CLINICAL LAB SCIENEC

CHAPTER 14: CLINICAL CHEMISTRY 381
recommended with each assay batch to monitor procedural para-meters. Use two
controls containing normal and abnormal levels of the enzyme if possible. If r
esults fall outside the acceptable activity limits, check procedural parameters
(i.e., photometer, cuvette, pipettes, tubes, and temperature). If problems persist,
call your technical representative. Please note that some control sera may show
increases of AST activity if activated with pyridoxyl phosphate.
Reporting of Results
Report your findings from the AST/GOT procedure in the form supplied by your
instructor. Activity is expressed in units per liter of specimen (U/L). One unit is defined
as the amount of enzyme that catalyzes the conversion of one micromole of substrate
per minute under specified assay conditions. Data used in factor calculations are
found on the assay sheet provided by the manufacturer. These data are a factor from
the manufacturer of the substrate and are derived from the concentration of the substrate.
The results of the test(s) are calculated by multiplying the absorbance change
for one minute by the calculated factor.
AST/GOT Rate Reaction Calculation
U/L = Delta change per minute × Derived Factor = Value of Unknown in IU/L
An example of calculating AST values is shown in Example 14-1.
Example 14-1
AST/GOT Rate Reaction
0 sec. 15 sec 30 sec 45 sec 60 sec 75 sec 90 sec 105 sec 120 sec
Specimen 1 1.103 1.105 1.110 1.116 1.132 1.148 1.164 1.181 1.199
1. The linear and consistent changes occur from 45 seconds to 105 seconds, for a
minute of activity.
2. The delta change in absorption for a minute is 0.065.
3. Results are calculated by multiplying 0.065 by the derived factor (1768).
4. The calculated results in this example = 115 IU/L.
CHEMISTRY PROCEDURE #5
Electrolytes
Principles
Electrolytes may be referred to as a single entity because four of seven components
are interrelated, and are balanced between the four basic analytes. The tests for
electrolytes refer to positively and negatively charged ions. The positively charged
ions, called cations, are sodium, potassium, calcium, and magnesium; sodium
(Na+) and potassium (K+) are tested for routinely in a set of electrolytes. Negatively
charged ions, called anions, include chloride (Cl – ), bicarbonate (HCO -3 ), and phosphate;
bicarbonate and chloride are the chief electrolytes routinely monitored. Bicarbonate
determinations may be referred to as CO 2
(carbon dioxide) as most of the CO 2
of the body is found in the bicarbonate molecule . In addition, it is simpler to test for
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