Glucose, Plasma

CPT: 82947
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Test Details

Synonyms

  • Blood Sugar
  • Fasting Blood Sugar
  • Random Blood Glucose

Use

Diagnose diabetes mellitus; evaluate disorders of carbohydrate metabolism including alcoholism; evaluate acidosis and ketoacidosis; evaluate dehydration, coma, hypoglycemia of insulinoma, neuroglycopenia. A fasting glucose >125 mg/dL on more than one occasion is adequate for the diagnosis of diabetes mellitus. An OGTT is not necessary in this setting. Infants, especially with tremor, cyanosis, convulsions, and respiratory distress should have stat glucose, particularly if there is maternal diabetes, postmaturity, asphyxia, hemolytic disease of the newborn, or possible sepsis. Babies too large or small for gestational age should also have glucose in the first 24 hours of life. Random blood sugars can be used to monitor therapy in diabetics or evaluate presence of insulinoma.1,2

Methodology

Enzymatic

Reference Interval

65−99 mg/dL

Additional Information

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% [approximately 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 iodoacetate (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 eight hours at 25°C and 72 hours at 4°C.

Glucose can be measured in whole blood, serum, or plasma, but plasma is recommended for diagnosis. The molality of glucose (ie, amount of glucose per unit water mass) in whole blood and plasma is identical. Although red blood cells are essentially freely permeable to glucose (glucose is taken up by facilitated transport), the concentration of water (kg/L) in plasma is approximately 11% higher than that of whole blood. Therefore, glucose concentrations in plasma are approximately 11% higher than whole blood if the hematocrit is normal. Glucose concentrations in heparinized plasma are reported to be 5% lower than in serum. The reasons for the latter difference are not apparent, but may be attributable to the shift in fluid from erythrocytes to plasma caused by anticoagulants. The glucose concentrations during an OGTT in capillary blood are significantly higher than those in venous blood [mean of 1.7 mmol/L (30 mg/dL), equivalent to 20% to 25%], but the mean difference in fasting samples is only 0.1 mmol/L (2 mg/dL).

Although methods for glucose analysis exhibit low imprecision at the diagnostic decision limits of 7.0 mmol/L [(126 mg/dL), fasting] and 11.1 mmol/L [(200 mg/dL), postglucose load], the relatively large intraindividual biological variability (CVs of approximately 5% to 7%) may produce classification errors. On the basis of biological variation, glucose analysis should have analytical imprecision <3.4%, bias <2.6%, and total error <8.0%.1,2

Specimen Requirements

Specimen

Plasma

Volume

Entire collection

Minimum Volume

0.5 mL

Container

Gray-top (sodium fluoride) tube

Patient Preparation

Blood should be drawn in the morning after an overnight fast (no caloric intake for at least eight hours), during which time the individual may consume water.

Collection

Label specimen as plasma. Mix well.

Storage Instructions

Maintain specimen at room temperature.

Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Gross hemolysis; improper labeling

Clinical Information

Footnotes

1. Sacks D, Bruns DE, Goldstein DE, et al. Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus. Clin Chem. 2002; 48(3):436-472. 11861436
2. American Diabetes Association. Classification and diagnosis of diabetes. Diabetes Care. 2015 Jan; 38(Suppl 1):S8-S16. 25537714

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
001818 Glucose, Plasma 1558-6 001818 Glucose, Plasma mg/dL 1558-6

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