Accuracy of pH Measurement via pH Paper versus Urine pH Test Strips for Application in Ocular Chemical Injury
DOI:
https://doi.org/10.33192/smj.v78i8.281758Keywords:
Accuracy of pH measurement, ocular chemical injury, chemical eye injury, colorimetric pH test, pH measurement, pH paper, universal indicator paper, urine test strips, urine stripsAbstract
Objective: To evaluate and compare the accuracy of pH paper and urine pH test strips for ocular surface pH assessment in chemical eye injury settings.
Materials and Methods: Nine standard pH solutions (pH 2.00, 4.01, 5.00, 7.00, 8.00, 9.21, 10.00, 11.00, and 12.45) were measured by two observers. Each reference solution was measured 10 times using pH paper and 10 times via urine pH test strips, with each observer conducting five tests per method, resulting in a total of 180 measurements. Accuracy was defined as the percentage of measurements that matched the standard pH value.
Results: All the measurements exhibited good to excellent interobserver and intraobserver reliability. pH paper demonstrated slightly higher accuracy than urine pH test strips (pH paper: 44.4% [95% CI 34.6%–54.7%]; urine pH test strips: 37.8% [95% CI 28.5%–48.1%]). Bland–Altman analysis further indicated superior precision with pH paper measurements than those of the urine pH test strips (95% limits of agreement of -1.6 to +1.8 and -3.0 to +2.8, respectively), particularly at pH extremes outside the range of 5-10.
Conclusion: This study suggests that pH paper provides more accurate and reliable measurements than urine pH test strips across a wider pH range, particularly when analyzing minute fluid volumes like tear samples in cases of ocular chemical injury. Additionally, pH paper's soft texture is not just a matter of convenience but a safety advantage during acute trauma. Therefore, pH paper should be the preferred diagnostic tool for evaluating ocular chemical injury. However, clinical studies are needed to confirm these findings in real-world settings.
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