Chapter 6: Chemical Examinations

Question 1

Leaving the reagent strip in the urine specimen while recording results of the previous specimen.

Answer 1

Reagents will leach from the strip, causing false-negative results.

Question 2

Failing to remove excess urine while withdrawing the strip from the specimen.

Answer 2

Runover among pads will invalidate results

Question 3

Recording all results immediately after withdrawing the strip from the specimen.

Answer 3

False-negative results (particularly LE) occur because of insufficient reaction time.

Question 4

Using a Chemstrip color chart with a Multistix reagent strip.

Answer 4

Inability to correctly correlate reaction colors is due to differences in reagent strips

Question 5

How will failure to allow a refrigerated specimen to warm to room temperature before testing affect reagent strip testing? Why?

Answer 5

Results will be falsely decreased; enzymatic reactions are temperature-dependent.

Question 6

How are reagent strips protected from deterioration caused by the following?

Answer 6

Moisture: Desiccant in the container and tightly closing the container after removing strips.

Volatile chemicals: Tightly closing containers and avoiding using strips in the presence of fumes.

Light: Opaque containers

Heat: Storing at temperatures below 30°C.

Question 7

What is the significance of the expiration date stamped on reagent strip containers?:

Answer 7

The last date the strips can be guaranteed to produce accurate results.

Question 8

List four situations in which positive and negative controls must be run on reagent strips:

Answer 8

1) At least once every 24 hours.
2) A new bottle is opened.
3) Questionable results are obtained.
4) There is concern over reagent strip integrity.

Question 9

Explain the relationship of urine pH to the formation of crystals and renal calculi:

Answer 9

Urine pH (acid or alkaline) determines the type of crystals and calculi formed.

Question 10

What is the significance of a urine pH of 9?:

Answer 10

The specimen has remained unpreserved at room temperature for too long (a new specimen should be collected).

Question 11

Why do reagent strip pH reactions use both methyl red and bromothymol blue indicators?:

Answer 11

The pH range needed is too broad for one indicator to measure.

Question 12

Describe the unique solubility characteristics of Bence-Jones protein:

Answer 12

Bence-Jones protein precipitates at 40°C to 60°C and dissolves at 100°C.

Question 13

Differentiate between glomerular and tubular proteinuria:

Answer 13

Glomerular proteinuria occurs when protein (primarily albumin) passes through the glomerulus, whereas tubular proteinuria represents defects in the tubular reabsorption of low-molecular-weight proteins usually filtered and reabsorbed.

Question 14

How does detection of microalbuminuria affect patient treatment?:

Answer 14

The patient requires better stabilization of blood glucose levels.

Question 15

Briefly explain the principle of the protein error of indicators. How does highly alkaline urine affect this?:

Answer 15

When the pH remains constant, certain indicators change color in the presence of protein; highly alkaline urine will override the reagent strip pH buffer, thus producing a color change related to pH, instead of protein

Question 16

State a pathologic reason that would cause a negative reagent strip protein reaction and a positive SSA test result:

Answer 16

Multiple myeloma

Question 17

Explain why glycosuria occurs in the presence of hyperglycemia:

Answer 17

Blood glucose levels greater than the renal threshold for glucose produce glucose concentrations in the filtrate that exceed the maximum reabsorptive capacity of the tubules.

Question 18

Explain why the following people would exhibit hyperglycemia and glucosuria:

Answer 18

A person with hyperthyroidism:
the hormone thyroxin opposes the action of insulin by breaking down glycogen to glucose
A person under extreme stress:
epinephrine inhibits insulin secretion.

Question 19

How can glycosuria occur in the absence of hyperglycemia?:

Answer 19

Renal tubular dysfunction

Question 20

Explain the purpose of glucose oxidase and peroxidase in the reagent strip test for glucose:

Answer 20

Glucose oxidase catalyzes a reaction between glucose and room air to form hydrogen peroxide, which is then broken down by peroxidase to produce oxygen that oxidizes a chromogen, producing a color.

Question 21

What is the primary cause of a false-negative test result for glucosuria?:

Answer 21

Old specimens; glycolysis

Question 22

Does the Clinitest detect oxidizing or reducing substances? How does it do this?:

Answer 22

Reducing substances that reduce cupric ions to cuprous ions, releasing oxygen to produce an oxidized colored substance.

Question 23

How will fail to detect “pass-through” effect results?:

Answer 23

A strongly positive result will be reported as negative.

Question 24

What is the primary reason that laboratories perform the Clinitest?:

Answer 24

Screening for galactosemia in children.

Question 25

State two reasons for a positive reagent strip test result for glucose and a negative Clinitest result:

Answer 25

Reagent strips are more sensitive than Clinitest; contamination of containers by strong oxidizing agents.

Question 26

State the three basic reasons for the presence of ketonuria:

Answer 26

Inadequate metabolism or intake of carbohydrates and increased loss of carbohydrate.

Question 27

What is the primary substance detected by sodium nitroprusside? Why is glycine added to the reaction?:

Answer 27

Acetoacetic acid; glycine enhances the detection of acetone.

Question 28

How do the reactions between ketones and interfering substances differ on reagent strips?:

Answer 28

Reaction color from interfering substances fades after standing, whereas color from ketones increases.

Question 29

Why is hemoglobinuria associated with pink plasma and myoglobinuria with normal-colored plasma?:

Answer 29

Myoglobin is more rapidly cleared from the plasma.

Question 30

Why might yellow-brown granules appear in the urine sediment?:

Answer 30

Denaturation of hemoglobin to ferritin by the renal tubular epithelial cells, producing hemosiderin granules.

Question 31

Following precipitation of clear, red urine with ammonium sulfate, what is the significance of a red supernatant?:

Answer 31

Myoglobin is present.

Question 32

What is the purpose of peroxide on a reagent strip pad for blood?:

Answer 32

To detect hemoglobin peroxidase.

Question 33

What is the significance of a speckled reaction on a blood pad?:

Answer 33

Intact RBCsare present.

Question 34

Why are high levels of ascorbic acid of concern with both the glucose and blood reactions?:

Answer 34

Ascorbic acid is a strong reducing agent that can inhibit oxidation of the color-producing chromogens.

Question 35

List in order the three products formed in the degradation of hemoglobin to urobilin:

Answer 35

Unconjugated bilirubin; conjugated bilirubin; urobilinogen.

Question 36

Name two causes of jaundice that produce bilirubinuria and one cause that does not produce:

Answer 36

Bilirubinuria: bile duct obstruction, liver damage

jaundice without bilirubinuria: hemolytic disorders.

Question 37

State two advantages of the Ictotest over the reagent strip bilirubin test:

Answer 37

Ictotest is more sensitive and less affected by interfering substances.

Question 38

What is the major cause of a false-negative test result for bilirubin?:

Answer 38

Old specimens exposed to light

Question 39

Why is it normal to have 0.1 to 1 mg/dL of urobilinogen in the urine?:

Answer 39

A portion of the urobilinogen produced in the intestine is reabsorbed into the blood and passes through the kidneys as it recirculates to the liver.

Question 40

How does hemolytic anemia affect urine urobilinogen? Why? How does biliary obstruction affect urine urobilinogen? Why?:

Answer 40

Hemolytic anemia results in increased bilirubin passing into the intestine; therefore, the production of urobilinogen and its reabsorption into the blood are increased, causing elevated urine levels. The biliary obstruction prevents the passage of bilirubin into the intestine, resulting in no production of urobilinogen to be excreted in the urine.

Question 41

How do the reagent strip reactions for urobilinogen differ between Multistix and Chemstrip?
What other pathologic substance does Multistix detect?:

Answer 41

Multistix uses Ehrlich reagent, which detects urobilinogen, porphobilinogen, sulfonamides, indican, p-aminosalicylic acid, methyldopa, procaine, and chlorpromazine. Chemstrip uses a diazo reaction that is specific for urobilinogen.

Question 42

Describe the diagnostic value of the nitrite test:

Answer 42

Detection of UTI.

Question 43

Why might an automated nitrite reading of positive be changed to negative when the strip is visually examined?:

Answer 43

Automated strip readers may detect an atypical color reaction and provide a positive report.

Question 44

State four reasons why a specimen with a large number of bacteria can have a negative nitrite reaction:

Answer 44

Non-nitrate–reducing bacteria are present; nitrite has been further reduced to nitrogen; lack of dietary nitrate; antibiotic administration; the presence of large amounts of ascorbic acid; high specific gravity.

Question 45

Can a nitrite test be performed on a fresh specimen collected in an unsterile container? Why or why not?

Answer 45

Yes, because if the specimen is fresh, in vitro bacterial multiplication will not have occurred.

Question 46

Why is it possible to have a positive LE reaction and not see any leukocytes in the urine microscopic examination?:

Answer 46

The LE reaction will detect esterase released from lysed leukocytes.

Question 47

When is it possible to have a positive LE test in the absence of bacteria?:

Answer 47

Renal tissue inflammation, fungal and parasitic infections.

Question 48

Why do large quantities of ascorbic acid cause false-negative reactions for bilirubin, urobilinogen by Chemstrip, nitrite, and LE?:

Answer 48

These are diazo reactions,and ascorbic acid will combine with the diazonium salt and prevent the desired reaction.

Question 49

Why does a urine specimen with a low specific gravity produce an alkaline reaction with bromothymol blue in the specific gravity test?:

Answer 49

Hydrogen ions are released from the polyelectrolyte in proportion to specimen concentration.

Question 50

How do specific gravity readings differ between reagent strips and refractometers?:

Answer 50

Reagent strips are not affected by nonionizing high-molecular-weight substances.

Question 51

Explain the need to add 0.005 to the specific gravity readings in urines with a pH of 6.5 or higher:

Answer 51

The alkaline pH of the urine requires additional hydrogen ions to be released from the polyelectrolytes to produce a color change; therefore, the true concentration is not represented.

Question 52

Name three pathologic substances detected by the reagent strip blood reaction. State a reason why each of these appears in the urine.

Answer 52

Substance Reason

a) RBCs: glomerular damage, trauma
b) Hemoglobin: intravascular hemolysis
c) Myoglobin: muscle destruction

Question 53

Indicate the source of the following proteinuria by placing a 1 for prerenal, 2 for renal, or 3 for postrenal in front of the condition: Microalbuminuria

Answer 53

a.__ 2___ Microalbuminuria

Question 54

Indicate the source of the following proteinuria by placing a 1 for prerenal, 2 for renal, or 3 for postrenal in front of the condition: Acute phase reactants

Answer 54

b.__ 1___ Acute phase reactants

Question 55

Indicate the source of the following proteinuria by placing a 1 for prerenal, 2 for renal, or 3 for postrenal in front of the condition.: Pre-eclampsia

Answer 55

c.__ 2___ Pre-eclampsia

Question 56

Indicate the source of the following proteinuria by placing a 1 for prerenal, 2 for renal, or 3 for postrenal in front of the condition. : Vaginal inflammation

Answer 56

d.__ 3___ Vaginal inflammation`

Question 57

Indicate the source of the following proteinuria by placing a 1 for prerenal, 2 for renal, or 3 for postrenal in front of the condition. : Multiple myeloma

Answer 57

e.__ 1___ Multiple myeloma

Question 58

Indicate the source of the following proteinuria by placing a 1 for prerenal, 2 for renal, or 3 for postrenal in front of the condition. : Orthostatic proteinuria

Answer 58

f.__ 2___ Orthostatic proteinuria

Question 59

Indicate the source of the following proteinuria by placing a 1 for prerenal, 2 for renal, or 3 for postrenal in front of the condition.: Prostatitis

Answer 59

g.__ 3___ Prostatitis