Why can pancreatitis third-spacing lead to elevated hematocrit?

• A. Hemoconcentration due to dehydration
• B. When fluid leaves the cells, red blood mass stays the same, so false positive of elevated Hct
• C. Bone marrow production of RBCs increases
• D. Plasma volume increases.

Answer: (B)

Pancreatitis can cause fluid to move out of the intravascular space into the interstitial/third spaces, so plasma volume falls. The amount of red blood cells in the blood stays basically the same, so the hematocrit—the proportion of blood that's RBCs—increases. This rise is a concentration effect, not an actual increase in red cell mass, so it can look like a true elevation in hematocrit even though the RBC count hasn’t changed. In other words, it’s a relative increase due to decreased plasma volume, which can be interpreted as a false positive for higher hematocrit.