Most Common Errors When Using Indicator Strips to Monitor Concentrations of Disinfectant Working Solutions

Monitoring the concentration of active substances in working solutions of disinfectants is an important component of effective disinfection measures. Unfortunately, healthcare facility personnel sometimes make a number of errors when storing and using rapid tests, leading to false analysis results. The author hopes this article will be useful for healthcare facility staff and help improve their skills in using rapid tests.

Test strips must be stored and used strictly in accordance with the product instructions. Test strips must not be stored near disinfectants, as chemical vapors from the disinfectant may damage them. Upon first opening the container of test strips, write the opening date on the label. Test strips can be used for three months after the first opening. Do not use expired test strips for analysis.

When performing an analysis, remove only the necessary number of test strips from the case, and do not leave the case open. Avoid touching the indicator zones with your hands. Before analysis, the test strip must not get wet or become contaminated with foreign substances (e.g., fingerprints, grease, etc.).

For analysis, use 50–100 mL of the disinfectant working solution at room temperature. Remove a test strip from the container and immerse it in the working solution for the time specified in the instructions. Then, remove the strip and quickly wipe off excess liquid by dragging the edge of the strip along the rim of the glass. Place the strip on white filter paper, a paper towel, or a gauze pad with the indicator zone facing up. Do not blot the indicator zone with filter paper to remove excess liquid. When performing the test, adhere strictly to the specified immersion time in the working solution and the holding time on the filter paper, as the heterophase chemical reaction requires a specific duration.

Compare the color of the test strip with the reference color scale under normal workplace lighting. Color determination under sodium lamp light may be difficult. The reference scale provided with the test strips should only be used for that specific package. The result is the concentration value corresponding to the closest matching color on the scale. If the color is intermediate, report the corresponding concentration range. Any halos on the test strips not depicted on the reference scale should be disregarded.

Test strips should only be used to monitor the concentrations of disinfectants for which they are intended (or recommended by the manufacturer). For example, “DKhTs” test strips are designed to measure the concentration of working solutions based on dichloroisocyanuric acid (products such as “Brilliant Mig,” “Khlormisept-R,” “Deokhlor” (tablets), “Javel Solid,” “Javel-Kleid,” “Javellion,” “Di-Khlor,” “Klor-Klin,” “Klorsept,” “Purzhavel,” “Sanivap,” “Khlortab”). The concentration of these solutions is determined by active chlorine. Although the concentration of sodium hypochlorite is also measured by active chlorine, “DCICA” test strips must not be used for sodium hypochlorite solutions.

The most common error is performing a single measurement of the active substance concentration in the working solution. To obtain reliable results, three measurements must be taken. The test result is considered valid if at least two of the repeated measurements match. If a retest is necessary, use a fresh portion of the solution.