Urinalysis chapter 6

What are some tests that reagent strips can be used for?

• pH

• protein

• glucose

• ketones

• blood

• bilirubin

• urobilinogen

• nitrite

• leukocytes

• specific gravity

What are the two major makers of reagent strips?

• mulitstix

• chemstrip

What is the methodology for using a reagent strip?

Dip strip completely by briefly in specimen, remove excess by running along the edge of the container, blot the strip horizontally on an absorbent medium, wait the specific length of time for reaction and compare against chart in good light

What are some error caused by improper strip technique?

• unmixed specimen (formed elements not detected)

• strip emerged too long (leaching of strip reagents)

• excess urine on strip (runover of reagents)

• no enough time allowed for reaction before reading

• bad lighting

• strip not held close to color chart

• chart from different manufacturer than the strip used

• specimen no allowed to return to room temp after refrigeration

What are reagent strips packaged with?

• opaque containers

• desiccant

What must reagent strips be protected from?

light and moisture

What temperature should reagent strips be stored at?

Below 30 degrees but not refrigerated

What must reagent strips be checked with?

A positive and negative control

When are reagent strip controls run?

• beginning of each shift

• when a new bottle is opened

• when questionable results are obtained

• when the integrity of the strips is in question

Why is distilled water not recommended as a control?

Reagent strip reactions are designed to perform at ionic concentrations similar to urine

Do chemically acceptable reagent strip entirely rule out the possibility of inaccurate results?

No, interfering substances, careless testing and color blindless can still produce errors

What are confirmatory tests?

Procedures that use different reagents or methodologies to detect the same substances as detected by the reagents strips with the same or greater sensitivity or specificity

When are non-reagent strip tests often used?

When questionable results are obtained or highly pigmented specimens are encountered

What two organs are the major regulators of the acid-base content of the body?

lungs and kidneys

How do kidneys help regulate the acid-base balance of the body?

Through the secretion of ammonium ions, hydrogen phosphate and weak organic acids. And through the reabsorption of bicarbonate from the filtrate

Is there a normal value for urinary pH?

No, values must be considered in conjunction with other patient information

What must be taken into account when assessing urine ph?

• acid-base content of blood

• patient renal function

• UTIs

• dietary intake

• age of specimen

What is the alkaline tide?

Increase in urinary ph after meals

What are some causes of acid urine?

• emphysema

• diabetes mellitus

• starvations

• dehydration

• diarrhea

• acid producing bacteria

• high protein diet

• cranberry juice

• medication

What are some causes of alkaline urine?

• hyperventilation

• vomiting

• renal tubular acidosis

• urease producing bacteria

• vegetarian diet

• old specimens

What is the importance of urine ph?

• 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 differentiates respiratory or metabolic acidosis from renal function disorders?

If the acidosis is not related to renal function disorder, the urine is acidic. If it related to renal function, the urine is alkaline

What does precipitation of inorganic chemicals that form urinary crystals and renal calculi depend on?

urine ph

What urine ph typically prevents the formation of calculi?

Alkaline, acidic urine will encourage formation

When is maintaining an acidic urine valuble?

In the treatment of UTIs involving urea-splitting organisms as they do not readily multiple in acidic environments

What is a pH above 8.5 associated with?

An improperly preserved specimen

What is the principle of reagent pH strips?

A double indicator system

• methyl red

• bromothymol blue

What are the range of colors methyl red and bromothymol blue turn in response to pH?

Methyl red: red to yellow, ph 4-6

Bromothymol blue: yellow to blue, 6-9

Are there any know substances that interfere with urine pH measurements?

No

What can interfere with urine pH measurements?

Bacterial growth, cause alkaline shift due to conversion of urea to ammonia

What chemical test is the most indicative of renal disease?

Protein determination

What is often associated with early renal disease?

proteinuria

Does urine normal contain protein?

No, less than 10 mg/dL.

What type of protein is found in urine?

low-molecular weight serum proteins and protein produced in the genitourinary tract

What is the major protein found in urine?

albumin

What happens to the majority of albumin?

Most is not filtered by the glomerulus and what is filtered is reabsorbed by the tubules

What other proteins are found in urine?

• tamm-horsfall protein (THP), also known as uromodulin

• mircoglobulins

What is the clinical significance of proteinuria?

Screening for early signs of renal disease and determining whether proteinuria is normal or pathological in nature.

What are the three major categories of the cause of proteinuria?

• prerenal

• renal

• postrenal

What is prerenal proteinuria caused by?

Conditions that affect the plasma before reaching the kidneys, not indicative of actual renal disease

What is prerenal proteinuria often considered?

A transient condition

What are some causes prerenal proteinuria?

• intravascular hemolysis

• muscle injury

• acute phase reactants (associated with infection and inflammation)

• multiple myeloma

Why is prerenal proteinuria not usually discovered in routine urinalysis?

Reagent strips primarily detect albumin

What is the appearance of bence jones protein associated with?

Multiple myeloma

Most protein in prerenal proteinuria show up in the urine because?

The increased amounts of these proteins exceed the reabsorptive capacity of the renal tubules resulting in overflow

Proteinuria associated with true renal disease may be the result of damage to what parts of the kidneys?

glomerular membrane or the tubules

Some major cause of proteinuria due to presentation of the glomerular membrane with abnormal substances are?

• amyloidosis

• toxic agents

• immune complexes formed in disorders such as lupus

What can override the selective filtration of the glomerulus and cause increased albumin?

Increased blood pressure.

What are some benign causes of renal proteinuria?

• strenuous exercise

• high fever

• dehydration

• cold exposure

What does the detection of microalbuminuria indicate?

Diabetic nephropathy

What is orthostatic (postural) proteinuria?

Persistent benign proteinuria that occurs when the patient is in the vertical position that goes away when a horizontal position is assumed

What are some causes of tubular proteinuria?

• toxic agents/heavy metals

• fanconi syndrome

• severe viral infections

What is the difference in amount of protein between glomerular and tubular proteinuria and why?

Protein levels from glomerular damage are often elevated while in tubular disorders elevation is seldom seen. This is because very little albumin is present in the filtrate to begin with if the glomerulus is undamaged.

What are some causes of postrenal proteinuria?

• bacterial and fungal infections

• injury/trauma

• menstrual contamination

• vaginal secretions

• prostatic fluid/spermatozoa

What is the principle of reagent strip protein tests?

protein error indications

What do protein error indicators produce?

A visible colorimetric reaction in the presence of protein

Why does the indicator in protein reagent strips change color even thought the pH remains constant?

The protein accepts hydrogen ions from the indicator

Why is the test more sensitive to albumin?

It contains more amino groups that other proteins

What reagent do multistix protein strips contain?

tetrabromophenol blue

What reagent do chemstrip protein strips contain?

3',3'',5',5''‑tetrachlorophenol‑3,4,5,6‑tetrabromosulfophthalein

What do both protein reagent strips also contain?

An acid buffer to maintain pH

What is the major source of error with protein reagent strips and what does it cause?

highly buffered alkaline urine, overrides the acid buffer in the strips and causes a false positive

What are some other causes of false positives?

• technical error (leaving strip in specimen too long)

• highly pigmented urine (phenazopyridine)

• contamination with quaternary ammonium compounds, detergents and antiseptics

• high specific gravity

What is the sulfosalicylic acid precipitation test?

A cold precipitation test the reacts equally with all forms of protein

Patients at risk for renal disease can be monitored using random or first morning specimens using semiquantitative methods that measure?

Albumin and creatinine to produce an albumin:creatinine ration

What two reagent strips are available to test albumin and creatinine?

• micral-test

• immunodip

How do micral-test strips test for albumin?

Gold-labeled antihuman albumin antibody-enzyme conjugate. Bound and unbound conjugates move up the strip with the unbound captured in a captive zone containing albumin. The bound albumin moves up the strip and reaches an area with enzyme substrate. The bound reacts and the color change observed

How do immunodip reagent strips test for albumin?

Using immunochromographic technique. Urine enters the container through a vent hole where it encounters blue latex particles coated with antihuman albumin particles. Bound and unbound migrate up strip, unbound particles do not migrate as far a bound. First band is unbound, and second band is bound further up strip. Color intensity of both bands is compared.

What is the advantage of taking a creatinine reading along with albumin?

Comparison of the two can help correct albumin readings for overhydration or dehydration in a random specimen

What is an advantage of the albumin dye binding tests over the regular pad reagent strips?

More specific for albumin

What do albumin dye binding reagent strips use?

DIDNTB (bis(3',3''-diiodo-4',4''-dihydroxy-5',5''-dinitrophenyl)-3,4,5,6-tetrabromosulfonphthalein)

What is the principle for creatinine reagent strips?

pseudo peroxidase activity of copper-creatinine complexes

What is a disadvantage of creatinine strips?

They are unable to detect the absence of creatinine

What causes false negatives in protein reagents strip tests?

• proteins other than albumin

• microalbuminuria

Is a positive creatinine test considered abnormal?

No, creatinine is normally present in urine

What test is the most frequently performed on urine?

glucose

When does glucose begin to appear in the urine?

When the renal threshold has been reached for its active transport

When are the most informative glucose results taken?

Under controlled conditions such as fasting as eating glucose heavy meals can affect results

What are some causes of hyperglycemia that are non-diabetic in orgin?

• pancreatitis

• acromegaly

• Cushing syndrome

• hyperthyroidism

What are some causes of glucosuria that occur without hyperglycemia?

Occur when the reabsorption of glucose by the renal tubules is compromised.

• Fanconi syndrome

• advanced renal disease

• pregnancy

• osteomalica

What is the principle of the glucose test?

Glucose oxidase reaction. Glucose is oxidized to produce gluconic acid and hydrogen peroxide. Peroxide then react with chromogen to produce colored chromogen.

What causes false positive reactions with glucose reagent strips?

Contamination by oxidizing agents and detergents

What chromogen do multistix strips use?

potassium iodide

What chromogen do chemstrips use?

tetramethylbenzidine

What causes false negatives in glucose reagent strips tests?

Substances that interfere with the enzymatic reactions or strong reducing agents

What are some strong reducing agents?

ascorbic acid, prevents the oxidation of chromogen,

What are some other causes of false negatives in glucose reagent strips?

• high levels of ketones

• high specific gravity

• low temp

• improperly preserved specimens

What is the principle of clinitest?

Tests for glucose using the copper reduction method

What can happen with high levels of glucose in the clinitest method?

Pass through where the color passes through the orange/red stage and returns to the low green-brown color

Why must thick-walled tubes used in the clinitest?

Reaction gets very hot

Why can the clinitest not be used as a confirmatory test for glucose?

It’s sensitivity is a minimum of 200 mg/dL

What kind of interference is the clinitest subject to?

From other reducing sugars such as galactose, lactose, fructose, maltose and ascorbic acid

What other sugar is clinically significance in the clinitest?

Galactose

What does the term ketone represent?

The three intermediate products of fat metabolism:

• acetone

• acetoacetic acid

• beta-hydroxybutyrate

Why do ketones not normally appear in the urine?

Metabolized fat is completely broken down

What is testing for ketones in urine most valuable for?

Managing and monitoring type 1 diabetes

What can increased amounts of ketones in the blood lead to?

electrolyte imbalance, dehydration, acidosis and diabetic coma

What else can cause ketonuia?

• Starvation

• cold exposure

• strenuous exercise

• vomiting

• alcoholism

Out of the three ketones which is produced in the largest amount?

beta-hydroxybutyric acid

What is the principle of ketone reagent strips?

the sodium nitroprusside reaction