Hypoglycemia laboratory findings: Difference between revisions

Jump to navigation Jump to search
Line 64: Line 64:
[[Category:Metabolic disorders]]
[[Category:Metabolic disorders]]
[[Category:Disease]]
[[Category:Disease]]
[[Category:Primary care]]


{{WikiDoc Help Menu}}
{{WikiDoc Help Menu}}
{{WikiDoc Sources}}
{{WikiDoc Sources}}

Revision as of 19:58, 20 May 2013

Hypoglycemia Microchapters

Home

Patient Information

Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Hypoglycemia from other Diseases

Epidemiology and Demographics

Risk Factors

Screening

Natural History, Complications and Prognosis

Diagnosis

Diagnostic criteria

History and Symptoms

Physical Examination

Laboratory Findings

Electrocardiogram

Chest X Ray

CT

MRI

Echocardiography or Ultrasound

Other Imaging Findings

Other Diagnostic Studies

Treatment

Medical Therapy

Surgery

Primary Prevention

Secondary Prevention

Cost-Effectiveness of Therapy

Future or Investigational Therapies

Case Studies

Case #1

Hypoglycemia laboratory findings On the Web

Most recent articles

Most cited articles

Review articles

CME Programs

Powerpoint slides

Images

American Roentgen Ray Society Images of Hypoglycemia laboratory findings

All Images
X-rays
Echo & Ultrasound
CT Images
MRI

Ongoing Trials at Clinical Trials.gov

US National Guidelines Clearinghouse

NICE Guidance

FDA on Hypoglycemia laboratory findings

CDC on Hypoglycemia laboratory findings

Hypoglycemia laboratory findings in the news

Blogs on Hypoglycemia laboratory findings

Directions to Hospitals Treating Hypoglycemia

Risk calculators and risk factors for Hypoglycemia laboratory findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Laboratory Findings

In the majority of children and adults with recurrent, unexplained hypoglycemia, the diagnosis may be determined by obtaining a sample of blood during hypoglycemia. If this critical sample is obtained at the time of hypoglycemia, before it is reversed, it can provide information that would otherwise require a several-thousand-dollar hospital admission and unpleasant starvation testing. Perhaps the most common inadequacy of emergency department care in cases of unexplained hypoglycemia is the failure to obtain at least a basic sample before giving glucose to reverse it.

Defining 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] This article expresses glucose in milligrams per deciliter (mg/dL or mg/100 mL) as is customary in the United States, while millimoles per liter (mmol/L or mM) are the SI (International System) units used in most of the rest of the world. Glucose concentrations expressed as mg/dL can be converted to mmol/L by dividing by 18. For example, a glucose concentration of 90 mg/dL is 5 mmol/L or 5 mM.

Measurement Method

Blood glucose levels discussed in this article are venous plasma or serum levels measured by standard, automated glucose oxidase methods used in medical laboratories. For clinical purposes, plasma and serum levels are similar enough to be interchangeable. Arterial plasma or serum levels are slightly higher than venous levels, and capillary levels are typically in between.[4] This difference between arterial and venous levels is small in the fasting state but is amplified and can be greater than 10% in the postprandial state.[5] On the other hand, whole blood glucose levels (e.g., by fingerprick meters) are about 10%-15% lower than venous plasma levels.[4] Furthermore, available finger stick glucose meters are only warranted to be accurate to within 15% of a simultaneous laboratory value under optimal conditions, and home use in the investigation of hypoglycemia is fraught with misleading low numbers.[6][7] In other words, a meter glucose reading of 39 mg/dL could be properly obtained from a person whose laboratory serum glucose was 53 mg/dL; even wider variations can occur with "real world" home use.

Two other factors significantly affect glucose measurement: hematocrit and delay after phlebotomy. The disparity between venous and whole blood concentrations is greater when the hematocrit is high,[8] as in newborn infants, or adults with polycythemia. High neonatal hematocrits are particularly likely to confound glucose measurement by meter. Second, unless the specimen is drawn into a fluoride tube or processed immediately to separate the serum or plasma from the cells, the measurable glucose will be gradually lowered by in vitro metabolism of the glucose at a rate of approximately 7 mg/dL/hr, or even more in the presence of leukocytosis.[9][10][11]

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.[12] 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.

Presence or Absence of Effects

Research in healthy adults shows that mental efficiency declines slightly but measurably as blood glucose falls below 65 mg/dL (3.6 mM) in many people. Hormonal defense mechanisms (adrenaline and glucagon) are activated as it drops below a threshold level (about 55 mg/dL for most people), producing the typical symptoms of shakiness and dysphoria. On the other hand, obvious impairment does not often occur until the glucose falls below 40 mg/dL, and up to 10% of the population may occasionally have glucose levels below 65 in the morning without apparent effects. Brain effects of hypoglycemia, termed neuroglycopenia, determine whether a given low glucose is a "problem" for that person, and hence some people tend to use the term hypoglycemia only when a moderately low glucose is accompanied by symptoms.

Even this criterion is complicated by the facts that A) hypoglycemic symptoms are vague and can be produced by other conditions; B) people with persistently or recurrently low glucose levels can lose their threshold symptoms so that severe neuroglycopenic impairment can occur without much warning; and C) many of our measurement methods (especially glucose meters) are imprecise at low levels.

Diabetic hypoglycemia represents a special case with respect to the relationship of measured glucose and hypoglycemic symptoms for several reasons. Although home glucose meter readings are sometimes misleading, the probability that a low reading accompanied by symptoms represents real hypoglycemia is higher in a person who takes insulin. Second, the hypoglycemia has a greater chance of progressing to more serious impairment if not treated, compared to most other forms of hypoglycemia that occur in adults. Third, because glucose levels are above normal most of the time in people with diabetes, hypoglycemic symptoms may occur at higher thresholds than in people who are normoglycemic most of the time. For all of these reasons, people with diabetes usually use higher meter glucose thresholds to determine hypoglycemia.

Purpose of Definition

For all of the reasons explained in the above paragraphs, deciding whether a blood glucose in the borderline range of 45-75 mg/dL (2.5-4.2 mM) represents clinically problematic hypoglycemia is not always simple. This leads people to use different "cutoff levels" of glucose in different contexts and for different purposes.

References

  1. Koh TH, Eyre JA, Aynsley-Green A (1988). "Neonatal hypoglycaemia--the controversy regarding definition". Arch. Dis. Child. 63 (11): 1386–8. PMID 3202648.
  2. 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.
  3. 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.
  4. 4.0 4.1 Tustison WA, Bowen AJ, Crampton JH (1966). "Clinical interpretation of plasma glucose values". Diabetes. 15 (11): 775–7. PMID 5924610.
  5. [edited by] John Bernard Henry (1979). Clinical diagnosis and management by laboratory methods. Philadelphia: Saunders. ISBN 0-7216-4639-5.
  6. Clarke WL, Cox D, Gonder-Frederick LA, Carter W, Pohl SL (1987). "Evaluating clinical accuracy of systems for self-monitoring of blood glucose". Diabetes Care. 10 (5): 622–8. PMID 3677983.
  7. Gama R, Anderson NR, Marks V (2000). "'Glucose meter hypoglycaemia': often a non-disease". Ann. Clin. Biochem. 37 ( Pt 5): 731–2. PMID 11026531.
  8. [edited by] John Bernard Henry (1979). Clinical diagnosis and management by laboratory methods. Philadelphia: Saunders. ISBN 0-7216-4639-5.
  9. de Pasqua A, Mattock MB, Phillips R, Keen H (1984). "Errors in blood glucose determination". Lancet. 2 (8412): 1165. PMID 6150231.
  10. Horwitz DL (1989). "Factitious and artifactual hypoglycemia". Endocrinol. Metab. Clin. North Am. 18 (1): 203–10. PMID 2645127.
  11. [edited by] John Bernard Henry (1979). Clinical diagnosis and management by laboratory methods. Philadelphia: Saunders. ISBN 0-7216-4639-5.
  12. 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.


Template:WikiDoc Sources