CLINICAL LAB SCIENEC

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ESSENTIALS OF CLINICAL LABORATORY SCIENCE
component that may be tested to determine the clearance rate for the kidneys is
that of inulin, a polysaccharide derived from plants. Inulin clearance is used less
frequently than creatinine clearance.
Calculations for Determining the Factor from Data in Table 9-10
U/L = Delta absorbance (Δ) × 1.025 × 1000 = Factor of 4824
8.5 × 0.025 × 1.0
The factor of 4824 is multiplied by the Delta absorbance (Δ) for each unknown value for
the clinical laboratory value for each patient.
For the creatinine clearance test, a 24-hour urine specimen is collected and
stored in a cool environment to retard bacterial growth and alteration of the
urine specimen. Creatinine determinations may be performed on either plasma
or serum samples as well as urine specimens. The calculation of a creatinine clearance
reveals the glomerular flow rate of the kidneys as they remove materials
from the blood. Normal values for creatinine clearance are approximately 110
to 120 mL/min. A factor may be used for surface body area, since the amount
of creatinine removed is proportional to muscle mass. A sample calculation with
arbitrary values is shown here:
Clearance Test for Assessing Kidney Function
Total 24-hour urine volume = 1,650 mL
Minutes (60 minutes × 24 hr)/day = 1,440
Serum creatinine = 2.2 mg/dL
Urinary creatinine = 165 mg/dL
Creatinine clearance =
Urine creatinine × Urine volume (mL)
Serum creatinine × Minutes
Clearance with above data = 165 × 1,650 mL = 85.9 mL/min
2.2 × 1,440 min
Summary
It is important for the clinical laboratory student to have a strong grasp of mathematics,
including knowledge of and calculations using both the English and the
metric systems. Many of the calculations during analysis by instrument will be
performed automatically by computers within the analyzer. However, there are
basic calculations and methods of measurement that will help in troubleshooting
malfunctions of instruments and in analyzing reagents for problems. In some
instances, instrument failure may require that the laboratory worker perform
calculations manually.
When taking licensure and registry boards, mathematic calculations must
be performed to ensure competency in manipulating figures, which indicates an
understanding of the scientific and chemical aspects of the reaction taking place
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