Hypoglycemia laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Laboratory Findings
Defining Hypoglycemia
Hypoglycemia can't be diagnosed only according to blood glucose level because it is misleading maneuver with high false positive results.The measurement should be repeated using a collection tube that contains an inhibitor of glycolysis and processing should not be delayed.
So, Dependence on three characters to diagnose hypoglycemia is the accepted method. It is called Whipple's triad which includes
- Symptoms of hypoglycemia
- A low plasma glucose concentration corellated with symptoms.
- Correction of glucose level relieves symptoms.
Strategy is to seek Whipple's triad under conditions in which hypoglycemia would be expected:
- If the symptoms occur in the fasting state, that evaluation should be performed during fasting.
- If there is a compelling history of postprandial symptoms, it is reasonable to seek Whipple's triad with frequent, timed plasma glucose measurements and recording of any symptoms after a mixed meal.
- All of the following should be measured:
- Glucose: plasma glucose should be <55 mg/dL.
- Insulin
- C-peptide
- Proinsulin
- Sulfonylurea and meglitinide screen
- Beta-hydroxybutyrate
Fasting evaluation:
- If prolonged fasting may result in an episode of symptomatic hypoglycemia, plasma glucose should be measured repeatedly during fasting.
- If symptoms occur and hypoglycemia is documented, the other tests mentioned above should be performed.
- If the results are equivocal so patient needs another confirmatry test such as the 72-hour fast.
Mixed-meal evaluation:
- If symptoms appear within 5 hours after meals, we should suspect postprandial hypoglycemia.[2]
- Recurrent sampling before and after meals for the following 5 hours will help diagnosis; If severe symptoms occur, the samples for glucose should be analyzed.
- If Whipple's triad is demonstrated, sulfonylureas, meglitinides, and antibodies to insulin should also be measured.
24-hour fasting
- Increased release of glucagon, epinephrine and cortisol is the most important factors that keep blood glucose concentrations from falling during fasting.
- Gluconeogenesis is the most important factor of glucose production after prolonged fast[4].
- If there is high level of insulin, gluconeogenesis will be inhibited causing hypoglycemia during fasting.
The fast is ended when: [1,2]
- 72 hours have passed
- Plasma glucose concentration is ≤45 mg/dL
- Patient has symptoms or signs of hypoglycemia
The precise level of glucose considered low enough to define hypoglycemia is dependent on (1) the measurement method, (2) the age of the person, (3) presence or absence of effects, and (4) the purpose of the definition. While there is no disagreement as to the normal range of blood sugar, debate continues as to what degree of hypoglycemia warrants medical evaluation or treatment, or can cause harm.[1][2][3]
Age Differences
Surveys of healthy children and adults show that plasma glucoses below 60 mg/dL (3.3 mM) or above 100 mg/dL (5.6 mM) are found in less than 5% of samples after an overnight fast.[4] In infants and young children up to 10% have been found to be below 60 mg/dL after an overnight fast. As the duration of fasting is extended, plasma glucose levels can fall further, even in healthy people. In other words, many healthy people can occasionally have glucose levels in the hypoglycemic range without symptoms or disease.
The normal range of newborn blood sugars continues to be debated. Surveys and experience have revealed blood sugars often below 40 mg/dL (2.2 mM), rarely below 30 mg/dL (1.7 mM) in apparently healthy full-term infants on the first day after birth. It has been proposed that newborn brains are able to use alternate fuels when glucose levels are low more readily than adults. Experts continue to debate the significance and risk of such levels, though the trend has been to recommend maintenance of glucose levels above 60-70 mg/dL after the first day after birth. In ill, undersized, or premature newborns, low blood sugars are even more common, but there is a consensus that sugars should be maintained at least above 50 mg/dL (2.8 mM) in such circumstances. Some experts advocate 70 mg/dL as a therapeutic target, especially in circumstances such as hyperinsulinism where alternate fuels may be less available.
References
- ↑ Koh TH, Eyre JA, Aynsley-Green A (1988). "Neonatal hypoglycaemia--the controversy regarding definition". Arch. Dis. Child. 63 (11): 1386–8. PMID 3202648.
- ↑ Cornblath M, Schwartz R, Aynsley-Green A, Lloyd JK (1990). "Hypoglycemia in infancy: the need for a rational definition. A Ciba Foundation discussion meeting". Pediatrics. 85 (5): 834–7. PMID 2330247.
- ↑ Cornblath M, Hawdon JM, Williams AF, Aynsley-Green A, Ward-Platt MP, Schwartz R, Kalhan SC (2000). "Controversies regarding definition of neonatal hypoglycemia: suggested operational thresholds". Pediatrics. 105 (5): 1141–5. PMID 10790476.
- ↑ Samuel Meites, editor-in-chief; contributing editors, Gregory J. Buffone... [et al.] (1989). Pediatric clinical chemistry: reference (normal) values. Washington, D.C: AACC Press. ISBN 0-915274-47-7.