Urine Reagent Strips for Assessing Hypohydration — Do They Work?

Hydrated or not?

Hydration status is an important issue in sports medicine.  Both ends of the spectrum — hypo and hyperhydration — increase risk for morbidity and mortality in the athlete.  As we all know, maintaining euvolemia is an important step in the prevention of heat illness, as the evaporative effect of sweating is one of the body’s mechanisms for heat dissipation.  Conversely, as my colleague and CJSM author Dr. Tamara Hew-Butler has argued on different platforms, a zeal to overhydrate can lead to hyperhydration, hyponatremia, and in extreme cases, death.

There is another way we concern ourselves with hydration status in sports medicine, and that is when assessing athletes who compete in weight classes, or when doing urine drug testing as a screen at a doping control station in competition.  Typically, such assessments are done using different testing modalities on urine specimens.

I am a Medical Delegate for the Federation Internationale de Natation (FINA) and am involved in doping control at long-distance swimming events.  Urine drug screens cannot reliably be done on dilute urine specimens.  In most settings we use refractometry but in some more remote or less developed venues, we may need to use urine reagent strips [WADA has different standards of specific gravity (SG) suitable for urine testing depending on whether refractometry or urine reagent strips are used].

More commonly, here in central Ohio, is the need to assess for hypohydration in the popular sport of wrestling [wrestlers — and other athletes competing in weight classes — will frequently sweat and minimize fluid intake prior to a competitive weigh-in to ‘make weight’ in the class in which they want to compete].  In Ohio high school wrestling, urine reagent strips only are used, and the standard is any sample with SG >1.025 results in a disqualification, with a minimum time period of 48 hours before reassessment.

Having an interest in all these dimensions of testing an athlete’s hydration status, I read with great interest the Brief Report that was published in the November 2019 CJSM: Urine Reagent Strips Are Inaccurate for Assessing Hypohydration: A Brief Report.

Leaders in hydration research — L to R Drs. Martin Schwellnus, Stavros Kavouras, Tamara Hew-Butler, William Roberts

The authors include leaders in the field — Drs. Doug Casa and Stavros Kavouras. The research team noted that in 1999 the NCAA eliminated the use of urine reagent strips in the testing of collegiate wrestlers — it is refractometry only for the collegiate athletes.  They note, conversely, that reagent strips are still used frequently throughout the country at the high school level, varying according to individual state guidelines, according to the National Federation of High School Sports (NFHS).

The team decided to test the accuracy of urine reagent strips at identifying hypohydration using the refractometry as a gold standard by, among other methods, analyzing receiver operator characterstics at both SG 1.020 and 1.025 (reflecting different HS athletic association standards).

This is an elegant study — well designed and with thoughtful statistical analysis.  The beauty of a brief report is that it is, well, brief — I would encourage you to read the study itself.

The team found a relatively acceptable ‘area under the curve’ (AUC) for the strips (AUC 78% for SG 1.025 and AUC 72% for SG 1.020) but a high misclassification rate for urine reagent strips — both failing to identify several individuals who in fact were hypohydrated (presumably allowing them to compete when they shouldn’t) as well as finding some to be hypohydrated when in fact they were euvolemic (preventing them from competing when in fact they should have been allowed).

The authors conclude: “…the urine reagent strips are inaccurate in identifying hyohydration compared with a refractometer….Therefore we suggest that refractometry should be the NCAA and NFHS only choice for measuring …a wrestler’s USG during the weight certification process. (my itals)”

This seems correct. The biggest issue this study leaves me with is a question of cost (and I do not know the answer) — what would it cost an organization like OHSAA and its individual schools to switch from urine reagent strips to refractometry.  Does anyone reading this blog post know the answer to the cost difference between the different methods?

As always here at CJSM we are interested in hearing from you, both if you have an answer to this question, or if you want to give us some feedback about this post, the study, or the journal in general. Please consider commenting below.