4.3 CARBS - LABORATORY METHODS Flashcards
What is the most commonly used specimen for glucose testing?
Serum or plasma
What specimens can be considered for glucose testing
Whole blood,
plasma,
serum,
cerebrospinal fluid,
pleural fluid, and
urine
What is the standard clinical specimen for glucose testing, and which additive is commonly used?
Venous plasma with sodium fluoride as an additive.
What color is the stopper of the tubes containing sodium fluoride for glucose testing?
Gray
What type of blood is used in Point-of-Care Testing (POCT) for glucose levels?
Capillary blood.
By how much is the glucose concentration in whole blood lower than in plasma?
10% - 15% lower.
At what rate is glucose metabolized at room temperature in a blood sample?
7 mg/dL/hour (0.4 mmol/L/hour).
How much does glucose decrease per hour when a blood sample is stored at 4°C?
2 mg/dL/hour (0.1 mmol/L/hour).
What is the conversion factor for glucose from mg/dL to mmol/L?
0.0555.
How long should a serum specimen be separated from the cells to avoid glycolysis according to Henry’s 21st edition?
30 minutes.
How long does sodium fluoride prevent glycolysis in whole blood when refrigerated?
Up to 48 hours.
What is the recommended fasting period for obtaining a fasting blood glucose (FBG) sample?
8 to 10 hours (not longer than 16 hours).
When is fasting plasma glucose (FPG) typically higher, morning or afternoon?
FPG is higher in the morning.
It uses a strip; after capillary puncture, blood flows into the filter paper impregnated with reagent. The strip is then inserted into the glucometer, and the result appears after a few minutes.
glucometer
What can be added to a sample if it is not separated from the cells within 30 minutes?
Sodium fluoride.
How long should a serum specimen be separated from cells according to Bishop?
1 hour.
How long can sodium fluoride prevent glycolysis in whole blood when refrigerated?
Up to 48 hours.
What is the screening test for diabetes mellitus that is taken after at least 8 hours of fasting?
Fasting Blood Sugar (FBS) or Fasting Blood Glucose.
It indicates a prediabetic state and increased risk of developing diabetes, but it is not a clinical entity.
impaired fasting glucose
What type of test uses whole blood in EDTA and provides a picture of a patient’s blood glucose levels over the past three months?
Hemoglobin A1c (HbA1c).
What is the reference range for a normal Hemoglobin A1c (HbA1c) level?
4% - 6% (Henry’s 21st edition).
What HbA1c range indicates an increased risk for diabetes?
5.7% - 6.4%
At what HbA1c level is diabetes diagnosed?
≥ 6.5%.
What test is also known as glycosylated albumin or glycated albumin and monitors glucose control over the previous 3-6 weeks?
Fructosamine test.
What is the reference value for the Fructosamine test?
205 - 285 µmol/L.
What type of glucose test is randomly collected?
Random Blood Sugar (RBS).
In the 2-Hour Post Prandial Blood Sugar (PPBS) test, how much glucose is administered, and when is the sample drawn?
75g of glucose is administered, and the sample is drawn 2 hours after consumption of food
What are the two types of Glucose Tolerance Tests (GTT)?
Oral Glucose Tolerance Test (OGTT) and Intravenous Glucose Tolerance Test (IVGTT).
What type of GTT is performed for patients with malabsorption syndrome who cannot consume the glucose load?
Intravenous Glucose Tolerance Test (IVGTT).
How should a patient prepare for an Oral Glucose Tolerance Test (OGTT)?
The patient should consume 150g of carbohydrates per day for 3 days, discontinue medications affecting glucose tolerance, fast for 8-10 hours, and avoid excessive physical activity.
At what fasting blood glucose (FBG) level should an OGTT be terminated before giving the glucose load?
If FBG is greater than 140 mg/dL.
What is the glucose load for an adult in an OGTT?
75g of glucose dissolved in 300 mL of water.
What glucose dose is given to children in an OGTT?
1.75g of glucose per kilogram of body weight, up to a maximum of 75g.
What is the specimen required for the Hemoglobin A1c (HbA1c) test?
Whole blood in EDTA.
How does Hemoglobin A1c (HbA1c) relate to long-term glucose control?
It monitors long-term diabetes control over the previous 2-3 months.
For every 1% increase in HbA1c, how much does plasma glucose change?
A 1% increase in HbA1c corresponds to a 35 mg/dL (2 mmol/L) change in plasma glucose.
What is the union or reaction involved in Hemoglobin A1c formation?
HbA1c is formed from the reaction between glucose and the hemoglobin protein, specifically the beta chain of hemoglobin.
What is the reference value for Fructosamine?
205-285 µmol/L.
What is the glucose specimen of choice for measuring glucose levels, and what additive is used?
Venous plasma is the standard clinical specimen, with sodium fluoride as the additive (gray stopper tubes).
What is the glucose concentration difference between whole blood and plasma?
Glucose concentration in whole blood is 10%-15% lower than in plasma.
What are the three types of ketones produced by the liver?
Acetone, 2%
acetoacetic acid, 20%
3-β-hydroxybutyric acid 78%
What conditions can lead to increased ketone levels in the body?
Diabetes mellitus,
starvation/fasting,
high-fat diets,
prolonged vomiting,
glycogen storage disease
What specimen types are used to detect ketones?
Fresh serum or urine
hat is the accumulation of ketones in the blood called?
Ketonemia
What is the accumulation of ketones in urine called?
Ketonuria
Which test uses ferric chloride to detect acetoacetic acid and produces a red color?
Gerhardt’s test
Which test uses sodium nitroprusside to detect acetoacetic acid and produces a purple color?
Sodium nitroprusside test
Which enzymatic test detects 3-β-hydroxybutyric acid or acetoacetic acid?
3-hydroxybutyrate dehydrogenase test
What is defined as persistent albuminuria in two out of three urine collections, with values between 30-300 mg/24h?
Microalbuminuria
What ratio establishes clinical proteinuria or macroalbuminuria?
Albumin–creatinine ratio ≥ 300 mg/24 h or ≥ 300 μg/mg creatinine
What collection methods are used for microalbuminuria testing?
Random spot collection, 24-hour collection, timed 4-hour overnight collection
What is the normal fasting plasma glucose (FPG) range in mg/dL?
70-99 mg/dL
What is the normal fasting plasma glucose (FPG) range in mmol/L?
3.9-5.5 mmol/L
What is the impaired fasting glucose (FPG) range in mg/dL?
100-125 mg/dL
What is the impaired fasting glucose (FPG) range in mmol/L?
5.6-6.9 mmol/L
What FPG level in mg/dL indicates a provisional diabetes diagnosis?
≥ 126 mg/dL
What FPG level in mmol/L indicates a provisional diabetes diagnosis?
≥ 7.0 mmol/L
What is the normal two-hour plasma glucose (PG) range in mg/dL?
Answer: ≤ 140 mg/dL
What is the normal two-hour plasma glucose (PG) range in mmol/L?
≤ 7.8 mmol/L
What is the impaired glucose tolerance (IGT) range in mg/dL for a two-hour plasma glucose test?
140-199 mg/dL
What is the impaired glucose tolerance (IGT) range in mmol/L for a two-hour plasma glucose test?
7.8-11.1 mmol/L
What two-hour PG level in mg/dL indicates a provisional diabetes diagnosis?
≥ 200 mg/dL
What two-hour PG level in mmol/L indicates a provisional diabetes diagnosis?
≥ 11.1 mmol/L
methods for glucose determinatio
chemical
-oxidation reduction
-condensation
enzymatic
-glucose dehydrogenase
-glucose oxidase
-hexokinase method
OXIDATION REDUCTION METHODS
Alkaline Copper Reduction Method
Alkaline Ferric Reduction Method (Hagedorn Jensen)
Alkaline Copper Reduction Methods
Folin Wu Method
Nelson Somogyi Method
Neocuprein Method
Benedict’s Method
(Modification of FolinWu)
Alkaline Copper Reduction Method
Principle
Reduction of cupric ions to cuprous ions forming cuprous oxide in hot alkaline solution by glucose.
In the Folin Wu method, what does cuprous oxide react with to produce phosphomolybdenum blue?
Phosphomolybdate
What does cuprous oxide react with in the Nelson-Somogyi method to form arsenomolybdenum blue?
Arsenomolybdate
What reagent is used in the Neocuprein Method to detect glucose, and what color complex is produced?
2,9-Dimethyl-1,10-Phenantroline Hydrochloride; yellow or yellow-orange complex
What is the purpose of Benedict’s Method, and what stabilizing agent does it use?
Detection and quantitation of reducing substances in body fluids; citrate or tartrate as a stabilizing agent
What does copper sulfate react with in Benedict’s Method, and what precipitate is formed?
Glucose under heat; brick red precipitate
What is reduced in the Alkaline Ferric Reduction Method (Hagedorn Jensen) for glucose measurement?
Ferricyanide is reduced to ferrocyanide.
What type of colorimetry is used in the Hagedorn Jensen method, and what is the nature of the end product?
Inverse colorimetry; the end product is colorless.
What is the name of the condensation method used for glucose measurement?
Ortho-toluidine (Dubowski Method)
What is the end product of the Ortho-toluidine (Dubowski Method)?
Green-colored end product
How do we produce the green colored end product in ortho toluidine
Glucose + Aromatic amines (with Glacial Hac and Heat) —> Glycosylamine + Schiff’s base
What enzymes are involved in the Glucose Dehydrogenase method?
Mutarotase, Glucose Dehydrogenase, Diaphorase
What does Mutarotase do in the Glucose Dehydrogenase method?
Converts α-D-glucose to β-D-glucose
What reaction does Glucose Dehydrogenase catalyze in the Glucose Dehydrogenase method?
Converts β-D-glucose + NAD to D-gluconolactone + NADH
What is the role of Diaphorase in the Glucose Dehydrogenase method?
Converts MTT + NADH to MTTH (blue color) + NAD
What is the significance of NADH in the Glucose Dehydrogenase method?
NADH produced is proportional to glucose concentration
Which method for glucose measurement can result in falsely decreased values due to uric acid, bilirubin, and ascorbic acid?
Glucose Oxidase method
What substance can cause falsely increased glucose values in the Glucose Oxidase method?
Bleach
Which chromogens are used in the Colorimetric Glucose Oxidase (Saifer-Gernstenfield) method?
3-methyl-2-benzothiazolinone hydrazone and N,N-dimethylaniline
What does the Polarographic Glucose Oxidase method measure?
The rate of oxygen consumption proportional to glucose concentration
Which glucose measurement method is considered the most specific?
Hexokinase method
What wavelength is used to measure NADPH in the Hexokinase method?
340 nm
