Correlation of TOSI® Test Soil with Human Blood

Reinfried Früh, Kronberg; Martin Pfeifer, Waldkraiburg; Federal Republic of Germany

Summary

Cleaning protocols of all equipment and detergents used for the cleaning programs must be monitored regularly with suitable controls and shall be optimised whenever needed. A new product shall be optimised already during its development. An efficient way to control the cleaning process is the use of a standardized test soil which can be handled and read out safely by the CSSD personnel without a need for a laboratory or any complex and/or expensive equipment. Furthermore it is mandatory that the test soil correlates in its chemical and physical characteristics with human blood. Blood is known as the most critical contaminant on surgical instruments. An optimisation of a cleaning protocol with unsuitable test soils may bear the risk of limited or even misleading conclusions concerning the achieved cleaning efficiency.

Key words: Cleaning efficiency; Cleaning of surgical instruments; Correlation with blood; Human blood; Test soil; Washer-disinfector

Introduction

Test soils are very important tools in the development process of washers, cleaning detergents and its corresponding washing cycles. During the development of washing machines and washing detergents for the household the performance is regularly tested with textile cloth which are contaminated with typical test soils. Manufacturer of dishwashers use a typicall test soil containing starch for the optimisation of the actual product development.

When reprocessing surgical instruments the cleaning efficiency is normally controlled through the presence or absence of proteins. This may be explained by the fact that human blood is considered to be the most important contaminant on such equipment,

And blood itself mainly consists of proteins. A useful test soil should have the same chemical and physical patterns as human blood.

Problematic nature

Human blood is a very complex composition of a long list of different chemical ingredients, most of them belonging to the group of proteins. The chemical and physical patterns of proteins are characterized by long amino-acid chains with three-dimensional folding, resulting in a complicated property relative to water solubility, decomposition and also denaturation. All these properties are of major importance for the pattern of human blood on surgical equipment.

In addition blood coagulation gets initiated immediately whenever blood gets in contact with any foreign material like an instrument during surgery. This coagulation process will lead to the formation of water insoluble fibrin fibres, which are known to be one of the most resistant compounds on a medical device.

This knowledge makes the need of a test soil visible which must correlate with all the blood specific chemical and physical properties. A simple protein containing test soil will not be able to reflect the complexity of coagulating blood.

It is hard to understand how discussions on the specifications of a suitable test soil can still lead from time to time to recommendations which are unacceptable from a scientific point of view, as the recommended test soils do not meet the requirements described above.

Materials and methods

In order to resolve this problematic nature a test soil was developed and filed for patent application which is based on the coagulation factors fibrin and thrombin. The formation of water insoluble fibrin fibres in a matrix of soluble haemoglobin and albumin has been made feasible through the usage of a “two component system”. The manufacturing process of the test soil therefore reflects the phenomenon of the blood coagulation process.

For testing the characteristics of this standardized test soil in a dipping experiment 20 mg each were plotted on the surface of small stainless steel plates using a robot dosage system. After coagulation the test soil on the test objects was allowed to dry at room temperature (for result refer to Fig. 1). For comparison testing the same type of test objects were contaminated with 75μl each of freshly withdrawn human blood. After coagulation these samples were also allowed to dry at room temperature (see Fig. 2).

	Fig.:2 Test object with human blood
Fig.:1 Test object with standardized test soil

3 different dipping experiments were conducted to compare the dissolution of human blood with the standardized test soil:

1. Characteristics of human blood and test soil in demineralised water at 20°C

This experiment has been set up to control if the soil consists of water soluble or water insoluble or both components. This experiment is put into practice during the very important cold pre-rinsing step of a washer-disinfector.

2. Characteristics of human blood and test soil in demineralised water at 70°C

Proteins denaturate at high temperatures and loose their water solubility. A sophisticated test soil must be able to simulate this important effect.

3. Characteristics of human blood and test soil in a 0.5% alkaline cleaner solution at 70°C

Alkaline cleaners are known for their high cleaning efficiency and are therefore used frequently for reprocessing of medical devices. This favourable cleaning effect must be detected by the test soil.

Results

An evaluation of the dipping experiments was conducted after 5, 10 and 15 minutes respectively and was documented photographically. All trials with human blood and the test soil were conducted in parallel and therefore are comparable directly.

1. Water at 20°C (see Fig. 3a and 3b)

In both experiments the water soluble contents of human blood and the test soil are dissolved quickly while the water insoluble fibrin fibres remain on the test objects. The fibrin fibres of the test soil show a slight brownish colour which results from small amounts of haemoglobin captured by the fibrin fibres.

5 min 10 min 15 min Fig.: 3a Dipping experiment with the test soil in water at 20°C

5 min 10 min 15 min Fig.: 3b Dipping experiment with human blood in water at 20°C

2. Water at 70°C (see Fig. 4a and 4b)

Hot water causes denaturation of proteins in both experiments resulting in no visible cleaning at all. The remaining proteins are hardened and stick on the surface of the test object.

5 min 10 min 15 min Fig.: 4a Dipping experiment with the test soil in water at 70°C

5 min 10 min 15 min Fig.: 4b Dipping experiment with human blood in water at 70°C

3. 0.5% alkaline cleaner solution at 70°C (see Fig. 5a and 5b)

The alkaline cleaner is able to dissolve human blood and the test soil rapidly and completely. The water insoluble fibrin fibres are destroyed by hydrolysis and are dissolved as well.

5 min 10 min 15 min Fig.: 5a Dipping experiment with the test soil in alkaline cleaner at 70°C

5 min 10 min 15 min Fig.: 5b Dipping experiment with human blood in alkaline cleaner at 70°C

Discussion

The test soil did correlate very well with human blood in all dipping experiments. This however is not a big surprise as this test soil contains all relevant blood components. A cleaning protocol which is able to dissolve the water soluble proteins and the water insoluble fibrin of the test soil should be able to clean blood contaminated medical devices with the same efficiency. Only test soils with direct correlation to human blood are meaningful tools to control the cleaning efficiency in the reprocessing of medical devices. Other test soils bear the risk that the cleaning efficiency only gets validated against the said soil but not against praxis relevant blood contaminations.