**Question:** MCHC is increased in

A. Anaemia
B. Polycythemia
C. Thrombocythemia
D. Leukocytosis

**Core Concept:** Mean Corpuscular Hemoglobin Concentration (MCHC) is a laboratory parameter that represents the average concentration of hemoglobin within red blood cells (RBCs). It is calculated as the quotient of mean corpuscular hemoglobin (MCH) divided by mean corpuscular volume (MCV). MCHC is influenced by the concentration of hemoglobin within RBCs and is directly proportional to it.

**Why the Correct Answer is Right:** MCHC is increased in Polycythemia (Option B) because in this condition, there is an increase in the total number of RBCs and hemoglobin concentration within RBCs. This results in a higher MCHC value, indicating increased hemoglobin concentration within RBCs.

**Why Each Wrong Option is Incorrect:**

A. Anaemia (Option A): Although MCHC is indirectly related to RBCs, a decrease in RBCs leads to a decrease in MCHC value. In anaemia, the number of RBCs and/or hemoglobin concentration within RBCs is decreased, causing a lower MCHC value.

C. Thrombocythemia (Option C): Though there may be an increase in platelet count, MCHC is primarily influenced by RBCs and their hemoglobin concentration. Therefore, a normal or decreased MCHC value is expected in thrombocythemia.

D. Leukocytosis (Option D): Leukocytosis refers to an increased number of white blood cells (WBCs). MCHC is influenced by RBCs and their hemoglobin concentration. An increase in WBCs does not directly affect MCHC value, leading to the incorrect choice as a correct answer.

**Clinical Pearl:** In clinical practice, MCHC is used as a screening tool to detect various types of anemias, including microcytic, normocytic, and macrocytic anemias. By assessing MCHC, clinicians can differentiate between these subtypes of anemia, guiding appropriate diagnostic and therapeutic interventions.