CLINICAL LAB SCIENEC

186
ESSENTIALS OF CLINICAL LABORATORY SCIENCE
Introduction
Volumetric containers of varying accuracy and pipettes for transferring
relatively small amounts of liquids are found in the clinical laboratory.
One of the trademarks of laboratories of yesteryear was the presence of a
large amount of glassware and various measuring devices scattered around.
Washrooms were an essential part of the clinical laboratory, and a great
deal of time was spent in washing and ensuring that glassware was chemically
clean. Laboratory assistants and full-time personnel were involved in
washing and drying various pieces of glassware, and even glass pipettes had
their own device for washing and rinsing them for reuse. Today, although
some glassware is used for a few procedures, pipettes are disposable, and
most tubes and containers are made of materials other than glass and are
disposed of after one use.
Initially, specialized pieces of glassware were made individually of
FIGURE 8-1 General measuring blown glass, and there were imperfections in the items as well as variations
in the volumes and the markings on the pieces of equipment. All of
equipment.
Source: Delmar/Cengage the glassware was made from silica, derived from sand. Large quantities
Learning.
of glassware were needed, as most tests were performed individually by
manual methods before the advent of automated analyzers. Cuvettes for
reading specimens in a device called a spectrophotometer were made of high
grade glass. These cuvettes required care in handling to prevent scratching and
had to be scrupulously cleaned between uses. It was only in the past few decades
or so that laboratory pipettes, flasks, beakers, and graduated cylinders began to
be made of plasticized material that gave the appearance of glass but was not
truly “glassware.” Now, plastic can be manufactured that is clear and has few
imperfections that may interfere with the light beamed through the reagent mixture
being read on a spectrophotometer. In today’s laboratory, almost all devices
for measuring and containers for storage are composed of some sort of plastic.
Standardization of Measurement Devices
The National Institute of Standards and Technology (NIST) is the federal technology
agency responsible for developing and promoting accurate measurements
in many disiciplines, including time. The agency provides the standards
and technology necessary to ensure significant accuracy in research and testing,
such as that of the clinical laboratory. Regardless of the design and purpose
of measuring supplies of all sorts, the materials must now meet the specifications
set forth by NIST. Those that meet these standards for accuracy are then
categorized as Class A. Vessels that are used to contain (TC) or to deliver (TD)
are designed to transfer or to store a specified amount (volume). Generally, TC
devices do not deliver exactly the same volume when the solution is transferred
to another container. TD devices, primarily pipettes, indicate that the amount
specified for that item will deliver essentially the same amount.
Glassware that does not meet the Class A specifications recommended by
NIST may have a tolerance range (range within which it is considered accurate)
of more than twice that of an NIST-approved pipette or container. Particularly
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