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Impact of the New Diagnostic Criteria

Physicians may be concerned that the new diagnostic

criteria for diabetes mellitus, including the lower cutoff

for fasting plasma glucose levels, may greatly increase

the number of people who are diagnosed with diabetes

mellitus in their practices.

Concerns about overdiagnosis include the harm created

by anxiety, the risks and costs of unnecessary treatment,

and possible insurance discrimination, especially if the

condition that is being diagnosed is relatively benign or if

no effective treatment is available.

On the other hand, underdiagnosing a condition is

harmful if early treatment can make a difference in patient

outcome, especially if the treatment is relatively benign

and inexpensive.

It is true that a rigorous screening program will increase

the number of persons who are diagnosed with diabetes

mellitus. However, currently only half of the people who

have diabetes mellitus according to the old criteria have

not been diagnosed and may remain undiagnosed for up

to 10 years.

People who are asymptomatic and underdiagnosed

continue to develop the complications of diabetes mellitus.

Screening Recommendations

The expert committee provided guidelines governing

the selection of patients to be tested for diabetes and the

frequency of that testing (Table 17.3). Testing should be

considered for all persons who are 45 years of older and

should be repeated at 3 years intervals.

Testing should be considered at a younger age and

be performed more frequently in persons who are

obese (120% of desirable body weight or greater or a

body mass index of 27 kg per m2

 or greater); who have

a first-degree relative with diabetes mellitus; who have

delivered a baby weighing more than 4.032 g (9 lb), or

who were diagnosed with gestational diabetes mellitus

during pregnancy; are hypertensive; or have a highdensity lipoprotein level of 35 mg per dL (0.90 mmol per

L) or lower and/or a trigly-ceride level of 250 mg per dL

(2.83 mmol per L) or higher. In addition, any patient with

440 Concise Book of Medical Laboratory Technology: Methods and Interpretations impaired glucohomeostasis should be reevaluated on a

more frequent basis.

The expert committee recommended that screening for

gestational diabetes mellitus should be reserved for use

in women who meet one or more of the following criteria:

25 years of age older, obese (defined as more than 120%

above their desirable body weight), a family history of a

first-degree relative with diabetes mellitus, and belong to

high-risk ethnic population.

Final Comment

The changes recommended by the expert committee for

the diagnosis of diabetes mellitus should prove beneficial

to patients. Measurement of fasting plasma glucose levels

should be more acceptable to the patients than the oral

glucose tolerance test and can be readily incorporated with

fasting lipid determinations. Identifying asymptomatic

persons earlier in the disease process will allow earlier

institution of lifestyle changes and medical therapy that

may decrease the complications of hyperglycemia. The

National Diabetes Data Group (US) emphasizes that

these changes in diagnostic criteria have not changed the

treatment goals in patients with diabetes mellitus. These

goals include maintaining a fasting plasma glucose level of

less than 120 mg per dL (6.65 mmol per L) and a glucose

hemoglobin measurement of less than 7.0%.

Conventional Diagnostic Tests

Oral Glucose Tolerance Test (OGTT)

This is performed to establish a diagnosis in:

1. Patients with transient or sustained glycosuria who

have no clinical symptoms of diabetes (polyuria) and

with normal fasting and post-prandial blood glucose

levels.

2. Patients with symptoms of diabetes but with no

glycosuria and normal fasting level.

3. Persons with a strong family history of diabetes but

with no overt diabetes.

4. Patients whose glycosuria is associated with pregnancy,

thyrotoxicosis, liver disease, and/or infections.

5. Women who have characteristically large babies (> 9

lbs) or individuals who were large babies.

6. Patients with neuropathies and retinopathies of

undetermined origin.

The patient should ingest a daily diet of atleast 300 g

of carbohydrate for 3 days prior to the test. Therefore, on

an acutely ill-hospitalized patient, this test should not

be conducted. As far as possible it should be performed

on an ambulatory patient. Preferably, the test should be

performed in the morning. Various malignancies, fever,

cachexia, liver dysfunction and renal failure may be

associated with mild to moderate degrees of abnormal

GTT. There is an age-related factor that decreases glucose

tolerance and hence makes the interpretation of OGTT in

elderly subjects difficult. Timing of glucose administration

and blood sampling must be accurate.

Patient Preparation

1. Instruct the patient about the purpose and procedure

of the test:

a. Stress a normal diet with high carbohydrate

(150–300 g) for 3 days preceding the test.

b. Fasting is required for at least 10 hours before the

test and not more than 16 hours.

c. Water is permitted and encouraged.

2. Determine the patient’s weight and record it.

3. Collect urine and blood samples and test for glucose,

recording exact time of collection. Have the patient

empty his or her bladder for each specimen:

a. No liquids other than water can be taken. Have

the patient empty his or her bladder for each

urine sample.

b. No food is to be taken during the test period.

c. No alcohol to be consumed the previous evening.

TABLE 17.3: Recommendations for diabetes screening of

asymptomatic persons

Timing of the first test and repeat tests

• Test at age 45:

Repeat every three years (patients 45 years of age or older)

• Test before age 45:

Repeat more frequently than every three years if patient has

one or more of the following risk factors:

a. Obesity ≥ 120% of desirable body weight or BMI ≥ 27 kg

per m2

b. First-degree relative with diabetes mellitus

c. Member of high risk-ethnic group (Black, Hispanic,

Native American, Asian)

d. History of gestational diabetes mellitus or delivering a baby

weighing more than 4.032 g (9 lb)

e. Hypertensive (≥ 140/90 mm Hg)

f. HDL cholesterol level ≥ 35 mg per dL (0.90 mmol per L)

and/or triglyceride level ≥ 250 mg per dL (2.83 mmol per

L)

g. History of IGT or IFG on prior testing

BMI = body mass index: HDL = high density lipoprotein;

IGT = impaired glucose tolerance; IFG = impaired fasting glucose

Diabetes Mellitus: Laboratory Diagnosis 441

d. Encourage the patient to stay in bed or rest quietly during the test period. Weakness or feeling

faint may occur during test, and exercise also

changes, glucose results.

e. No smoking is allowed during the test.

f. Coffee and unusual physical exercise should be

avoided for at least 8 hours before the test.

Carbohydrate meal (or glucose) to be given in 25%

(w/v) solution according to the age.

 Age Dose

 0–18 months 2.5 g/kg

 1½–8 years 2.0 g/kg

 8–12 years 1.75 g/kg

 > 12 years 1.25 g/kg

Preferably, the samples of urine and whole blood be

taken at fasting, 30 minutes, 1, 1½, 2, 3, and 4 hours after

ingestion of the carbohydrate meal. If nausea and vomiting

occur during the test, the interpretation becomes difficult.

Interpretation

Three popular methods for evaluating GTT for diabetes

mellitus are:

1. Wilkerson point system

Time mg% plasma Points

Fasting 130 or more 1

1 h 195 or more ½

2 h 140 or more ½

3 h 130 or more 1

Two or more points are judged diagnostic of diabetes

mellitus (DM).

2. The Fajans-Conn criteria

Time mg% plasma

Fasting

1 h 195 or more

1½ h 165 or more

2 h 140 or more

A diagnosis of DM in otherwise healthy and ambulatory

individuals under age 50 is made if the above criteria are

met.

3. The university group diabetes mellitus program

The fasting 1 h, 2 h and 3 h blood glucose levels are

adjusted for plasma glucose as above, and the subject is

judged diabetic if the sum of values obtained equals 500

or more.

Abnormally, high values in the first hour with a rapid

fall to normal values or a flat curve with no appreciable rise

usually reflect primary alterations in intestinal absorption

of glucose. The former is characteristic of hyperthyroidism

and the latter of hypothyroidism or malabsorptive states.

A very flat rise in blood glucose followed by a prolonged

and pronounced hypoglycemic phase may be observed in

primary (islet cell adenoma or hyperplasia) and secondary

hyperinsulinism (hypoadrenocorticism). In the elderly,

especially in females, interpretation of OGTT must be

made in light of what is an age-dependent carbohydrate

intolerance.

Interfering Factors

1. Smoking will increase glucose level.

2. Inadequate diet (such as a weight-reducing diet)

before testing can diminish carbohydrate tolerance

and suggest a false diabetes.

3. Levels tend to increase normally in older people, the

maximum can reach 200 mg/dL.

4. Prolonged administration of oral contraceptives will

give significantly higher glucose levels in the second

hour or in later blood samples.

5. Bedrest over a lengthy period of time will influence

glucose tolerance. For this reason, the test should be

performed on ambulatory patients, not on patients

whose condition requires bedrest.

6. Infectious diseases and surgery will affect tolerance.

Two weeks of recovery should be permitted before the

test.

7. Drugs that impair glucose tolerance:

• Insulin

• Oral hypoglycemics

• Salicylates in larger doses

• Oral contraceptives

• Thiazide diuretics

• Corticosteroids

• Estrogen

• Ferrous ascorbinate

• Nicotinic acid

• Phenothiazines

• Lithium

• Metapyrone.

Discontinue these drugs for 3 days prior to test. This

test is contraindicated in patients who have had a recent

history of surgery, myocardial infarction, a labor and

delivery, for these conditions can cause erroneous results.

Record and report any reactions that may occur during

the test. Weakness, faintness, and sweating may occur

between the second and third hours. If this occurs, a blood

sample for sugar is drawn and the test is discontinued. Test

should be postponed in the event of unexpected illness,

such as fever or gastritis or if there has been ingestion

of food within 8 hours. If the fasting blood sugar is over

200 mg/dL, the GTT is usually not done. If it is done, the

patient should be monitored very carefully for severe

reaction or even coma.

442 Concise Book of Medical Laboratory Technology: Methods and Interpretations IV GTT

In patients with gastrointestinal disorders an intravenous

GTT may be done. These patients may be suffering from

sprue or malabsorption syndrome or may be postgastrectomy patients. A sterile glucose solution is given IV

(20% w/v) over a 30 minutes period in an amount of 0.5 g/

kg of ideal body weight. Similar blood collection intervals,

including a fasting specimen, are followed, and a curve is

plotted for evaluation (F, 1/2, 1, 1½, 2, 2½ and 3 hours).

In a normal individual, the fasting specimen of blood

contains a normal amount of glucose, the concentration

of any single specimen does not exceed 250 mg%, and

by 1 hour 30 minutes to 2 hours, the blood glucose

level approximately comes to the fasting level (this test,

however, is a less sensitive indicator of mild abnormalities

of carbohydrate tolerance than the standard OGTT).

Rapid IV GTT

Here a rapid IV (50% w/v) GTT (0.5 g glucose/kg ideal body

weight) to a maximum dose of 25 g may be given over a 3-4

minute period. Blood samples are obtained at intervals of

10 minutes for at least 2 hours. Under these conditions,

disappearance of glucose from blood follows an exponential

curve and a glucose disappearance constant can be

calculated. In normal subjects, glucose disappearance

usually exceeds 1.5% of the administered dose per minute,

values below 1% are compatible with diabetes mellitus.

Cortisone Glucose Tolerance Test

This may reveal prediabetic patients, especially in relatives

of known diabetics. Cortisone promotes intolerance in a

latent or mild diabetic. After performance of an initial GTT,

a standard dose of cortisone (50 mg) for adults is given

parenterally 8½ hours and again 2 hours before a regular

GTT. A positive test shows a blood glucose concentration

of 140 mg% or higher with 2 hours specimen. Follow-up

studies are necessary for such individuals.

Parenteral Administration of Glucagon or

Epinephrine

Will cause a slight elevation of blood glucose concentration

from glycogenolysis in normal subjects—this is much

greater and more sustained in diabetics. It is also a measure

of glycogen storage and release, so it may be used to study

patients suspected of having a glycogen storage disease.

IV Tolbutamide Test

Oral hypoglycemic agent administration results in

secretion of insulin from pancreas. This principle is taken

advantage to indicate (active) insulin reserve in patients.