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.
What proteins are reabsorbed during tubular proteinuria?
Beta2-microglobulin, retinol-binding protein, alpha2-microglobulin, or lysozyme.
Postrenal Proteinuria
Results from an process anywhere in the urinary tract
An increase in urine proteins are a result of what?
(1) Increased plasma proteins overflowing into the urine (pre-renal)
(2) Renal changes - glomerular tubular, or both
(3) Inflammation and post renal sources
What kind of proteins does SSA precipitation test detect?
All proteins - albumin and globulins
When can an SSA test give a false positive reading?
In the presence of x-ray contrast media and certain drugs (penicillin) in high concentrations
Protein Error of Indicators
A phenomenon characterized by several pH indicators. These pH indicators undergo a color change in the presence of protein despite a constant pH.
Methodology of protein reagent strips
The reaction pad is impregnated with buffer that maintains the test area at pH 3.0. If protein is present, it acts as a hydrogen receptor, accepting hydrogen ions from the pH indicator and there by causing a color change.
The intensity of color is directly proportional to the amount of protein present.
Protein Reagent strips are more sensitive to which protein?
Albumin
What can produce false positive results on a protein reagent strip?
Extremely alkaline (greater than 9.0) or highly buffered
True Hemoglobinuria
Free hemoglobin from plasma passing the glomerular filtration barriers into the ultrafiltrate
Hematuria
An abnormal quantity of red blood cells in the urine
Hemoglobinuria
Urinary presence of hemoglobin
Heme Moiety
A tetrapyrrole ring of a hemoglobin molecule with its centrally bound iron atom.
What is a feature to help differentiate between hematuria and hemoglobinuria?
Urine clarity
Hematuria is often evident by a cloudy or smoky urine; Hemoglobinuria is clear.
What happens to red cells in alkaline pH?
Promotes red blood cell lysis and hemoglobin oxidation.
Hemosiderin
An insoluble form of storage iron. When renal tubular cells reabsorb hemoglobin, the iron is catabolized into ferritin (a major storage form of iron). Ferritin subsequently denatures to form insoluble hemosiderin granules (micelles of ferric hydroxide) that appear in urine 2 to 3 days after hemolytic episode.
Myoglobin
A monomeric heme-containing protein involved in the transport of oxygen to muscles.
Historically, how is hemoglobin and myoglobin differentiated?
Ammonium sulfate precipitation method.
Pseudoperoxidase activity
The action of heme-containing compounds to mimic true peroxidases by catalyzing the oxidation of some substrates in the presence of hydrogen peroxide.
Ascorbic acid interference
Inhibition of a chemical reaction by the presence of ascorbic acid. As a strong reducing agent, ascorbic acid readily reacts with diazonium salts or hydrogen peroxide, removing these chemicals from intended reaction sequences. As a result, colorless dehydroascorbate is formed, causing no color change or a reduced color change.
When can a false-positive result for urinary blood occur?
When menstrual or hemorrhoidal blood contaminates the urine.
An increased number of white cells can indicate what?
Inflammation
When are white blood cells particularly susceptible to lysis?
Hypotonic and alkaline urine, as wells as bacteriauria, high storage temperatures, and centrifugation.
A common cause of leukocyturia
A bacterial infection involving the kidneys (pyelonephritis) or the lower urinary tract, such as cystitis or urethritis.
Advantages of the leukocyte esterase screening test.
(1) To detect the presence of intact and lysed white blood cells
(2) To serve as a screening test for white blood cells that is independent of procedural variations for sediment preparation
What can cause a false-positive leukocyte esterase reading?
Vaginal secretions, drugs, or foodstuffs that color the urine red or pink in acid medium.
What can cause a false-negative leukocyte esterase reading?
Increase protein, increase glucose, and high specific gravity.
Urinary tract infection
The invasion and proliferation of microorganisms in the kidney or urinary tract.
What are the two pathways for the development of a UTI?
(1) The movement of bacteria up the urethra into the bladder (ascending infection)
(2) The movement of bacteria from the bloodstream into the kidneys and urinary tract
Urinary tract infection that involves the bladder
Cystitis
Urinary tract infection that involves the renal pelvis and tubules
Pyelonephritis
Factors that affect nitrite formation and detection
(1) The infecting microbe must be a nitrate reducer
(2) Adequate time must be allowed between voids for bacterial conversion of nitrate to nitrite
(3) Adequate dietary nitrate must be consumed and available for conversion
What can cause false positive results on the nitrite reagent strip?
Highly colored substances that mask results, such as drugs and beet ingestion.
Improper storage with bacterial proliferation.
What can cause false negative nitrite by reagent strip?
Ascorbic acid
What causes glucosuria?
(1) A prerenal condition (hyperglycemia)
(2) A renal condition (defective tubular absorption)
Diabetes Mellitus is the most common disease.
What can cause false-positive results on a glucose reagent strip?
Strong oxidizing reagents, such as bleach, and peroxide contaminants.
What can cause a false-negative result on a glucose reagent strip?
Ascorbic acid and improperly stored specimens.
