Disposables in the Quality Control Laboratory

Nov 02, 2006

Despite their rapid adoption and major contribution to the reduction of operating costs, disposables are misunderstood by many. By their very nature, disposables must be manufactured in a manner that minimizes costs. In theory, at least, disposables should not cost any more than it would to use the corresponding reusable item one time.

This is where the advantages of disposables lie. However, the cost of using an item once cannot be estimated simply by dividing it by the number of expected uses. The cost of recycling, which usually involves cleaning and storing, also must be considered. The requirements for a cleaning validation, storage space and facilities for this recycling will often add a significant cost.

When disposables were introduced to the quality control laboratory, one of the first areas of savings was in cleaning costs. Previously, many large laboratories had full-time dishwashers who worked in a central facility or circulated among specialty laboratories. In organizations too small to gain the efficiency of a dedicated worker, cleaning consumed considerable amounts of employee time; even when the job was assigned to the most junior analyst, the cost of the work, including periodic breakage, was significant.

With some measuring devices, a major cost arose from wear and tear that required periodic recalibration or maintenance activities. Pipettes and syringes wear out through slow chemical corrosion or the mechanical abrasion of surfaces. It is necessary to validate the cleaning procedure and prove that the calibrations are maintained when the items are reused.

False Economy

The need for recalibration or proper maintenance often caused difficulties for people who attempted to reuse disposables. Many laboratories found disposables attractive because of their relatively low initial cost, and then, in a misguided attempt to extend their savings, they tried to reuse items that were really designed for a single use.

In one laboratory, disposable plastic cuvettes were routinely reused by rinsing them with deionized water, followed by an ethanol rinse to help them dry rapidly. The ethanol leached material from the plastic and eventually caused a change in the surface properties of the cuvettes. The result was that the chromophore was adsorbed on the cuvette surface, and then removed during the rinse. The bound chromophore did not have the same absorbance maximum as the chromophore in solution. The net effect was to change the limit of detection for the assay.

The actual effect was to displace the standard curve to the right, along the concentration axis, so that the zero absorbance reading actually occurred at a concentration that was a significant quantity. In this laboratory, the problem was compounded because a standard curve was not used, but the chromophore's extinction coefficient was used to calculate its concentration from a single point reading. A related problem would have arisen if they had run a standard curve, and instructed the software to force the line through zero, as is done in many laboratories.

It is easy to understand why a laboratory trying to save money by reusing disposable cuvettes would also use a single-point assay without a standard curve. In this situation, the problem did not come to light until the changed limit of detection was found during a revalidation of the assay. The revalidation occurred only after an FDA investigator "suggested" that a four-year old assay might be due for a revalidation. As might be expected, the company was trying to save money by minimizing revalidations.

While this may seem to be a minor event, the deliberate reuse of disposables has caused many clinically significant problems. These have ranged from missionary hospitals reusing syringes and needles and contributing to an outbreak of Ebola virus, to US hospitals reusing venous catheters and introducing pyrogens into unsuspecting patients.

Environmental Issues

Environmental issues come in two forms. First there are the problems that arise from the sheer quantity of the material that is being discarded. The use of inexpensive glass items such as pipettes and flint glass test tubes produces material that is easy to recycle and is relatively inert even if not recycled. Also, the production of glass is not really depleting the world of critical material.

Some plastics are very stable and in this respect they resemble glass; the primary problem they create is one of volume in landfills. Most plastics are made from petroleum, but the amount of petroleum consumed for making plastics is relatively small compared with the amount consumed as fuel.

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