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Glucose, Fasting, Plasma / Serum

Item Value
Approval req'd? No
Available Stat? Yes
Test code FBS
Test group Glucose
Performed by Parnassus, Mission Bay & Mt. Zion Chemistry
In House Availability Test available 24 hours per day 7 days per week
Method Oxygen consumption (O2 electrode with glucose oxidase)
Patient Preparation Patients should have fasted (no caloric intake) for a minimum of 8 hours before testing.
Container type Lt Green top preferred, Gold top and Gray top acceptable.
Amount to Collect 1 mL blood Click here for Microdetermination info
Sample type Plasma or serum
Preferred volume 0.5 mL plasma or serum
Min. Volume 0.2 mL plasma or serum
Click here for Microdetermination info
Units mg/dL
Normal range
Normal 70-99 mg/dL
Impaired fasting glucose ("pre-diabetes") 100-125 mg/dL
Diabetes mellitus > 125 mg/dL
Critical value
Neonates < 30 mg/dL or > 170 mg/dL
≥ 1 month old < 50 mg/dL or > 500 mg/dL
Synonyms Diabetes mellitus; FBS; fasting blood sugar
Stability Room temperature 8 hours, refrigerated 2 days
Additional information To convert mg/dl to mmol/L (SI units) multiply by 0.0555.

The stated reference ranges reflect criteria for the diagnosis of diabetes mellitus established by the American Diabetes Association (Diabetes Care, Volume 34, Supplement 1, January 2011). . All recommendations of the ADA are based upon plasma or serum levels). The diagnosis of diabetes mellitus should NOT be made until one of these abnormalities has been confirmed on a subsequent day. Impaired glucose tolerance/impaired fasting glucose implies an increased risk of future diabetes. Fasting levels < 50 mg/dL are frequently found in apparently normal individuals after 1-3 days of fasting, especially in women and children; levels as low as 20 mg/dL may be normal in prematures (Pediatrics 1990;85:834).

Note that fasting whole blood glucose concentrations are approximately 12-15% lower than plasma glucose concentrations and that many point of care whole blood glucose monitors automatically convert results to plasma values. Whole blood glucose results can be manually converted to plasma values by multiplying whole blood results by 1.12, based on the assumption that the sample hematocrit is 45%. Note also that glucose concentrations in capillary blood are higher than those in venous blood. In fasting samples, the differences are small (2 to 5 mg/dL), however, in non-fasting samples, differences as high as 70 mg/dL may be observed.
CPT coding 82947
LOINC code 1558-6
Last Updated 6/20/2016 12:43:46 PM
Entry Number 425
Lab Procedure Link Click here for Procedure
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