Hydration

Hydration

Urine Refractometry Standard Operating Procedure

Protocol

Asher Rosinger, axr579@psu.edu

Background Urine specific gravity (USG) is one robust biomarker that has been used previously to assess hydration status; digital, handheld PEN refractometers have been used with much success in a low-resource setting to measure USG. Best, field-friendly method (1,2,3).

Purpose:

  • Procedure for measuring urine specific gravity using a PEN Refractometer
  • Covariates to measure alongside USG: time of urine sample; ambient temperature and humidity, (WBGT preferred); perceived thirst (if possible – how thirsty do you currently feel 0-10); lactation and pregnancy status if female (0 or 1 for both, then number of months lactating, no. of months pregnant).

Equipment:

  1. Gloves
  2. Alcohol prep pads (2/sample)
  3. Batteries, size AAA (4 extra)
  4. PEN Refractometer
  5. Kestrel 5400 heat stress meter (or other
  6. Opaque urine collection cup (1/sample)
  7. Bottled water (1/day)

Protocol:

  1. Each morning, prepare the PEN Refractometer a. Pour room temperature bottled water into an opaque urine cup (wax coated Dixie cup, or similar) b. Measure the temperature of the room using the spirit thermometer, water should be at a similar temperature during measurement and urine collection c. Turn on Refractometer using the ‘START key (1) and immerse the prism head (2) (located within the silver portion of the Refractometer) completely in water within 10 seconds d. The reading should be [0000], if the reading is not [0000], press the “ZERO” key (3)
  1. Ask participant to provide urine sample at the beginning of the interview
  2. Set urine sample aside and conduct interview
  3. Put on gloves
  4. Test urine sample using pregnancy test (see additional SOP for pregnancy testing)
  5. Measure the temperature of the room using the spirit thermometer, record in the data collection app
  6. Press “START”
  7. Place the Refractometer into the opaque cup containing the urine sample as pictured in figure 2 within 10 seconds of powering on
  8. Record the reading of the first measurement as [1.XXXX]
  9. While the PEN Refractometer is in the sample, press “START” again
  10. Record the second reading as [1.XXXX]
  11. Take a third measurement by pressing “START” again
  12. Record the final measurement as [1.XXXX]
  13. After the measurements have been recorded, clean the PEN Refractometer with an alcohol prep pad
  14. Dispose of urine and cups properly

 

Troubleshooting

  1. If an error message displays, there may be too much light interference. In this case, remove the refractometer, press the ‘START’ key again and dip the refractometer into the urine, covering the mouth of the cup with your hand to minimize light interference, this method should give a reading.

References

  1. Rosinger, A. (2015). Heat and hydration status: Predictors of repeated measures of urine specific gravity among Tsimane’ adults in the Bolivian Amazon. American journal of physical anthropology, 158(4), 696-707.
  2. Wutich, A., Rosinger, A. Y., Stoler, J., Jepson, W., & Brewis, A. (2020). Measuring human water needs. American Journal of Human Biology, 32(1), e23350.
  3. Baker, L., Jacobson, H., McGrosky, A., Hinz, E., Wambua, F., Sherwood, A., … & Rosinger, A. Y. (2025). Ambient temperature and wet bulb globe temperature outperform heat index in predicting hydration status and heat perception in a semi-arid environment. Annals of Human Biology, 52(1), 2456152.

To purchase spirit thermometers and PEN refractometers:

  1. Kestrel 5400 heat stress meter: https://kestrelinstruments.com/kestrel-5400-heat-stress-tracker
  2. Atago PEN refractometer: http://www.atago-usa.com/Clinical-Handhelds/PEN-Urine-S-G-p447.html