Glucose, Plasma

CPT 82947
Synonyms
  • Blood Sugar
  • Fasting Blood Sugar
  • Random Blood Glucose

Test Details

Use

Diagnose diabetes mellitus; evaluate disorders of carbohydrate metabolism including alcoholism; evaluate acidosis and ketoacidosis; evaluate dehydration, coma, hypoglycemia of insulinoma and neuroglycopenia

Methodology

Enzymatic

References

American Diabetes Association. (2) Classification and diagnosis of diabetes. Diabetes Care. 2015 Jan;38 Suppl:S8-S16.25537714
Sacks D, Bruns DE, Goldstein DE, Maclaren NK, McDonald JM, Parrott M. Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus. Clin Chem. 2002 Mar;48(3):436-472.11861436

Additional Information

According to the ADA, a fasting glucose >125 mg/dL on more than one occasion is adequate for the diagnosis of diabetes mellitus.

The ADA further classifies an intermediate group of individuals whose glucose levels do not meet criteria for diabetes yet are higher than those considered normal. These individuals were defined as having impaired fasting glucose (IFG) in plasma between 100-125 mg/dL.1

The ADA defines three levels of hypoglycemia, with Level 1 cut-point being the most sensitive for detection.2 Level 1 hypoglycemia is defined as a measurable glucose concentration <70 mg/dL but >53 mg/dL. A blood glucose concentration of 70 mg/dL has been recognized as a threshold for neuroendocrine responses to failing glucose in people with diabetes. Because many people with diabetes demonstrate impaired counterregulatory responses to hypoglycemia and/or experience hypoglycemia unawareness, a measured glucose level <70 mg/dL is considered clinically important.

Criteria for diagnosis of diabetes include2:

A1C >6.4% (utilizing NGSP certified and standardized to the DCCT assay);* or

Fasting glucose level >125 mg/dL;* or

A two-hour plasma glucose >199 mg/dL during an OGTT;* or

Classic symptoms of hyperglycemia or hyperglycemic crisis, with random plasma glucose >199 mg/dL.

*In the absence of unequivocal hyperglycemia, criteria 1-3 should be confirmed by repeat testing.

Recent evidence revealed a diurnal variation in FPG, with mean FPG higher in the morning than in the afternoon, indicating that many cases of undiagnosed diabetes would be missed in patients seen in the afternoon. Glucose concentrations decrease ex vivo with time in whole blood because of glycolysis. The rate of glycolysis, reported to average 5% to 7% [~0.6 mmol/L (10 mg/dL)] per hour, varies with the glucose concentration, temperature, white blood cell count and other factors. Glycolysis can be attenuated by inhibition of enolase with sodium fluoride (2.5 mg fluoride/mL of blood) or, less commonly, lithium iodacetate (0.5 mg/mL of blood). These reagents can be used alone or, more commonly, with anticoagulants such as potassium oxalate, EDTA, citrate or lithium heparin. Although fluoride maintains long-term glucose stability, the rate of decline of glucose in the first hour after sample collection in tubes with and without fluoride is virtually identical. (Note that leukocytosis will increase glycolysis even in the presence of fluoride if the white cell count is very high). After four hours, the glucose concentration is stable in whole blood for 72 hours at room temperature in the presence of fluoride. In separated, nonhemolyzed, sterile serum without fluoride, the glucose concentration is stable for 14 days at 25°C and 4°C.

Specimen Requirements

Information on collection, storage, and volume

Specimen

Plasma

Volume

Entire collection

Minimum Volume

0.5 mL (Note: This volume does not allow for repeat testing.)

Container

Gray-top (sodium fluoride) tube or green-top (lithium heparin) tube

Storage Instructions

Maintain specimen at room temperature.

Causes for Rejection

Gross hemolysis; improper labeling; samples unspun or improperly spun (excluding oxalate/NaF)

Collection

Separate plasma within 45 minutes of collection. Only gray-top tubes may be submitted without centrifugation. Label specimen as plasma. Mix well.