Glucose Test. Information about test and diagnosis of diseases

 Dr. Yousef Al Adbai. 

                 Glucose Test

1. Purpose: Quantitative estimation of glucose in human serum or plasma or Cerebrospinal fluid (CSF) or other body fluids by enzymatic method (GOD-POD). Plasma Glucose determinations are useful in the diagnosis and treatment of diabetes mellitus and in monitoring the response to treatment of diabetes mellitus with insulin or oral hypoglycemic agents. Elevated glucose levels may be associated with pituitary or thyroid dysfunction, renal failure and liver disease, whereas low glucose levels may be associated with insulinoma, hypopituitary neoplasms, or insulin induced hypoglycemia. CSF and fluids have increased glucose in diabetic condition.

2. Principle: Glucose oxidase (GOD) converts glucose to gluconic acid. Hydrogen peroxide formed in this reaction, in the presence of peroxidase (POD), oxidatively couples with 4 - aminoantipyrine (AAP) and phenol to produce red quinone-imine dye. This dye has absorbance maximum at 505 nm. The intensity of color complex is directly proportional to the concentration of glucose in specimen.

3. Performance specifications 

3.1. Linearity: Up to 500 mg/dL of plasma. 

3.2. Measurement range: 40–500 mg/dl

3.3. Sensitivity: The minimum detection limit by this kit is 40 mg/dL

4. Primary sample

4.1. Use only plasma as specimen for the test

4.2. Collect 2 mL of venous blood in a Fluoride—EDTA mixture tube Heparin vacutainer tube.

4.3. Do not use lysed plasma for testing as it may give very high results 

4.4. Do not use contaminated/turbid samples for testing 

Process the sample on the same day within 3 hours of collection.

4.6. Type of container and additive: Fluoride—EDTA mixture tube. 

5. Equipment: Semi-autoanalyzer

6. Reagents: Phosphate buffer; pH 7.5; glucose oxidase; peroxidase; 4 aminoantipyrine; phenol

7. Procedure: 

7.1. Switch on the machine and press “FLUSH “ button by keeping the tubing in a container with 2% detergent for 2 minutes followed by distilled water for 2 minutes

7.2. Press “PROC”. Different test procedures will be displayed. 

7.3. Select the test to be processed by entering its number and then press “ENTER” key.

7.4. Now the assay parameters of the specific test procedure will be displayed. Note down the volume of the reagent and the sample to be used. 

7.5. Feed the blank with each batch and ensure the absorbance of the blank is less than 0.15. If the absorbance of the ‘blank is more than 0.15’ discard the reagent.

7.6. Then feed the test samples and record the values. 

7.7. Check whether the sample is hemolyzed, icteric or lipemic before processing. If the sample is lysed, collect another sample and proceed.

Assay: 

End point 

Reagent volume: 1.0 mL

Wavelength: 505 nm (500–550)

Sample volume: 10 μL

Temperature: 37°C

Zero setting with Reagent blank

Incubation: 5 minutes

8. Interference: Turbid, lipemic, hemolyzed samples, high levels of ascorbic acid, and plasma bilirubin will interfere. Oxalate and fluoride do not interfere.

9. Calculating results:

 10. Biological reference range: 

Glucose Fasting is 60–110 mg/dL. Glucose PP is 90–140 mg/dL Glucose Random is 60–130 mg/dL

11. Critical/Alert level values: 

Below 60 mg/dL 

Above 400 mg/dL

12. Laboratory interpretation: 

Increase of blood glucose usually in diabetes mellitus, decrease in insulinoma. Decrease of CSF sugar in infection. Increase of CSF sugar in hyperglycemia.

13. Potential sources of variability:

13.1. Do not use if the absorbance of the blank reagent is greater than 0.15 at 500 nm as it indicates deterioration of the reagent. 

13.2. Check if the patient has followed the instructions regarding preparation before collecting samples for fasting/post- prandial, plasma glucose/glucose tolerance test.

13.3. The periodic update on the reference ranges needs to be made note of.

BIBLIOGRAPHY

1. Trinder P. Ann Clin Biochem 1969; 6: 24.

Reference➵ Manual of Medical Laboratory Techniques