Reaction Rates in Analysis: Test Strips for Urinalysis (OpenStax Chemistry 2e)
Physicians often use disposable test strips to measure the amounts of various substances in a patient’s urine (Figure ). These test strips contain various chemical reagents, embedded in small pads at various locations along the strip, which undergo changes in color upon exposure to sufficient concentrations of specific substances. The usage instructions for test strips often stress that proper read time is critical for optimal results. This emphasis on read time suggests that kinetic aspects of the chemical reactions occurring on the test strip are important considerations.
The test for urinary glucose relies on a two-step process represented by the chemical equations shown here:
The first equation depicts the oxidation of glucose in the urine to yield glucolactone and hydrogen peroxide. The hydrogen peroxide produced subsequently oxidizes colorless iodide ion to yield brown iodine, which may be visually detected. Some strips include an additional substance that reacts with iodine to produce a more distinct color change.
The two test reactions shown above are inherently very slow, but their rates are increased by special enzymes embedded in the test strip pad. This is an example of catalysis, a topic discussed later in this chapter. A typical glucose test strip for use with urine requires approximately 30 seconds for completion of the color-forming reactions. Reading the result too soon might lead one to conclude that the glucose concentration of the urine sample is lower than it actually is (a false-negative result). Waiting too long to assess the color change can lead to a false positive due to the slower (not catalyzed) oxidation of iodide ion by other substances found in urine.
Flowers, P., Theopold, K., Langley, R., & Robinson, W. R. (2019, February 14). Chemistry 2e. Houston, Texas: OpenStax. Access for free at: https://openstax.org/books/chemistry-2e
Date Published: April 7, 2015 Publisher: Public Library of Science Author(s): Takashi Kawahara, Hiroshi Miyamoto, Hiroki Ito, Hideyuki Terao, Hiroji Uemura, Yoshinobu Kubota, Junichi Matsuzaki, Jayoung Kim. http://doi.org/10.1371/journal.pone.0122984 Abstract: Discolored ureteral stents are sometimes encountered in daily clinical practice; however, the mechanism(s) underlying the development of discolored ureteral stents remain unknown. In this study, we … Continue reading
Research Article: Spectral characteristics of urine specimens from healthy human volunteers analyzed using Raman chemometric urinalysis (Rametrix)
Date Published: September 27, 2019 Publisher: Public Library of Science Author(s): Ryan S. Senger, Varun Kavuru, Meaghan Sullivan, Austin Gouldin, Stephanie Lundgren, Kristen Merrifield, Caitlin Steen, Emily Baker, Tommy Vu, Ben Agnor, Gabrielle Martinez, Hana Coogan, William Carswell, Lampros Karageorge, Devasmita Dev, Pang Du, Allan Sklar, Giuseppe Orlando, James Pirkle, John L. Robertson, Benedetta Bussolati. … Continue reading
Research Article: The Post-Resuscitative Urinalysis Associate the Survival of Patients with Non-Traumatic Out-of-Hospital Cardiac Arrest
Date Published: October 4, 2013 Publisher: Public Library of Science Author(s): Chin-Fu Chang, Chao-Jui Li, Chih-Jan Ko, Tsung-Han Teng, Shih-Chang Lai, Mei-Chueh Yang, Chun-Wen Chiu, Chu-Chung Chou, Chih-Yu Chang, Yung-Chiao Yao, Lan-Hsin Wu, Han-Ping Wu, Wen-Liang Chen, Yan-Ren Lin, Pal Bela Szecsi. http://doi.org/10.1371/journal.pone.0075172 Abstract: To analyze whether urine output and urinalysis results are predictive of … Continue reading
Research Article: Identifying and Evaluating Field Indicators of Urogenital Schistosomiasis-Related Morbidity in Preschool-Aged Children
Date Published: March 20, 2015 Publisher: Public Library of Science Author(s): Welcome M. Wami, Norman Nausch, Nicholas Midzi, Reggis Gwisai, Takafira Mduluza, Mark Woolhouse, Francisca Mutapi, Amadou Garba. http://doi.org/10.1371/journal.pntd.0003649 Abstract: BackgroundSeveral studies have been conducted quantifying the impact of schistosome infections on health and development in school-aged children. In contrast, relatively little is known about morbidity … Continue reading