Abstract
Hypovolemia and reduced blood sodium levels have been reported in some athletes. Sweat sodium concentration has been shown to be directly proportional to percent plasma volume loss and, therefore, may serve as useful proxy indicator of hypovolemia. This case, a 44-year old male physician with ten years of experience in long distance triathlons and endurance racing, reports himself to be a salty, heavy sweater; has noted significant weight loss during some competitions; and, occasionally, encounters symptoms that could be attributed to hypovolemia, despite drinking to thirst. This case relates his attempts to measure sweat sodium concentration using regional patches and two tools, the Horiba LAQUA twin B-721 Compact Salt Meter and the AquaChek strip (from the swimming pool industry) as compared to a pilocarpine test using a standard approved by the Cystic Fibrosis Foundation. Both tools yielded comparable results, with wide variation in sweat sodium concentration across the samples. The AquaChek showed a consistent bias of -4.16 sodium mEq/L compared to the Horiba. Both are comparable to a pilocarpine standard and validity and reliability of each method was robust when later tested against standard saline solutions. In this case, ease of application, sufficient sweat volume, and potentially reduced contamination from body hair suggest this site for further evaluation of sweat sodium in the field. Additionally, compared to laboratory testing, each method is cost efficient.
Highlights
Hypovolemia and a reduction in blood sodium levels, even to the point of hyponatremia, have been reported in some athletes who lose large volumes of sweat, such as ultra-endurance athletes, football players, and athletes with cystic fibrosis [1,2,3,4,5,6,7,8]
The amount of sodium in human sweat varies widely within and across individuals [9], and, even though the spot ion concentration is consistent over time in acclimated individuals, that concentration has been demonstrated to be directly proportional to percent plasma volume loss, it may serve as useful proxy indicator of hypovolemia [10,11]
While the need for electrolyte replacement continues to be debated, it is the consensus that, for athletes with salt wasting diseases such as cystic fibrosis (CF), salt replacement is necessary to prevent and attenuate ongoing plasma volume contraction and hyponatremia under conditions likely to result in elevated sweat sodium losses [8]
Summary
Hypovolemia and a reduction in blood sodium levels, even to the point of hyponatremia, have been reported in some athletes who lose large volumes of sweat, such as ultra-endurance athletes, football players, and athletes with cystic fibrosis [1,2,3,4,5,6,7,8]. While the need for electrolyte replacement continues to be debated, it is the consensus that, for athletes with salt wasting diseases such as cystic fibrosis (CF), salt replacement is necessary to prevent and attenuate ongoing plasma volume contraction and hyponatremia under conditions likely to result in elevated sweat sodium losses [8]. This case study reports on the attempts of one ultra-endurance athlete to measure his own sweat sodium concentration from regional patch samples using the Horiba LAQUA twinB-721 Compact Salt Meter and the AquaChek test strips during routine training sessions.
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