Clinical Significance of Carbs

What are the normal and critical fasting glucose reference ranges?

• normal: 70-99 mg/dL

• critical: less than 40 mg/dL or greater than 500 mg/dL

CSF glucose reference range

50-80 mg/dL (or 60-70% of plasma glucose)

What are the two test methods used for determining plasma glucose?

• glucose oxidase-peroxidase reaction

• glucose hexokinase

  • most used and most specific

  • possible interference due to hemolysis, lipemia, or certain drugs

Glucose is ___ ___ in whole blood than plasma.

15% lower

Why must blood be centrifuged within one hour of collection when determining glucose levels?

to prevent the cellular components of blood from metabolizing glucose and altering the results

Sodium fluoride (gray top) tubes inhibit ___ in the specimen.

glycolysis

galactosemia

• an inborn error of carbohydrate metabolism

• infant lacks the GALT enzyme leading to a buildup of galactose in circulation

What is used to diagnose hypoglycemia?

• the Wipple’s Triad

  • patient has signs and symptoms

  • testing and documentation of low glucose is performed

  • alleviation of symptoms upon the ingestion of glucose

What drugs can cause hypoglycemia?

alcohol, insulin, and sulfonylureas (for diabetic patients to control blood sugar)

What is fasting hypoglycemia?

• plasma glucose is not maintained between meals due to:

  • liver enzyme deficiencies

  • insulinomas (causes excessive insulin production)

  • severe liver disease

  • severe renal disease (kidneys are excreting too much glucose)

What is reactive hypoglycemia?

• a delayed, exaggerated insulin response

• instead of insulin increasing after eating, insulin spikes hours after

• leads to hypoglycemia

What are the 4 types of diabetes mellitus?

• type 1

• type 2

• gestational

• other/secondary

In all 4 types of diabetes mellitus, clinical presentation includes:

• polyphagia (hunger)

  • the cells cannot metabolize glucose because no insulin present = no glucose in our cells

• polydipsia (thirsty), polyuria, and dehydration

  • the kidneys are trying to excrete excess glucose, causing dehydration

What does uncontrolled diabetes mellitus look like in the lab?

• hyperglycemia

• glucosuria

• electrolyte imbalance

  • decreased blood and urine pH (polyuria causes electrolyte loss)

• increased serum and urine SG

urine microalbumin test

• measures the amount of albumin in the urine, which can indicate early signs of kidney damage in individuals with diabetes

• reference range: < 30 mg / 24 hours

• microalbuminuria: 30 - 300 mg / 24 hours

urine albumin/creatinine ratio

• a comparison of albumin to creatinine in the urine

• creatinine is present in all urine at a reliable rate

• used to assess kidney function and damage in diabetic patients

• helps estimate the degree of albuminuria over a 24-hour period

diabetes insipidus

A disorder characterized by the excretion of large volumes of dilute urine due to a deficiency of antidiuretic hormone (ADH)

can lead to severe dehydration and electrolyte imbalances

diabetes mellitus type 1

• marked by insulinopenia

• autoantibodies attack the beta cells in the pancreas

• hyperglycemia

• sudden weight loss, nausea, blurred vision, confusion, dehydration

What happens during diabetic ketoacidosis (DKA)?

• bloodstream has excess glucose because pancreatic cells are being destroyed (no insulin production)

• the liver creates more glucose because the cells are starving

• the body begins to break down fat for energy and ketones build up

• ketones cause decreased pH leading to metabolic acidosis

• the kidneys use excess water to clear excess glucose and ketones, causing dehydration

diabetes mellitus type 2

• insulin resistance and deficiency

• strong genetic predisposition

• gradual onset

• manageable or even reversible

• hyperglycemia

gestational diabetes

• glucose intolerance during pregnancy due to hormonal or metabolic changes

• usually resolves afterwards

• can lead to increased risk of type 2 diabetes later in life

gestational diabetes can cause (in the baby):

• high birthweight

• increased infant insulin (which can lead to hypoglycemia)

• higher risk of being overweight and developing diabetes later on

Causes of secondary/other diabetes

• pancreatic diseases

• endocrinopathies

• drug or chemical-induced

hemoglobin A1C

• aka glycosylated hemoglobin

• elevated plasma glucose causes hemoglobin to take up glucose

• reported as a percentage

  • provides an average blood sugar level over the past 2-3 months

• less variable than plasma glucose levels

• good indicator of how well a patient is controlling their diabetes

hemoglobin A1C reference ranges

• normal: < 5.7%

• pre-diabetic: 5.7 - 6.4%

• diabetic (well controlled): < 7%

What are two limitations to hemoglobin A1C testing?

• patient has a hemoglobinopathy (such as sickle cell)

• patient has increased RBC turnover

glucose renal threshold

around 180 - 200 mg/dL

What plasma glucose level after performing a 2-hour glucose tolerance test indicates diabetes?

> 200 mg/dL

When is glucose tolerance testing performed on pregnant women?

• if the mother is over 25 years old

• if the pregnancy is deemed high risk

How is glucose tolerance testing done with pregnant women?

• patient is given a 50 g glucose drink

• a specimen is collected 1 hour later

• if results are > 130 mg/dL, the diagnosis phase is performed next

• diagnostic phase

  • patient fasts overnight

  • a fasting specimen is drawn

  • patient drinks a 100 g glucose drink

  • 1 hour, 2 hour, and 3 hour specimens are collected

  • one or more high result is diagnostic for diabetes