and the MCHC could be low due to the displacement of oxygen and the formation of carboxyhemoglobin.
Chronic Lung Disease: Conditions like chronic obstructive pulmonary disease (COPD) can lead to secondary polycythemia due to chronic hypoxia, which stimulates erythropoietin production and increases red blood cell production, potentially elevating the hematocrit. The MCV and MCHC findings could vary but might fit the described pattern in some cases.

Myelodysplastic Syndromes: Certain types of myelodysplastic syndromes can present with an elevated hematocrit, elevated MCV due to dysplastic changes in red blood cells, and a low MCHC due to ineffective erythropoiesis and hemoglobinization.
Red Blood Cell Membrane Disorders: Disorders affecting the red blood cell membrane, such as hereditary spherocytosis or hereditary elliptocytosis, can sometimes present with an elevated MCV if the cells are not uniformly small or if there's a significant reticulocytosis. However, these conditions more commonly present with normocytic or microcytic anemia, and the hematocrit might not be elevated unless there's a significant compensatory response.