Chapter 6 Chemical Examination of Urine Flashcards
What are the four ways results can be reported on reagent strips?
(1) In concentration (mg/dL)
(2) As small, moderate, or large
(3) Using the plus system (1+, 2+, etc.)
(4) As positive, negative, or normal
What is an advantage of the reagent strip being read by an automated instrument?
The consistency in timing and color interpretation regardless of room lighting or testing personnel.
Isothenuria
Excretion of urine that has the same specific gravity (and osmolality) as the plasma. Because the specific gravity of protein-free plasma and the original ultrafiltrate is 1.010, the inability to excrete urine with a higher or lower specific gravity indicates significantly impaired renal tubular function.
Hyposthenuric
Specific gravity less than 1.010.
Hypersthenuric
Specific gravity greater than 1.010.
Reference range of specific gravity
1.002 to 1.035
What is the range of specific gravity that should indicate invalid results.
1.000 or greater than 1.040; physiologically impossible.
What confirmatory method can be used if a sample is found to have a specific gravity of 1.000?
Refractometry
What do specific gravity test strips test for to determine the result? What makes this different from other methods?
The reagent strip specific gravity test does not measure the total solute content but only those solutes that are ionic. Refractometry measures all solute content.
Note: only ionic solutes indicate the renal concentrating and secreting ability of the kidneys and have diagnostic value.
Reference range for urine pH
4.5 to 8.0
What are the three most common reasons for a urine pH to be greater than 8.0?
(1) Improperly preserved and stored
(2) An adulterated specimen (i.e. alkaline agent was previously added)
(3) The patient was given a highly alkaline substance (e.g. medication)
Methodology of pH reagent test strips
Based on a double indicator system using bromthymol blue and methyl red. This indicator combination produces distinctive color change from orange (pH 5.0) to green (pH 7.0) to blue (pH 9.0).
How much protein does normal urine contain?
Up 150mg per day
Where does urine protein originate?
From the ultrafiltration of plasma and from the urinary tract itself.
Uromodulin (Tamm-Horsfall protein)
A mucoprotein synthesized by the distal tubular cells and involved in cast formation.
Urokinase
A fibrinolytic enzyme secreted by tubular cells
Secretory Immunoglobulin
Protein synthesized by renal tubular epithelial cells
Proteinuria
The presence of an increased amount of protein in urine
How does proteinuria occur?
(1) an increase in the quantity of plasma proteins that are filtered
(2) filtering of the normal quantity of proteins but with a reduction in the reabsorptive ability of the renal tubules
What are the four categories of proteinuria?
Prerenal or overflow proteinuria, glomerular proteinuria, tubular proteinuria, and postrenal proteinuria.
Overflow Proteinuria
Results from an increased quantities of plasma proteins in the blood readily passing through the glomerular filtration barriers into the urine.
Glomerular Proteinuria
Occurs in primary glomerular diseases or disorders that cause glomerular damage.
This is a very serious condition; the proteinuria is usually heavy, exceeding 2.5 g/day of total protein and can be as much as 20 g/day.
Postural (orthostatic) Proteinuria
Functional proteinuria; characterized by the urinary excretion of protein only when the individual is in upright (orthostatic) position.
First morning samples will have normal protein content, while throughout the day it’ll be elevated.
Tubular Proteinuria
Occurs when normal tubular reabsorptive function is altered or impaired.
