Effect of Moderate Altitude Short Stay on Complete Blood Count Parameters

High-altitude habitation is known to impose physiological stress, notably affecting red blood cells and hemoglobin concentration. The effects of moderate altitude exposure on leukocytes and platelets remain less well-characterized. This study aimed to longitudinally evaluate hematological adaptations, focusing on leukocyte and platelet dynamics, in sea-level residents exposed to moderate altitude.

A prospective cohort of 45 healthy male international students from West Africa was followed over six months after their arrival at 2,270 meters above sea level (Southwestern Saudi Arabia). Complete blood count (CBC) was measured within 48 hours of arrival, at two months, and at six months. Longitudinal changes in hematological parameters were assessed using mixed-effects linear regression.

Exposure of healthy sea-level residents to moderate altitude (2,270 m) led to significant hematological adaptation. Hemoglobin, red blood cells (RBC), and hematocrit increased at two and six months (all p < 0.05), while red cell distribution width (RDW-CV) decreased, indicating more uniform erythropoiesis. Mean corpuscular indices (MCV, MCH, MCHC) remained unchanged. Leukocyte counts were overall stable, but neutrophils declined significantly at both time points (p < 0.01). Lymphocytes rose transiently at two months (p = 0.022), and monocytes increased modestly by six months (p = 0.046). Platelet counts did not change significantly, but platelet volume indices (MPV, PDW) rose consistently (p < 0.001), suggesting altered platelet activation.

Moderate altitude exposure triggers increased erythropoiesis, mild neutropenia, and platelet activation without altering platelet count. These changes reflect complex hypoxia-driven mechanisms and highlight the need for altitude-specific CBC reference ranges. Further research is needed to explore their clinical significance.