# A spectrophotometric method for determining residual protein levels on reusable surgical instruments: a comparison of six washing methods of instruments with an internal lumen

## TL;DR

This study introduces a new method to test how clean surgical tools with internal channels are after washing, using a protein detection technique.

## Contribution

A new spectrophotometric method using Soiltest® and ninhydrin is validated for evaluating cleanliness of surgical instruments with lumens.

## Key findings

- The Soiltest® method with ninhydrin showed linear quantification (Y=0.2043X–0.03489) and high reproducibility (R²=0.9926).
- Optimal cleaning involved chemical detergents, manual unblocking, and mechanical washing with continuous lumen irrigation.
- The method effectively detects residual proteins to assess cleaning efficacy in complex surgical instruments.

## Abstract

Washing is a multistep process and a critical step in the sterilization of reusable instruments used in surgery. The complexity of the design of some types of instruments, such as those with a lumen, is a major challenge, both in terms of cleaning and of checking their cleanliness.

The aim of this study was to validate a new approach to compare washing methods of reusable instruments with internal lumen. This approach was then tested to compare six methods for washing reamers.

The proposed method was based on detection by Soiltest®, a commercially available soiling test, using ninhydrin in a spectrophotometric approach at 570 nm. To increase the sampling yield of conventional swabbing, we used new wash brushes for each sampling.

Soiltest® results were linearly quantified with a quantitative and reproducible method. The equation of calibration curve was Y=0.2043X–0.03489, the coefficient of determination was 0.9926, and the slope was significantly different from zero (p<0.0001, F-test). The optimal cleaning method for reamers was a combination of chemical detergents, manual cleaning ensuring that no obstruction is present in the instrument, and mechanical washing in a washer-disinfector with a system of continuous irrigation of the lumen of the instrument.

This study validated a new approach to evaluate the cleanliness of critical reusable surgical instruments with lumen based on the detection of protein residues using Soiltest®, by means of a colorimetric method using ninhydrin.