Elevation of which blood value is seen with dehydration, shock, polycythemia vera and infection?

• A. Hematocrit
• B. Hemoglobin
• C. White blood cell count
• D. Platelet count

Answer: (A)

Hematocrit is the proportion of blood that is made up of red blood cells. It rises when either the red cell mass increases or the plasma volume decreases. In dehydration, the body loses fluid from the intravascular space, so plasma volume shrinks while red cells remain, concentrating the blood and increasing hematocrit. In shock, especially when fluid loss is significant (hypovolemic shock), the same hemoconcentration occurs, pushing hematocrit higher. In polycythemia vera, the bone marrow produces more red blood cells, directly increasing the red cell mass and thus the hematocrit. In infection, illness can lead to fever and dehydration or fluid shifts that concentrate the blood, which can also elevate hematocrit. Therefore, hematocrit best fits the pattern described across these conditions, whereas white blood cell count and platelets respond more specifically to infection or inflammatory processes (and may not consistently rise with dehydration or polycythemia vera).