PubMed · 852115
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H Yatzidis. 1977. An improved biuret reagent.. https://pubmed.ncbi.nlm.nih.gov/852115/
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Regulations recommend the routine application of biochemical tests, such as the Ninhydrin or Biuret tests, to confirm the efficacy of hospital sterile service department (SSD) washer-disinfector cycles in removing proteinaceous material, particularly with respect to prions. The effectiveness of these methods relies on both the effective sampling of the instruments and the sensitivity of the tests employed. Two commercially available contamination assessment tests were evaluated for their sensitivity to ME7 brain homogenate on surgical-grade stainless steel surfaces. Controls were visualized by the application of episcopic differential interference contrast/Epi-fluorecence microscopy (EDIC/EF) combined with the sensitive fluorescent reagent, SYPRO Ruby, which has been shown previously to rapidly visualize and assess low levels of contamination on medical devices. The Ninhydrin test displayed a minimum level of detection observed by 75% of volunteers (MLD(75)) of 9.25 microg [95% confidence interval (95% CI) 8.6-10.0 microg]. The Biuret test provided better sensitivity, with a MLD(75) of 6.7 microg (95% CI 5.4-8.2 microg). However, much lower concentrations of proteinaceous soiling (pg) were visualized using the EDIC/EF microscopy method. From these findings, it is clear that these approved colorimetric tests of cleaning are relatively insensitive. This investigation demonstrates how large amounts (up to 6.5 microg) of proteinaceous brain contamination could remain undetected and the instruments deemed clean using such methods. The application of more sensitive cleanliness evaluation methods should be applied to reduce the risk of iatrogenic transmission of prion disease in 'high-risk' instruments such as neurosurgical devices.
Dextran interference in biuret-type assays of total serum proteins was investigated in a Belgian National External Quality Assurance Survey with 256 participants. In vitro supplementation of therapeutic (10% Gentran 70) dextran concentrations showed a broadly varying (from 0 to 20%) negative interference. The analytical interference was found to depend on both the sodium hydroxide and tartrate concentrations in the reagent formulation. The dry chemistry biuret method was not affected by the dextran interference. In a number of cases, the effects observed may be of clinical importance. Both clinicians and laboratory staff should be aware of the persistence of this analytical problem.
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