Increased mean corpuscular hemoglobin concentration: A case report as an early clue of chronic severe hyponatremia.

rationaleMean corpuscular hemoglobin concentration (MCHC) is a stable parameter, and its true elevation typically indicates hematological disorders. Although occasional reports suggest an association with electrolyte imbalances, the underlying mechanisms remain unclear. PATIENT CONCERNS: An 81-year-old female was admitted with a 3-day history of altered mental status. Complete blood count revealed a markedly elevated MCHC (369 g/L), and peripheral blood smear showed reduced central pallor and mildly hyperchromic erythrocytes, suggestive of cellular dehydration. DIAGNOSES: Chronic severe hypotonic hyponatremia (serum sodium 102 mmol/L), initially alerted by a confirmed "true" MCHC elevation after systematically ruling out common analytical interferences.

interventionsLaboratory personnel issued an early warning for severe electrolyte imbalance prior to biochemical results. The patient subsequently received targeted sodium replacement therapy. OUTCOMES: Following sodium replacement, the patient's serum sodium levels normalized (142 mmol/L), her mental status markedly improved, and her MCHC demonstrated a mirroring downward trend back to normal (337 g/L). LESSONS: Laboratory physicians should consider true MCHC elevation, after excluding interferences, as a potential indicator of chronic hyponatremia. Proactive communication of this finding to clinicians can expedite diagnosis and treatment of critical electrolyte disorders.