Zentralsterilisation - Ausgabe 4/01
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A.C.P. de Bruijn, T.J.H. Orzechowski, C. Wassenaar:
Validation of the Ninhydrin Swab Test to Monitor Cleaning of Medical Instruments
(Zentr Steril 2001; 9 (4): 235-247)
A number of principles can be applied to evaluate the results of cleaning procedures of reprocessed medical devices. The method most commonly used is visual check after cleaning. A simple swab method may assist in objectifying of the cleanliness. By combining a protein staining agent and a swab method residues of proteinous nature can easily be discovered at low cost. Solid instruments with easily accessible surfaces are clear candidates for this method. Also hollow instruments with an inner diameter of at least 2 mm can be swabbed.
A basic swab procedure is described in the (draft) ISO standard for washer disinfectors using common low-cost, domestic purpose cotton swabs and ninhydrine solution as the staining agent. However, the procedure described has some disadvantages. The test is rather time consuming and unexpected colouring reactions occur that interfere with the reading of the colour reaction on the swab. In order to overcome these problems the critical parameters were identified, such as the type of material used in the swab, the consistency of the material of the swab, the amount of liquid on the swab, incubation temperature and incubation time. The improved protocol renders the method both sensitive (2.5 mg of bovine serum albumin on a glass plate) and reproducible.
Application of a Bioluminescent Method for Checking Cleaning Results
(Zentr Steril 2001; 9 (4): 248-258)
Although infection control demands washing and sterilization of the many instruments that are repeatedly reused in medical procedures, there are no standard methods for evaluating cleaning results nor is much attention paid to validation and documentation of the cleaning process. This report describes a bioluminescent method that uses Luciferase to measure Adenosine Tri-Phosphate (ATP), which is contained in large quantities in human blood, as a marker of residual components after cleaning.
Method: The ATP assay used Lucife-Light Nissui as a reagent and Lumitester K-210 as an analyzer (Nissui Pharmaceuticals Inc., Tokyo, Japan). An ordinary swabbing technique was used to wipe a specified area of the objects of interest and dissolved ATP from the swab tip was analyzed. Initially, the author assessed the linearity and reproducibility of the assay, the stability of ATP before or during the washing process, and the sensitivity of the bioluminescent ATP detection method. Next, the author measured residual ATP on the surface of the surgical instruments used in actual surgical procedures after machine washing.
Results: Assay linearity was quite good for ATP concentration between 2.0 x 10-14 and 2.0 x 10-10 mol/ml (R2 = 0.9988). For the standard ATP solution of 2.0 x 10-13 mol/ml, the mean value and coefficient of variation were 0.96 x 10-13 mol/ml and 9.56, respectively, while for the standard ATP solution of 2.0 x 10-11 mol/ml they were 2.05 x 10-11 mol/ml and 8.63. There was no significant change in the ATP activity for samples left in the post-use condition for 4 weeks prior to cleaning. Furthermore, there was no significant change in the ATP activity due to the heat produced by a washer disinfector. Compared with the Amido Black method, the bioluminescent method had a sensitivity 100 times higher. Residual ATP on the surface of surgical instruments before washing ranged from 9.1 x 10-12 to 1.5 x 10-9 mol. After washing, the residual ATP on almost all scissors and chisels was below the limit of detection. However, residual ATP after the cleaning process was detected on the tips and boxes of needle holders and in the grooves of files.
Conclusions: The results of these tests demonstrate that residual ATP on the surface of surgical instruments after washing could be used as a common scale for evaluating the results of cleaning, and that the bioluminescent method is an excellent technique for measuring ATP concentration in this application.
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