Spontaneous fluctuations in sweat electrolyte levels were studied in 57 women, including 21 mothers of children with cystic fibrosis (C/F mothers), and in nine men, to determine the effect of the menstrual cycle upon sweat salinity and to see if differences were apparent between C/F heterozygotes and controls. Sweat sodium and chloride concentrations, but not potassium, followed a cyclic pattern in 50% of the premenopausal women. The cyclic fluctuations appeared to follow the known hormonal pattern of the menstrual cycle with both "ovulatory" and "premenstrual" peaks of sweat salinity. Oral administration of a thiazide diuretic prevented or reversed the cyclic rise in sweat salinity, suggesting that the cyclic phenomenon is related to salt and water retention during the menstrual cycle. A single "sweat test" is inadequate for the detection of genetic heterozygotes for cystic fibrosis, because of the variability of sweat salinity. A greater percentage of C/F mothers had occasional sweat chloride determinations above 40 mEq/L than did the controls. Persistently high sweat salinity in an adult may be an indication of the genetic abnormality.
Lieberman J. Cyclic Fluctuation of Sweat Electrolytes in WomenEffect of Polythiazide Upon Sweat Electrolytes. JAMA. 1966;195(8):629–635. doi:10.1001/jama.1966.03100080069018
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