Chronic Diabetes Case F

Gestational Diabetes Mellitus (GDM)

Clinical Pathology B

Hoa NguyenTuan Anh TranThi Thuy Duong Trang

Objectives

• Explain the tests which may have been used in the diagnosis of GDM

• Role of self-monitoring blood glucose levels in patients with GDM

• Examine various approaches to use in blood glucose monitoring devices

• Accuracy and factors which affect the accuracy of these devices

• Processes required to give patients confidence in the result obtained

What is gestational diabetes?

• Carbohydrate/glucose intolerance of variable severity

• Asymptomatic• Onset or first recognised during

pregnancy

Tests may have been used in diagnosis of GDM

• Oral glucose tolerance test

• Urine glucose test

• Blood glucose test

Oral glucose tolerance test

• Measure the body’s ability to metabolise glucose

• Used to screen pregnant women for GDM between 24 and 28 weeks of pregnancy

Oral glucose tolerance test

• Fasting 8-12 hours (overnight)• Patient’s blood sample collected• Patient given a concentrated 75g load

glucose drink• Collect blood sample after 1 hour• Collect blood sample after 2 hours

Target for oral glucose tolerance test

• If any 2 values are met or exceed, the diagnosis is GDM

• If 1 value is met or exceeded, the diagnosis is impaired glucose tolerance of pregnancy

Fasting <5.5mmol/L

1 hour <8.0mmol/L

2 hours <7.0mmol/L

Blood glucose test

• Measure glucose level in the blood• Blood sample withdrawn from

patient and sent to laboratory for testing

• Target <5.5mmol/L• Generally give first indication of

diabetes not diagnosis

Urine glucose test

• Measure glucose level in the urine• Urine sample collected and analysed by

a dye or dipstick test• Not as effective or precise as blood test

because don’t see glucose in urine below a certain threshold eg. blood level of 8.8mmol/L

Reference ranges for urine glucose test

Glucose OxidasePhenylaminophenazone(end point)

700-1050mg/L

Glucose OxidasePhenylaminophenazone(kinetic reaction)

600-950mg/L

Oxygen rate-glucose oxidase

650-1100mg/L

Hexokinase endpoint

700-1100mg/L

Role of monitoring blood glucose in GDM • Self monitoring of blood glucose in GDM

is crucial• Once diagnosed, daily monitoring

includes: at least one fasting and 1 or 2 hours postprandial

• The frequency may be decreased or increased depending on result and stage of pregnancy

Targets for glycaemic control

• Fasting capillary (venous plasma) level < 5.5mmol/L

• 1 hour postprandial capillary (venous plasma) level < 8.0mmol/L

• 2 hour postprandial capillary (venous plasma) level < 7.0mmol/L

Various approaches to blood glucose monitoring

• Many methods and devices available• Most common requires blood sample • eg. fingerstick method:

finger pricked using lancetblood placed on stripstrip placed in monitor to be measure

Problem

• Invasive • Painful • Inconvenient • Provides only snapshot

Newer devices less invasive

• Uses electrical current to measure glucose levels

• Can be placed anywhere on the body• Provides continuous and automatic

monitoring

Glucose Monitoring Devices

• One Touch Ultra (LifeScan)• FreeStyle (TheraSense)• Accu-Chek Complete (MediSense;

Abbott Labs)• Ascencia Elite (Bayer)

Differences between devices

• Sizes• Length of time for results• Amount of blood needed• Cleaning requirements• Data management

Meter accuracy

• No standards for meter accuracy and precision

• Diabetes control and complications trial (DCCT) total errors of 20% or less is acceptable (not codified)

• International organisation for standardisation (ISO) require 20% maximum system error

Factors affect accuracy

• Altitude• Hematocrit levels• Ascorbic acid (vitamin C)• Bilirubin• Creatinine• Acetaminophen (Tylenol)• Urea

Accuracy of continuous blood glucose monitor

• eg. GlucoWatch• Clinical study published in Nature

Medicine indicates accuracy of GlucoWatchCorrelation coefficient = 0.90Mean absolute error = 0.20Mean bias 5.0%

GlucoWatch

• Accuracy and precision are not affected by:Physiological factors

age, race, gender, BMI…

Environmental factorsTemperature, perspiration…

Other drugs used

Patient confidence

• Liquid control solutions• Most companies are constantly trying to

improve their products• New approach to blood glucose

monitoring provide continuous data• Better treatment plan and confidence

for patients