CLINICAL LAB SCIENEC

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ESSENTIALS OF CLINICAL LABORATORY SCIENCE
In the Lab
Reporting of Results
The interpretation of the presence of urinary protein in a turbidimetric specimen is
somewhat subjective. Grade and record the semiquantitative results for the presence
of urinary protein using the scale provided in step #7.
URINALYSIS AND BODY FLUIDS ANALYSIS PROCEDURE #7
Total Protein, Quantitative, for CSF, Urine, and Miscellaneous Body Fluids
Principles
Measurement of urinary proteins is becoming increasingly important in the detection
of renal pathology. Proteinuria (increased amounts of protein in urine) can occur
in increased glomerular permeability, defective tubular reabsorption, and abnormal
secretion of protein into the urinary tract. Albuminuria (increased albumin in urine)
has been implicated as an early indicator of renal damage in diabetes that can be
reversed if identified and treated sufficiently early.
Laboratory personnel should ensure that total protein is confirmed before reporting
a positive total protein, as a positive total protein may lead the physician to order a
needless 24-hour specimen for total protein. Total protein will precipitate and form turbidity
when exposed to SSA or TCA; it will form a blue color when tested similarly with
Coomassie blue instead of SSA or TCA as the reagent. Turbidity may also be measured
for calculation of the total protein by determining absorbance (Abs) using
a spectrophotometer.
Measurement of CSF total protein and specific proteins is used to detect increased
permeability of the blood–brain barrier. The same procedure may be used for measuring
total protein in both CSF and urine. As the color of the urine sample may vary
widely, a urine specimen blank may be used to negate the normal color of the urine.
Proteins in CSF and urine are precipitated in finely dispersed form by TCA. The absorbance
of a sample is read at 420 nm. Protein in blood serum is measured in grams per
deciliter (g/dL), while that of other body fluids is measured in milligrams per deciliter
(mg/dL). The process is otherwise the same.
The following parameters may be used for manual methods or programmed into an
analyzer for automated systems.
Test Parameters (Acceptable Ranges)
Wavelength (TCA method)
340 nm
Wavelength (dye method)
600 nm
Sample/reagent ratio 3:100
Reaction type
Not applicable
End-point equilibration time
5 sec
Reaction direction
Not applicable
Increasing reaction time
5 min
Reaction temperature
Room temperature
Standard
166 mg/dL (may vary by manufacturer)
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