CLINICAL LAB SCIENEC

382
ESSENTIALS OF CLINICAL LABORATORY SCIENCE
In the Lab
Table 14-1 Normal Values for Serum Electrolytes
Electrolyte
Reference Range mmol/L (mEq/L)
Sodium (Na + ) 135–148
Potassium (K + ) 3.8–5.5
Chloride (Cl – ) 98–108
Bicarbonate (total CO 2
) 22–28
*Actual CO 2
as a gas measurement is seldom done currently. A bicarbonate level provides a useful estimate of the
CO 2
level in the blood.
Extracellular
Space
↑ Sodium
↓ Potassium
↑ Chloride
↑ Bicarbonate
bicarbonate than for CO 2
, as the later is a gas and testing for it requires a great deal
more preparation.
Properly balanced electrolytes are vital for maintaining the narrow range of values
necessary for storage of fluids and proper cellular function and excretion (see
Table 14-1). Electrolyte imbalances are caused by a variety of medical conditions.
Diabetic comas may occur from electrolyte imbalances (a patient rapidly becomes
acidotic, which is a life-threatening condition when the body’s fluids fall outside a slightly
alkaline range of 7.35 to 7.45). Vomiting, diarrhea, and administration of certain medications
may lead to an electrolyte imbalance; such imbalances must be rectified quickly and
thus may require accurate laboratory measurements stat (immediately). Imbalances of
electrolytes often become life-threatening and affect all organs and systems of the body.
Electrolytes may be measured by small portable instruments at the bedside, providing
continual monitoring when necessary. Electrolytes are also included on most
routine biomedical panels of chemistry tests used for screening patients and can be
performed quickly by automated means. Proper flow of
Intracellular
Space
↓ Sodium
↑ Potassium
↓ Chloride
↓ Bicarbonate
FIGURE 14-4 Relative intracellular and extracellular
exchanges of concentration.
Source: Delmar/Cengage Learning.
↓
electrolytes between intracellular spaces and extracellular
spaces must occur to maintain a balance (Figure 14-4).
The methodology for measuring electrolytes has
advanced greatly over the years. Initially, sodium, potassium
and even calcium determinations were performed by
flame photometry, where burning of ions emitted light of
various wavelengths. Chloride was measured by colorimetry
or by the formation of silver chloride when a sample
was introduced to a silver wire. Carbon dioxide was measured
by manometry or colorimetry. Today, most analyzers
use ion-selective electrodes that directly measure these
components. A number of instruments are designed to
measure either plasma, serum, or whole blood, depending
on their operating capacity. Some of these small portable
instruments are adapted for use in physician office laboratories and for point-of-care
testing in the home or the clinic (Figure 14-5).
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