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• Measure glucose level in the blood• Blood sample withdrawn from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