High altitude impact on serum bicarbonate in healthy Mexican children: concerning the overdiagnosis of renal tubular acidosis.

Background: Altitude influences bicarbonate levels, it is a variable that is hardly considered in diagnosing Renal Tubular Acidosis (RTA), so it should be a factor to consider when diagnosing this pathology, especially at 2250 mts over the sea level as it is the case of Mexico City. RTA is most often misdiagnosed. Regarding of this, the present study established reference limits for bicarbonate levels in healthy children without pathologies associated with alterations in the acid-base balance in Mexico City and it´s metropolitan area.

Methods: A total of 267 healthy pediatric patients were included, within normal estimated glomerular filtration rate (eGFR), and without any associated pathology of any alteration in the acid-base balance.

Results: Compared to older children, children younger than two years of age showed statistically higher levels of calcemia and cystatin C. On the other hand, this same group showed lower values of creatininemia, pCO₂, and HCO₃^-. Percentile 50 of bicarbonate in children under two years of age were 19.9 mEq/L and 21.9 mEq/L in those over that age. A correlation was identified between HCO₃^- levels and pCO₂ (r = 0.68; p < 0.001).

Conclusions: In the study population, an effect of altitude on blood levels of pCO₂ and HCO3- was observed.