4.4 GLUCOSE Flashcards
What is the most frequently performed chemical analysis on urine?
Glucose test
Why is glucose testing included in physical examinations and health screening programs?
To detect and monitor diabetes mellitus and because many cases remain undiagnosed without testing.
What is the renal threshold for glucose reabsorption in the blood?
Approximately 160 to 180 mg/dL.
When is the most informative time to collect urine specimens for glucose testing?
After fasting or 2 hours after meals
What condition occurs during pregnancy due to placental hormones blocking insulin action?
Gestational diabetes
What complications can arise for the baby from gestational diabetes?
Macrosomia, obesity, and increased risk of type 2 diabetes later in life.
Name a condition where glucose appears in urine without hyperglycemia.
Renal glycosuria
What enzyme-based method is used in reagent strips for glucose testing?
Glucose oxidase method
What are the two steps in the glucose oxidase reaction for urine testing?
- Glucose reacts with oxygen to form gluconic acid and hydrogen peroxide.
- Hydrogen peroxide reacts with chromogen to produce a colored compound.
Name two chromogens used in glucose reagent strips.
Potassium iodide (Multistix) and tetramethylbenzidine (Chemstrip).
What can cause a false-positive reaction in glucose oxidase testing?
Contamination by oxidizing agents or detergents
What substances can interfere with the enzymatic reaction, causing false-negative results?
Ascorbic acid,
high levels of ketones,
high specific gravity, l
ow temperature, and
unpreserved specimens.
What is the principle of the Clinitest method for glucose detection?
Reduction of copper sulfate to cuprous oxide in the presence of heat and alkali
What phenomenon can occur at high glucose levels during the Clinitest reaction?
“Pass through” phenomenon
What is the clinical significance of galactose in urine?
It indicates galactosemia, an inborn error of metabolism caused by a deficiency of galactose-1-phosphate uridyl transferase (GALT).
Why is the Clinitest no longer recommended for newborn screening of galactosemia?
Because blood screening for GALT activity is more sensitive and specific.
What reducing sugars other than glucose can cause positive results in the Clinitest?
Galactose, lactose, fructose, maltose, and pentose.
What type of sugar is sucrose, and does it react with Clinitest or glucose oxidase strips?
Sucrose is a non-reducing sugar and does not react with these tests.
What precautions should be taken during the Clinitest procedure due to heat?
Use thick glass test tubes and avoid touching the bottom of the test tube
What percentage of diabetes mellitus cases worldwide are undiagnosed?
Over 50%
How can patients monitor their glucose levels at home?
Using reagent strip methods for blood and urine glucose testing
What happens when blood glucose exceeds the renal threshold?
Glucose appears in urine (glycosuria).
Why might a first-morning urine specimen not represent a fasting state for glucose testing?
Residual glucose from an evening meal may remain in the bladder overnight
What conditions unrelated to diabetes can cause hyperglycemia and glycosuria?
Pancreatitis,
acromegaly,
Cushing syndrome,
hyperthyroidism,
pheochromocytoma,
thyrotoxicosis, and
severe stress.
