STRASINGER (7TH ED. | CHAPTER 6: CHEMICAL EXAMINATION OF URINE) Flashcards
What are the (10) parameters that are measured by current commercial reagent strips?
- pH
- Protein
- GLU
- Ketones
- Blood
- Bilirubin
- Urobilinogen
- Nitrite
- Leukocytes
- SG
What are the (2) trade names of the (2) major types of reagent strips?
- Multistix (Siemens Healthcare Diagnostics, Inc., Tarrytown, NY)
- Chemstrip (Roche Diagnostics, Indianapolis, IN)
What are consist of chemical-impregnated absorbent pads attached to a plastic strip?
Chemical reagent strips
When does a color-producing chemical reaction takes place in reagent strips?
When the absorbent pad comes in contact w/ urine
How are the reactions in reagent strips interpreted?
By comparing the color produced on the pad within the required time frame w/ a chart supplied by the manufacturer
What are the (5) semiquantitative values that are used when interpreting reactions in reagent strips?
- Trace
- 1+
- 2+
- 3+
- 4+
True or False
Automated reagent strip readers do not provide Systéme International (SI) units
False, automated reagent strip readers also provide Systéme International (SI) units
What is the methodology / process (/ what are the steps) of reagent strip technique?
- Dip the reagent strip completely, but briefly, into a well-mixed specimen at room temperature
- Remove excess urine from the strip by running the edge of the strip on the container when withdrawing it from the specimen
- Blot the strip horizontally on an absorbent medium
- Wait for the specified length of time for reactions to take place according to the manufacturer
- Compare the colored reactions against the manufacturer’s chart using a good light source
Another process:
1. Dip the reagent strip briefly into a well-mixed uncentrifuged urine specimen at room temperature
2. Remove excess urine by touching the edge of the strip to the container as the strip is withdrawn
3. Blot the edge of the strip on a disposable absorbent pad
4. Wait the specified amount of time for the reaction to occur
5. Compare the color reaction of the strip pads to the manufacturer’s color chart in good lighting
6. Read the results at the correct time, and record the results
What are the (8) errors caused by improper reagent strip technique?
- Formed elements, such as RBCs and WBCs sink to the bottom of the specimen and will be undetected in an unmixed specimen
- Allowing the strip to remain in the urine for an extended period may cause leaching of reagents from the pads
- Allowing excess urine to remain on the strip after its removal from the specimen can produce a runover between chemicals on adjacent pads, producing distortion of the colors
- The timing for reactions to take place varies between tests and manufacturers and ranges from 30 - 120 secs for leukocyte esterase (LE)
- A good light source is essential for accurate interpretation of color reactions
- The strip must be held close to the color chart w/out actually being placed on the chart
- Reagent strips and color charts from different manufacturers are not interchangeable
- Specimens that have been refrigerated must be allowed to return to room temperature before reagent strip testing, as the enzymatic reactions on the strips are temperature dependent
What is the recommended solution to prevent runover between chemicals on adjacent pads in the reagent strip?
Blot the edge of the strip on absorbent paper and hold the strip horizontally while comparing it w/ the color chart
What should be done to obtain best semiquantitative results via reagent strips?
Follow the manufacturer’s stated time
When precise timing of reading results via reagent strips cannot be achieved, what should be done?
The manufacturers recommend that reactions be read between 60 - 120 secs, w/ the LE reaction read at 120 secs
True or False
Manufacturers have a constant direction of the reagent strip to the color chart on the container when reading results
False, manufacturers vary in the direction of the reagent strip to the color chart on the container when reading results
True or False
Automated reagent strip instruments standardize the color interpretation and timing of the reaction and are not subject to room lighting deficiencies or inconsistency among laboratory personnel
True
True or False
The enzymatic reactions on the strips are not dependent to temperature
False, the enzymatic reactions on the strips are temperature dependent
Reagent strips must be protected from deterioration caused by what (4) components?
- Moisture
- Volatile chemicals
- Heat
- Light
How to protect reagent strips from light and moisture?
They are packaged in opaque containers w/ desiccant
When are reagent strips removed from the bottle?
They are removed just before testing and the bottle is tightly resealed immediately
True or False
Bottles (of reagent strips) can be opened in the presence of volatile fumes
False, bottles (of reagent strips) should not be opened in the presence of volatile fumes
What is the storage temperature recommended by manufacturers for reagent strips?
Room temperature below 30°C (but never refrigerated)
All bottles (reagent bottles) are stamped w/ an expiration date, what is the function of this?
This represents the functional life expectancy of the chemical pads
Can reagent strips be used if past the expiration date?
No
Can the chemical pads (in the reagent strips) be touched when removing the strips?
No
What should be done to reagent strips (even if they are still within the expiration date)? What is the purpose of doing this?
Visual inspection should be done each time a strip is used to detect deterioration
How to perform the quality control of reagent strips?
Check w/ both (+) and (-) controls (according to the frequency established by the lab policy)
When do many labs perform QC of reagent strips w/ both (+) and (-) controls?
In the beginning of each shift
What are the (3) situations where QC of reagent strips are done?
- When a new bottle of reagent strips is opened
- When questionable results are obtained
- When there is a concern about the integrity of the strips
What should be done to all QC results?
Must be recorded following lab protocol
Is distilled water recommended as a (-) control for QC of reagent strips? Why or why not?
No, because reagent strip chemical reactions are designed to perform at ionic concentrations similar to urine
What should be the QC results of reagent strips?
All readings of (-) control = (-)
All readings of (+) control = agree w/ published value
What should be done if QC results does not agree w/ published values?
Testing of additional strips and controls
Demonstration of chemically acceptable reagent strips does not entirely rule out the possibility of inaccurate results, what are the other (3) factors that can also produce errors?
- Interfering substances in the urine
- Technical carelessness
- Color blindness
What are the (3) information that the reagent strip manufacturers have published which the lab personnel should be aware of?
-
Limitations
i. Interfering substances of chemical reactions
ii. Sensitivities of chemical reactions
Provide (1) primary example of reagent strip interference
Masking of the color reactions by the orange pigment present in the urine of patients who are taking phenazopyridine compounds
What are procedures using different reagents or methodologies to detect the same substances as detected by the reagent strips with the same or greater sensitivity or specificity?
Confirmatory tests
True or False
Nonreagent strip testing procedures using tablets and liquid chemicals may be available when questionable results are obtained or highly pigmented specimens are encountered. In the past, many of these procedures were used routinely to confirm (+) results
True
The chemical reliability of nonreagent strip testing procedures must be checked using what (2) controls?
- (+) controls
- (-) controls
What are the (10) parameters (reagent strip testing) of chemical examination of urine?
- pH
-
Protein
i. Prerenal proteinuria
ii. Renal proteinuria
a. Microalbuminuria
b. Orthostatic (postural) proteinuria
c. Tubular proteinuria
iii. Postrenal proteinuria - GLU
- Ketones
-
Blood
i. Hematuria
ii. Hemoglobinuria
iii. Myoglobinuria - Bilirubin
- Urobilinogen
- Nitrite
- Leukocyte esterase (LE)
- SG
What are the (2) organs that are the major regulators of the acid-base content in the body?
- Lungs
- Kidneys
How does the lungs and kidneys regulate the acid-base content in the body?
Lungs = secretion of hydrogen (in the form of ammonium ions), hydrogen phosphate, and weak organic acids
Kidneys = reabsorption of bicarbonate (from the filtrate in the convoluted tubules)
What is the pH of the first morning urine of a healthy individual?
Slightly acidic (5.0 - 6.0)
What is the pH of the urine of patients after a meal? What is this phenomena called?
More alkaline pH | alkaline tide
What is the pH of normal random urine?
4.5 - 8.0
What are the pH of the following urine:
- First morning urine (of a healthy individual)
- After a meal (alkaline tide)
- Normal random urine
- 5.0 - 6.0
- More alkaline
- 4.5 - 8.0
What are the (5) information that should be considered in terms of urinary pH?
- Acid-base content of the blood
- Renal function
- Presence of UTI
- Dietary intake
- Age of specimen
What are the (11) causes of acid urine?
- Emphysema
- DM
- Starvation
- Dehydration
- Diarrhea
- Presence of acid-producing bacteria (Escherichia coli)
- High-protein diet
- Cranberry juice
-
Medications
i. Methenamine mandelate (Mandelamine)
ii. Fosfomycin tromethamine (Monurol)
What are the (6) causes of alkaline urine?
- Hyperventilation
- Vomiting
- Renal tubular acidosis (RTA)
- Presence of urease-producing bacteria
- Vegetarian diet
- Old specimens
What are the (2) clinical significance of urinary pH?
- Aid in determining the existence of systemic acid-base disorders of metabolic or respiratory origin
- Management of urinary conditions that require the urine to be maintained at a specific pH
What is the pH of urine in cases of respiratory or metabolic acidosis (which are not related renal function disorders)?
Acidic
What is the pH of urine in cases of respiratory or metabolic alkalosis?
Alkaline
What may be the other conditions of the patient if his/her urinary pH is acidic or alkaline (aside from respiratory or metabolic acidosis and respiratory or metabolic alkalosis, respectively)?
May be a disorder caused by the kidney’s inability to secrete or reabsorb acid or base
What is the cause of formation of urinary crystals and renal calculi?
Precipitation of inorganic chemicals dissolved in the urine
How to prevent the precipitation of inorganic chemicals dissolved in the urine which can lead to urinary crystals and renal calculi? Provide an example
Maintain the urine at a pH that is incompatible with the precipitation of the particular chemicals causing the calculi formation
Example: Calcium oxalate (a frequent constituent of renal calculi) precipitates primarily in acidic and not alkaline urine. Therefore, maintaining urine at an alkaline pH discourages formation of the calculi
What is the importance of urinary pH?
Knowing the pH of urine is important in the identification of crystals
What is an important way in treating UTIs caused by urea-splitting organisms? How? Why?
Maintaining an acidic urine, because they do not multiply as readily in an acidic medium
Because these organisms are responsible for the highly alkaline pH found in specimens that have been allowed to sit unpreserved for extended periods
What are the (2) factors that can control the pH of urine?
- Dietary regulation (primary)
- Medications
What is the difference of pH between individuals on high-protein and high-meat diets vs vegetarians?
High-protein and high-meat diets = acidic urine
Vegetarians = more alkaline urine
Why is the pH of urine of vegetarians more alkaline compared to individuals on high-protein and high-meat diets?
Because after the digestion of many fruits and vegetables, bicarbonate forms
Being a vegetarian causes pH of urine to become more alkaline, however, what is the pH of urine of patients who consume cranberry juice or supplements?
Acidic
What is the use of consuming cranberry juice or supplements? Why?
Home remedy for minor bladder infections, because cranberry juice or supplements inhibit the colonization of certain urinary pathogens
Hence, people who are prone to frequent UTIs are often advised to drink cranberry juice or take over-the-counter cranberry pills
What are the (2) medications prescribed for UTIs? What is the mechanism of these medications?
- Methenamine mandelate (Mandelamine)
- Fosfomycin tromethamine (Monurol)
These medications are metabolized to produce an acidic urine
What is the pH of freshly excreted urine (in normal or abnormal conditions)?
Does not reach above 8.5
What is the clinical significance if the pH of urine is above 8.5? What should be done if the pH of urine is above 8.5?
The specimen is improperly preserved, hence, a fresh specimen should be obtained to ensure the validity of the analysis
What will happen if urine specimens are collected in containers other than single-use laboratory-supplied containers? What is the cause of this urinary pH?
pH of above 8.5, if alkaline detergent remains in the container
Multistix and Chemstrip measure urine pH in what increments?
0.5 - 1-unit increments between pH 5 - 8.5 visually and pH 5 - 9 instrumentally
What is the principle of Multistix and Chemstrip reagent strips for pH? Explain
Double-indicator system (methyl red and bromthymol blue)
Methyl red = red to yellow (pH of 4 - 6)
Bromthymol blue = yellow to blue (pH of 6 - 9)
pH of 5 - 9 = orange (pH 5) to yellow and green to final deep blue (pH 9)
Methyl red + H^+ -> bromthymol blue - H^+
(Red-orange -> yellow) (green -> blue)
What are the substances that interfere with reagent strip reactions for pH?
None
What can cause interference in reagent strip reactions for pH? Why?
Bacterial growth (by certain organisms) which causes marked alkaline shift, usually because of urea conversion to ammonia
What will happen if there is a runover between pH pad and its adjacent pads?
Highly acidic protein (Multistix), as this may produce a reading that is falsely acidic in an alkaline urine
What are the (7) clinical significance of urine pH?
- Respiratory or metabolic acidosis/ketosis
- Respiratory or metabolic alkalosis
- Defects in renal tubular secretion and reabsorption of acids and bases - renal tubular acidosis
Among the routine chemical tests, what is the most indicative of renal disease?
Protein
Often, proteinuria is associated with what?
Early renal disease
What is the important chemical test? Why?
Protein, because proteinuria is indicative of early renal disease
Does a normal urine contain protein? If yes, how much?
Yes, urine contains very little protein, usually < 10 mg/dL or 100 mg per 24 hrs is excreted
Explain the very little amount of protein present in normal urine
Consists primarily of low molecular weight serum proteins that have been filtered by the glomerulus and proteins produced in the genitourinary tract
The very little amount of protein present in normal urine has a low molecular weight, due to this, what is the major serum protein found in normal urine?
Albumin
True or False
Even though albumin is present in high concentrations in the plasma, the normal albumin content in urine is low because majority of albumin presented to the glomerulus is not filtered, and much of the filtered albumin is reabsorbed by the tubules
True
What are the other (5) proteins?
- Small amounts of serum and tubular microglobulins
- Tamm-Horsfall protein (THP)
- Proteins from prostatic secretions
- Proteins from seminal secretions
- Proteins from vaginal secretions
THP is aka what?
Uromodulin
THP is produced by what?
Renal tubular epithelial cells
What is the more recent name for THP?
Uromodulin
What is uromodulin?
Glycoprotein
Uromodulin is produced routinely where?
Ascending loop of Henle
What forms the matrix of casts?
Uromodulin
