CARBOHYDRATES

Carbohydrates

are compounds containing C, H, and O. The general formula for a carbohydrate

is Cx(H2O)y. All carbohydrates contain C=O and -OH

functional groups. There are some derivatives from this

basic formula because carbohydrate derivatives can be formed by the addition of other chemical groups, such as phosphates, sulfates, and amines.

The classification of carbohydrates is based on four different properties: (1) the size of the base carbon chain (2) the location of the CO function group (3) the number of sugar units (4) the stereochemistry of the compound

Classification of Carbohydrates

generic classifications based on the number of carbons in the molecule:

Trioses contain three carbons

Tetroses contain four carbons

Pentoses contain five carbons

Hexoses contain six carbons

Glyceraldehyde the smallest carbohydrate three-carbon compound

Carbohydrates are hydrates of aldehyde or ketone

derivatives based on the location of the CO functional group.

The two forms of carbohydrates: ▪ The Aldose Form▪ has a terminal carbonyl group (O=CH-) called an

aldehyde group

▪ The Ketose Form▪ form has a carbonyl group (O=C) in the middle linked

to two other carbon atoms (called a ketone group).

Several models are used to represent carbohydrates.

The Fisher projection has the aldehyde or ketone at the top of the drawing. The carbons are numbered starting at the aldehyde or

ketone end. The compound can be represented as a straight chain or

might be linked to show a representation of the cyclic, hemiacetal form.

The Haworth projection represents the compound in the cyclic form that is more

representative of the actual structure. This structure is formed when the functional (carbonyl)

group (ketone or aldehyde) reacts with an alcohol group on the same sugar to form a ring called either a hemaketal or hemiacetal ring, respectively.

Monosaccharides, Disaccharides,

and Polysaccharides

Another classification of carbohydrates is based on number of sugar units in the chain: Monosaccharides Disaccharides Oligosaccharides Polysaccharides

This chaining of sugars relies on the formation of glycoside bonds that are bridges of oxygen atoms.

When two carbohydrate molecules join, a water molecule is produced.

When they split, one molecule of water is used to form the individual compounds. This reaction is called hydrolysis.

Monosaccharides are simple sugars that cannot be

hydrolyzed to a simpler form. These sugars can contain three, four,

five, and six or more carbon atoms (known as trioses, tetroses, pentoses, and hexoses, respectively).

The most common include glucose, fructose, and galactose.

Disaccharides are formed when two monosaccharide units

are joined by a glycosidic linkage. On hydrolysis, disaccharides will be split into

two monosaccharides by disaccharide enzymes (e.g., lactase) located on the microvilli of the intestine. These monosaccharides are then actively absorbed.

The most common disaccharides are maltose (comprising 2--D-glucose molecules in a 1→ 4 linkage), lactose, and sucrose.

Oligosaccharides are the chaining of 2 to 10 sugar units

Polysaccharides are formed by the linkage of many monosaccharide units. more than 10 monosaccharides. Amylase hydrolyzes starch to disaccharides in the duodenum. The most common polysaccharides are starch (glucose molecules)

and glycogen. STARCH

▪ Primary CHO in the diet and is found in most plants GLYCOGEN

▪ Storage form of carbohydrates▪ Formed from glucose by the liver

CELLULOSE▪ Another polysaccharide in plants▪ Not digested by humans, it does provide bulk for proper intestinal functioning

Glucose Metabolism

Glucose is a primary source of energy for humans.

The nervous system, including the brain, totally depends on glucose from the surrounding extracellular fluid (ECF) for energy.

Nervous tissue cannot concentrate or store carbohydrates; therefore, it is critical to maintain a steady supply of glucose to the tissue. For this reason, the concentration of glucose in the ECF must be maintained in a narrow range.

When the concentration falls below a certain level, the nervous tissue loses the primary energy source and are incapable of maintaining normal function.

Fate of Glucose

Most of our ingested carbohydrates are polymers, such as starch and glycogen.

Salivary amylase and pancreatic amylase are responsible for the digestion of these

non-absorbable polymers to dextrins and disaccharides

Maltase an enzyme released by the intestinal

mucosa Hydrolyze disaccharides to

monosaccharides Sucrase

Hydrolyzes sucrose to glucose and fructose

Lactase Hydrolyzes to glucose and galactose

When disaccharides are converted to monosaccharides, they are absorbed by the gut and transported to the liver by the hepatic portal venous blood supply.

Glucose is the only carbohydrate to be directly used for energy or stored as glycogen. Galactose and fructose must be converted

to glucose before they can be used.

After glucose enters the cell, it is quickly shunted into one of three possible metabolic pathways, depending on the availability of substrates or the nutritional status of the cell.

The ultimate goal of the cell is to convert glucose to carbon dioxide and water. During this process, the cell obtains the high-energy molecule adenosine triphosphate (ATP) from inorganic phosphate and adenosine diphosphate (ADP).

Gluconeogenesis The conversion of amino acids by the

liver and other specialized tissue, such as the kidney, to substrates that can be converted to glucose.

also encompasses the conversion of glycerol, lactate, and pyruvate to glucose.

Glycogenesis When the cell’s energy requirements are being met,

glucose can be stored as glycogen. Glucose-6-phosphate is converted to glucose- 1-

phosphate, which is then converted to uridine diphosphoglucose and then to glycogen by glycogen synthase.

Several tissues are capable of the synthesis of glycogen, especially the liver and muscles.

Hepatocytes are capable of releasing glucose from glycogen or other sources to maintain the blood glucose concentration. This is because the liver synthesizes the enzyme glucose-6-phosphatase.

Glycogenolysis is the process by which glycogen is

converted back to glucose 6-phosphate for entry into the glycolytic pathway.

Regulation of Carbohydrate Metabolism

The liver, pancreas, and other endocrine glands are all involved in controlling the blood glucose concentrations within a narrow range.

During a brief fast, glucose is supplied to the ECF from the liver through glycogenolysis.

When the fasting period is longer than 1 day, glucose is synthesized from other sources through gluconeogenesis.

Hormones Produced By The Pancreas:

1. Insulin is the primary hormone responsible for the entry of

glucose into the cell. synthesized by the cells of islets of Langerhans in the

pancreas. The release of insulin causes an increased movement of

glucose into the cells and increased glucose metabolism. It decreases plasma glucose levels by increasing the

transport entry of glucose in muscle and adipose tissue by way of nonspecific receptors.

It also regulates glucose by increasing glycogenesis, lipogenesis, and glycolysis and inhibiting glycogenolysis.

Insulin is the only hormone that decreases glucose levels and can be referred to as a hypoglycemic agent

2. Glucagon is the primary hormone responsible for increasing

glucose levels. It is synthesized by the cells of islets of

Langerhans in the pancreas and released during stress and fasting states.

When these cells detect a decrease in body glucose, they release glucagon.

Glucagon acts by increasing plasma glucose levels by glycogenolysis in the liver and an increase in gluconeogenesis.

It can be referred to as a hyperglycemic agent (

Hormones Produced By The Adrenal Gland:

1. Epinephrine produced by the adrenal medulla increases plasma glucose by inhibiting insulin secretion,

increasing glycogenolysis, and promoting lipolysis. is released during times of stress

2. Glucocorticoids primarily cortisol Are released from the adrenal cortex on stimulation by

adrenocorticotropic hormone (ACTH). Cortisol increases plasma glucose by decreasing intestinal

entry into the cell and increasing gluconeogenesis, liver glycogen, and lipolysis.

Hormones Produced By The Anterior Pituitary Glands:

1. Growth hormone increases plasma glucose by decreasing the entry of

glucose into the cells and increasing glycolysis. Its release from the pituitary is stimulated by

decreased glucose levels and inhibited by increased glucose.

2. ACTH Decreased levels of cortisol stimulate the anterior

pituitary to release ACTH. ACTH, in turn, stimulates the adrenal cortex to

release cortisol and increases plasma glucose levels by converting liver glycogen to glucose and promoting gluconeogenesis.

Two other hormones affect glucose levels:

Thyroxine The thyroid gland is stimulated by the production of

thyroid-stimulating hormone (TSH) to release thyroxine that increases plasma glucose levels by increasing glycogenolysis, gluconeogenesis, and intestinal absorption of glucose.

Somatostatin Produced by the cells of the islets of Langerhans of

the pancreas, increases plasma glucose levels by the inhibition of insulin, glucagon, growth hormone, and other endocrine hormones.

HYPERGLYCEMIA

is an increase in plasma glucose levels. In healthy patients, during a

hyperglycemia state, insulin is secreted by the cells of the pancreatic islets of Langerhans.

Insulin enhances membrane permeability to cells in the liver, muscle, and adipose tissue. It also alters the glucose metabolic pathways.

is caused by an imbalance of hormones.

Diabetes Mellitus

Diabetes mellitus is actually a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both.

Two broad categories:

Type 1, insulin-dependent diabetes mellitus (IDDM)

Type 2, non–insulin-dependent diabetes mellitus (NIDDM)

The ADA/world health organization(WHO) guidelines recommend the following categories ofdiabetes:

■ Type 1 diabetes ■ Type 2 diabetes ■ Other specific types of diabetes ■ Gestational diabetes mellitus

(GDM)

Type 1 Diabetes

Juvenile Onset Insulin Dependent Diabetes Mellitus Brittle Diabetes Ketosis-Prone Diabetes

is characterized by inappropriate hyperglycemia primarily a result of pancreatic islet –cell destruction and a tendency to ketoacidosis.

a result of cellular-mediated autoimmune destruction of the cells of the pancreas, causing an absolute deficiency of insulin secretion.

constitutes only 10% to 20% of all cases of diabetes commonly occurs in childhood and adolescence. usually initiated by an environmental factor or infection (usually a

virus) in individuals with a genetic predisposition and causes the immune destruction of the cells of the pancreas and, therefore, a decreased production of insulin.

CHARACTERISTICS:

abrupt onset

insulin dependen

ce

ketosis tendency

Signs and Symptoms:

Polydipsia (excessive

thirst)

polyphagia (increased

food intake)

Polyuria (increased urination)

rapid weight loss

Hyperventilation

mental confusion

possible loss of

consciousness

(due to increased glucose to

brain)

One or more of the following markers are found in 85% to 90% of individuals with fasting hyperglycemia:

Islet cell autoantibodies

insulin autoantibodies

glutamic acid decarboxylase autoantibodies

tyrosine phosphatase

IA-2 and IA-2B autoantibodies

Idiopathic Type 1 Diabetes

is a form of type 1 diabetes that has no known etiology, is strongly inherited, and does not have -cell autoimmunity.

Individuals with this form of diabetes have episodic requirements for insulin replacement.

Type 2 Diabetes Mellitus

Non-Insulin Dependent Diabetes Mellitus Adult-type/Maturity Onset Diabetes Mellitus Stable Diabetes Ketosis-resistant Diabetes Receptor-Deficient Diabetes Mellitus

Is characterized by hyperglycemia as a result of an individual’s resistance to insulin with an insulin secretory defect.

This resistance results in a relative, not an absolute, insulin deficiency.

Constitutes the majority of the diabetes cases. Most patients in this type are obese or have an increased

percentage of body fat distribution in the abdominal region.

is associated with a strong genetic predisposition, with patients at increased risk with an increase in age, obesity, and lack of physical exercise.

Characteristics usually include adult onset of the disease and milder symptoms than in type 1, with ketoacidosis seldom occurring.

However, these patients are more likely to go into a hyperosmolar coma and are at an increased risk of developing macrovascular and microvascular complications.

TYPE I DIABETES

TYPE II DIABETES

PATHOGENESIS B-cells destruction

Insulin resistance

INCIDENCE RATE 10-15% 90-95%

ONSET Childhood/teens Over 40 y/o

RISK FACTORS Genetic;auto-immune

Genetic, obesity, lifestyle

C-PEPTIDE LEVELS Decreased or undetectable

Detectable

PRE-DIABETES Auto-antibodies(+)

Auto-antibodies(-)

SYMPTOMATOLOGY

Symptoms develop abruptly

Symptoms develop gradually

KETOSIS Common;poorly controlled

Rare

MEDICATION Insulin absolute Oral agents

Other specific types of diabetes

are associated with certain conditions (secondary), including genetic defects of -cell function or insulin action, pancreatic disease, diseases of endocrine origin, drug- or chemical-induced insulin receptor abnormalities, and certain genetic syndromes.

The characteristics and prognosis of this form of diabetes depend on the primary disorder.

Maturity-onset Diabetes Of Youth (MODY) is a rare form of diabetes that is inherited in an

autosomal dominant fashion.

Gestational Diabetes Mellitus(GDM) is “any degree of glucose intolerance with onset or first

recognition during pregnancy.” Causes of GDM include metabolic and hormonal changes. Patients with GDM frequently return to normal postpartum. However, this disease is associated with increased perinatal

complications and an increased risk for development of diabetes in later years.

Infants born to mothers with diabetes are at increased risk for respiratory distress syndrome, hypocalcemia, and hyperbilirubinemia.

Fetal insulin secretion is stimulated in the neonate of a mother with diabetes.

However, when the infant is born and the umbilical cord is severed, the infant’s oversupply of glucose is abruptly terminated, causing severe hypoglycemia.

Pathophysiology of Diabetes Mellitus

In both type 1 and type 2 diabetes, the individual will be hyperglycemic, which can be severe.

Glucosuria

• can also occur after the renal tubular transporter system for glucose becomes saturated.

• 160-180 mg/dL– Renal Threshold• As hepatic glucose overproduction continues, the plasma

glucose concentration reaches a plateau around 300 to 500 mg/dL (17–28 mmol/L).

• Provided renal output is maintained, glucose excretion will match the overproduction, causing the plateau.

• has a higher tendency to produce ketones.

type 1 diabetes:

• seldom generate ketones but instead have a greater tendency to develop hyperosmolar nonketotic states.

type 2 diabetes:

• The difference in glucagon and insulin concentrations in these two groups appears to be responsible for the generation of ketones through increased -oxidation.

• there is an absence of insulin with an excess of glucagon.

• This permits gluconeogenesis and lipolysis to occur.

• Presence of Ketone bodies.

type 1:

• insulin is present, as is (at times) hyperinsulinemia; therefore, glucagon is attenuated.

• Fatty acid oxidation is inhibited in type 2. • No lipolysis, no Ketone bodies.

type 2:

Type II Diabetes: • Mortality is high with this condition.• Ketones are not observed because the severe

hyperosmolar state inhibits the ability of glucagon to stimulate lipolysis.

NONKETOTIC HYPEROSMOLAR COMA • plasma glucose values exceeding 1,000 mg/dL (55

mmol/L), normal or elevated plasma sodium and potassium, slightly decreased bicarbonate, elevated blood urea nitrogen (BUN) and creatinine, and an elevated osmolality (greater than 320 mOsm/dL).

• The gross elevation in glucose and osmolality, the elevation in BUN, and the absence of ketones distinguish this condition from diabetic ketoacidosis.

Criteria for Testing for Prediabetesand Diabetes

Acc. to ADA: >45 years: Normal FBS result: should have their FBS tested every 3 years Abnormal FBS result: should have their FBS tested more

frequently Overweight individuals(high BMI), testing should be carried out

at an earlier age or more frequently

The ff. are risk factors:▪ ■ Habitually physically inactive▪ ■ Family history of diabetes in a first-degree relative▪ ■ In a high-risk minority population (e.g., African American,

Latino, Native American, Asian American, and Pacific Islander)

▪ ■ History of cardiovascular disease

Cont.: Criteria for Testing for Prediabetes and Diabetes

■ History of GDM or delivering a baby weighing more than 9 lb (4.1 kg)

■ Hypertension (blood pressure 140/90 mm Hg) ■ Low high-density lipoprotein (HDL) cholesterol

concentrations (35 mg/dL [0.90 mmol/L]) ■ Elevated triglyceride concentrations 250 mg/dL (2.82

mmol/L) History of impaired fasting glucose/impaired glucose

tolerance ■ Women with polycystic ovarian syndrome (PCOS) ■ Other clinical conditions associated with insulin

resistance (e.g., severe obesity and acanthosis nigricans)

Criteria for the Diagnosis of Diabetes Mellitus

Three methods of diagnosis are suggested: (1) symptoms of diabetes plus a random plasma glucose level of 200

mg/dL (2) a fasting plasma glucose of 126 mg/dL (3) an oral glucose tolerance test (OGTT) with a 2-hour postload (75-g

glucose load) level 200 mg/dL

Impaired Fasting Glucose Group First, those patients with fasting glucose levels 100 mg/dL but 126

mg/dL

Impaired Glucose Tolerance Group Another set of patients who had 2-hour OGTT levels of 140 mg/dL but

200 mg/dL

Prediabetes Patients with impaired fasting glucose and/or impaired glucose

tolerance , indicating the relatively high risk for the development of diabetes in these patients.

Criteria for the Testing and Diagnosis ofGestational Diabetes Mellitus

The diagnostic criteria for gestational diabetes follow the guidelines established by the American College of Obstetrics and Gynecology.

The criteria for women at high risk include any of the

following: age older than 25 years Overweight strong family history of diabetes history of abnormal glucose metabolism history of a poor obstetric outcome presence of glycosuria diagnosis of PCOS member of an ethnic/racial group with a high prevalence of diabetes

(e.g., Hispanic American, Native American, Asian American, African American, Pacific Islander)

FBS: The first step in screening for gestational diabetes should

In the absence of a positive confirmation, evaluation for gestational diabetes in women with average or high-risk characteristics should follow one of two approaches.

The one-step approach would be the immediate performance of a 3-hour Oral Glucose Tolerance Test(OGTT)without prior screening.

GDM is diagnosed when any two of the following four values are met or exceeded: fasting, 95 mg/dL 1 hour, 180 mg/dL 2 hours, 155 mg/dL 3 hours, 140 mg/dL

HYPOGLYCEMIA

involves decreased plasma glucose levels and can have many causes—some are transient and relatively insignificant, but others can be life threatening.

65 and 70 mg/dL (3.6–3.9 mmol/L) plasma glucose concentration at which glucagon and

other glycemic factors are released 50 to 55 mg/dL (2.8–3.0 mmol/L)

observable symptoms of hypoglycemia appear

The warning signs and symptoms of hypoglycemia are all related to the central nervous system.

The release of epinephrine into the systemic circulation and of norepinephrine at nerve endings of specific neurons act in unison with glucagon to increase plasma glucose.

Glucagon is released from the islet cells of the pancreas and inhibits insulin.

Epinephrine is released from the adrenal gland and increases glucose metabolism and inhibits insulin. In addition, cortisol and growth hormone are released and increase glucose metabolism.

Symptoms

increased hunger Sweating Nausea

Vomiting Dizziness Nervousness

Shakingblurring of speech and

sight

mental confusion

Methods of Glucose Determination

I. Chemical Methods A. Reduction-Oxidation Method▪ 1. Alkaline Copper Reduction▪ a. Folin Wu▪ b. Nelson Somogyi▪ c. Neocuprine method▪ d. Shaffer Hartmann Somogyi▪ e. Benedict’s Method

▪ 2. Alkaline Ferric Reduction▪ a. Hagedorn Jensen▪ b. Condensation Methods▪ 1.) with Phenols▪ 2.)with Aromatic amines

II. Enzymatic Methods A. Glucose Oxidase B. Hexokinase

III. Home Monitoring Glucose Method IV. Methods for Testing Urine Glucose

I. Chemical Methods

A. Reduction-Oxidation Methods 1. Alkaline Copper Reduction

Method Principle: Glucose in hot alkaline solution readily

reduces cupric ions to cuprous ions forming cuprous oxide.

a. Folin Wu Cuprous ions react with

phosphomolybdic acid forming Prussian blue phospho -molybdenum oxide.

The reaction is measured at 520 nm. The method requires deproteinization to

remove chromogens.

b. Nelson Somogyi method Cuprous ions react with arsenomolybdic

acid forming Prussian blue arsenomolybdenum oxide.

The method is considered to be specific for glucose since during deproteinization process.

c. Neocuprine method Cuprous ions forms an orange colored

complex with neocuprine reagent(2,9 dimethyl, 1, 10-phenanthroline hydrochloride) producing cuprous-neocuproine complex

d. Shaffer Hartmann Somogyi Method Cuprous ion react with iodine in acidic

solution and the excess iodine is titrated with thiosulfate(colorless)

e. Benedict’s method A modification of the Folin Wu Method

2. Alkaline Ferric Reduction Method Principle: Glucose reduces ferricyanide to form a colorless

ferrocyanide.

a. Hagedorn Jensen Method The decrease in color of ferricyanide is measured

in spectrophotometer at 420 nm(inverse colorimetry). The result is affected by elevated values of creatinine and uric acid. This meyhod is widely used in Technicon Auto Analyzer System.

B. Condensation Methods 1. Condensation with Phenols

Hydroxyethyl furfural is form glucose in hot acidic solution.

The aldehyde of this product condenses with phenol forming colored compound.

2. Condensation with Aromatic Amines The aldehyde group of glucose condenses with

aromatic amines in hot acetic acid solution to form colored derivatives.

The most widely used is ortho toluidine method, others are aniline, 2-amio phenyl.

a. Ortho Toluidine method▪ Consired to be the most specific non-enzymatic method of

glucose determination▪ Principle:▪ O-toluidine forms an equilibrium mixture of glycosylamine

and Schiff’s base forming green color with maximum absorption at 630 nm.

II. Enzymatic Method

1. Glucose Oxidase Method Principle: This enzyme catalyzes the oxidation of glucose to

gluconic acid and water.

a. Saifer Gernstenfield Method (Colorimetric glucose oxidase) Glucose oxidase catalyzes the oxidation of oxidation of

glucose molecular oxygen to form gluconic acid and water.

The colorimetric reaction is then catalyzes by peroxidase wherein colorless oxygen acceptor is a colored product.

b. Polarographic Glucose Oxidase Method

The oxygen consumed in the oxidation process of glucose to gluconic acid is measured using a polarographic oxygen electrode.

2. Hexokinase Method Considered to be the most highly specific for

glucose determination. Principle: Hexokinase enzyme catalyzes the phosphorylation of

glucose by ATP forming glucose6-phosphate dehydrogenase(G6PD) catalyzes the reaction of G-6-P with NADP to form 6-phosphogluconate and NADPH. The reaction is measured at 340 nm.

Measuring the reaction at visible region is made possible by using phenazine methosulfate(PMS) and read at 520 nm.

III. Home Monitoring Glucose Methods:

1. Dextrostics (Ames Co.) Using only a drop of blood, the

reaction on the reagent pad is read in reflectance colorimeter.

a. bG Chemstrip The reaction on the strip is compared

against a color chart on by using Accucheck bG meter.

IV. Methods for Urine Glucose Determination:

1. Clinitest Table Test 2. Reagent Strip Test 3. Benedict’s Method

Sample/Test for Glucose Determination:

1. Fasting Blood Sugar(FBS) 6-8 hrs fasting Screening test for DM

2. Random Blood Sugar(RBS) Random sample Indicated during insulin shock and hyper

glycemic ketonic coma 3. Post Prandial Blood Sugar(PPBS)

1-5 hours after taking regular meal

4. Glycosylated Hemoglobin(HbA1c) Glucose/hemoglobin derivation that

increases as the level of glucose increases. Indication of glucose control over the last

three months Monitoring of diet and medication

(effectiveness of treatment) Methods used: A. Column chromatography B. Electrophoresis

5. Fructosamine Glycosylated albumin and other protein Gives a clear picture of more short-term

glucose levels(serum albumin has a half-life of 2-3 weeks)

Methods: A. Column Chromatography B. Colorimetric Assay

6. Glucose Tolerance Test(GTT) Also called glucose challenge A glucose load is given, the blood glucose rises

higher and returns to a baseline.

A. Oral Glucose Tolerance Test(OGTT) fasting, 95 mg/dL 1 hour, 180 mg/dL 2 hours, 155 mg/dL 3 hours, 140 mg/dL

B. Intravenous Glucose Tolerance Test(IVGTT) Glucose load given intravenously

C. Other Tolerance Tests: 1. Insulin Tolerance Test

Evaluates sensitivity to insulin and the function of the anterior pituitary gland and the adrenal cortex

2. Insulin Glucose Tolerance Test Glucose is administered orally 30

minutes after injection of insulin

3. Galactose Tolerance Test Detects impaired glycogenolysis or

severe liver damage. 4. Leucine Tolerance Test

Used for children suffering from hypoglycemic episodes.

Genetic Defects in Carbohydrate Metabolism

Glucose-6-phosphatase Deficiency Type 1 The most common congenital form of

glycogen storage disease also called von Gierke disease an autosomal recessive disease is characterized by severe hypoglycemia that

coincides with metabolic acidosis, ketonemia, and elevated lactate and alanine.

Hypoglycemia occurs because glycogen cannot be converted back to glucose by way of hepatic glycogenolysis.

A glycogen buildup is found in the liver, causing hepatomegaly. A liver biopsy will show a positive glycogen stain.

The patients usually have severe hypoglycemia, hyperlipidemia, uricemia, and growth retardation.

Although the glycogen accumulation is irreversible, the disease can be kept under control by avoiding the development of hypoglycemia.

Galactosemia

a cause of failure to thrive syndrome in infants, is a congenital deficiency of one of three enzymes involved in galactose metabolism, resulting in increased levels of galactose in plasma.

The most common enzyme deficiency is galactose-1-phosphate uridyl transferase.

occurs because of the inhibition of glycogenolysis and is accompanied by diarrhea and vomiting.

Galactose must be removed from the diet to prevent the development of irreversible complications. If left untreated, the patient will develop mental retardation and cataracts.

The disorder can be identified by measuring erythrocyte galactose-1-phosphate uridyltransferase activity.

Laboratory findings include hypoglycemia, hyperbilirubinemia, and galactose accumulation in the blood, tissue, and urine following milk ingestion.

Another enzyme deficiency, fructose-1-phosphate aldolase deficiency, causes nausea and hypoglycemia after fructose ingestion.

Specific inborn errors of amino acid metabolism and long-chain fatty acid oxidation are also responsible for hypoglycemia.

There are also alimentary and idiopathic hypoglycemias.

Alimentary hypoglycemia appears to be caused by an increase in the release of

insulin in response to rapid absorption of nutrients after a meal or the rapid secretion of insulin-releasing gastric factors.

Idiopathic postprandial hypoglycemia is a controversial diagnosis that may be overused.

Methods of Glucose Measurement

serum, plasma, or whole blood. The glucose concentration in whole blood is approximately

11% lower than the glucose concentration plasma. Serum or plasma must be refrigerated and separated from

the cells within 1 h to prevent substantial loss of glucose by the cellular fraction, particularly if the white blood cell count is elevated.

Sodium fluoride ions (gray-top tubes) are often used as an anticoagulant and preservative of whole blood, particularly if analysis is delayed. The fluoride inhibits glycolytic enzymes.

However, although fluoride maintains long-term glucose stability, the rates of decline of glucose in the first hour after sample collection in tubes with and without fluoride are virtually identical. Therefore, the plasma should be separated from the cells as soon as possible.

Fasting blood glucose (FBG) should be obtained in the morning after an approximately 8 to 10hours fast (not longer than 16 hours).

Fasting plasma glucose values have a diurnal variation with the mean FBG higher in the morning than in the afternoon.

Diabetes in patients tested in the afternoon may be missed because of this variation.

Cerebrospinal fluid and urine can also be analyzed. Urine glucose measurement is not used in diabetes

diagnosis; however, some patients use this measurement for monitoring purposes.

Fasting glucose in whole blood is 15% lower than in serum/plasma

Venous blood glucose is 7 mg/dL lower than capillary blood; capillary blood glucose is same with arterial blood glucose

CSF glucose concentrations should be approximately 60% of the plasma concentrations

Peritoneal Fluid glucose is same with plasma

Specimen consideration:

Serum or plasma must be separated from the cells within one hour to prevent losses of glucose(preferably within 30 minutes)

At room temperature(20-25 degrees celsius), glycolysis decreases glucose by 5-7%/hour(5-10 mg/dL) in normal un-centrifuged coagulated blood

At refrigerated temperature(4 degrees celsius), glucose is metabolized at the rate of about 1-2 mg/dL/hour

WBC and RBC metabolize glucose resulting in decreased value in clotted, uncentrifuged blood

Ketones

The ketone bodies are produced by the liver through metabolism of fatty acids to provide a ready energy source from stored lipids at times of low carbohydrate availability.

The three ketone bodies are: acetone (2%), acetoacetic acid (20%) β-hydroxybutyric acid (78%)

A low level of ketone bodies are present in the body at all times.

However, Ketones increases in cases of carbohydrate deprivation or decreased carbohydrate use: diabetes mellitus starvation/fasting high-fat diets prolonged vomiting glycogen storage disease

ketonemia refers to the accumulation of ketones in blood

Ketonuria refers to accumulation of ketones in urine.

The measurement of ketones is recommended for patients with type 1 diabetes during acute illness, stress, pregnancy, or elevated blood glucose levels above 300 mg/dL or when the patient has signs of ketoacidosis.

Ketone Determination:

The specimen requirement is fresh serum or urine; the sample should be tightly stoppered and analyzed immediately.

No method used for determination of ketones reacts with all three ketone bodies.

Gerhardt’s Test used ferric chloride reacted with acetoacetic acid to produce a red

color. The procedure had many interfering substances, including salicylates.

Sodium nitroprusside (NaFe- [CN]5NO) reacts with acetoacetic acid in an alkaline pH to form a purple color. If

the reagent contains glycerin, then acetone is also detected. This method is used with the urine reagent strip test and Acetest

tablets.

Microalbuminuria

Diabetes mellitus causes progressive changes to the kidneys and ultimately results in diabetic renal nephropathy.

This complication progresses over years and may be delayed by aggressive glycemic control.

An early sign that nephropathy is occurring is an increase in urinary albumin.

Microalbumin measurements are useful to assist in diagnosis at an early stage and before the development of proteinuria.

An annual assessment of kidney function by the determination of urinary albumin excretion is recommended for diabetic patients.

Microalbuminuria

persistent albuminuria range of 30 to 299 mg/24 h albumin-creatinine ratio: 30 to 300 g/mg.

Clinical proteinuria or macroalbuminuria is established with an albumin-creatinine ratio of 300 mg/24 h or an albumin-creatinine ratio of 300 g/mg.

three methods for microalbuminuria screening: random spot collection--is the preferred method. 24 hour urine collection timed 4-hour overnight collection

Islet Autoantibody and Insulin Testing

The presence of autoantibodies to the islet cells of the pancreas is characteristic of type 1 diabetes.

However, islet autoantibody testing is not currently recommended for routine screening for diabetes diagnosis.

In the future, this testing might identify at risk, prediabetic patients.

Insulin measurements are not required for the diagnosis of diabetes mellitus, but in certain hypoglycemic states, it is important to know the concentration of insulin in relation to the plasma glucose concentration.