CLINICAL LAB SCIENEC

210
ESSENTIALS OF CLINICAL LABORATORY SCIENCE
Critical Reminder
Three Basic Types of
Measurements
1. Length or distance
Measured in meters, which may be
divided into units smaller than 1 meter
by the addition of a prefix (Table 9-1).
See Figure 9-1 for a comparison of
the common English system of inches
and a contrasting scale of millimeters.
Figure 9-1 shows a comparison of a
nonmetric or English-style ruler and
the metric scale on the opposite side
of the ruler, which shows that 1 inch
is equal to 2.54 centimeters (cm)
(25.4 millimeters [mm]). Both of these
units of measurement are commonly
used in the clinical laboratory.
2. Weight or mass
Measured in grams (g), which may
be divided into units smaller than 1
gram by the addition of a prefix (Table
9-1). Most electronic scales can be
adjusted to provide measurements
in both ounces (English system) and
grams (metric system). See Figure
9-2 for two types of analytical
laboratory balances used for accurate
measurements in both English and
metric methods.
3. Volume
Measured in liters (L) as the base
unit. Again, a prefix may precede the
base unit to measure units either
smaller or greater than 1 liter, that
is, 1 mL is 1/1,000th of 1 liter.
occur and definitions are modified through nearly international
agreement. Three countries (Myanmar, Liberia, and the US) have
not entirely embraced the new system except for certain areas such
as clinical laboratory science. In the United States, the National
Bureau of Standards sets the official units of measurement by law,
under very strict standards and environmental conditions.
Basic measurements used in the medical laboratory relate to
length, weight (mass), and volume. Measurements used by the
MLT/CLT student will include such measurements as the concentration
of solutions, which includes both weight and volume
measurements. Temperature and units of time in seconds are also
standard measurements used in the laboratory.
The two devices commonly used for measuring length and weight
(mass is similar) are shown in Figures 9-1 and 9-2. The analytical
balances are more commonly used in the clinical laboratory and the
metric ruler would be most often used in the anatomic laboratory.
Elements Used in the Metric System
Length (distance), volume (displacement), and weight (includes
mass, slightly different from weight) are all types of measurements
you will use, as well as time and temperature. The units
of the metric system used for the three basic types of measurement
are meters for length (distance), grams for weight (mass),
and liters for volume (displacement).
Temperature and time are also measurements you will use.
For the most part in the clinical laboratory, temperature is measured
in degrees Celsius (formerly referred to as centigrade), but
sometimes in degrees Kelvin (absolute temperature) for the most
advanced scientific studies.
Various facilities make decisions as to whether a 12-hour or
24-hour time system is to be used. The 24-hour system is most
Table 9-1 Useful Prefixes
The most often used prefi xes in the clinical laboratory when weighing or measuring
volumes:
Prefix Meaning Prefix Meaning
Deca Refers to 10 Deci Refers to one-tenth (0.1)
Hecto Refers to 100 Centi Refers to one-hundredth (0.01)
Kilo Refers to 1,000 Milli Refers to one-thousandth (0.001)
FIGURE 9-1 Comparison of nonmetric (top scale) and metric (bottom scale) rulers.
Source: Delmar/Cengage Learning.
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