Maternal serum alpha-fetoprotein and altitude

Maternal serum alpha-fetoprotein (MS-alpha FP) testing is widely used to sc reen for fetal defects. MS-alpha FP concentrations are affected by a number of variables such as gestational age, maternal weight, number of fetuses, race, and insulin-dependent diabetes. Undefined geographic factors may also influence MS-alpha FP. We have examined the effect of altitude in a sample of 1063 MS-alpha FP results selected to span a range of altitudes. The stu dy sample was subjected to linear regression with and without a term for al titude, and multiple-of-the-median (MoM) values were calculated before and after adjusting for altitude. The median MS-alpha FP was found to decrease an average of 1 ng/mL for every 1100 ft increase in altitude, a change appr oximately equivalent to that seen with an increase in maternal weight of 6 Ib. Adjusting for altitude resulted in the reclassification of 36 of 1063 p atient results (3.4%), although the clinical utility of this adjustment rem ains unexamined. (C) 2000 Harcourt Publishers Ltd.