Hba1c for diagnosis

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Hba1c for diagnosis

• Dr Karen Adamson

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a-chain
ß-chain
Glucose bound to N-terminal valine of ß-chain
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What is HbA1c? Glucose binds irreversibly to
haemoglobin in red blood cells, forming HbA1c
The higher the glucose, the higher the HbA1c
HbA1c reflects the prevailing blood glucose over
the preceding 2-3 months
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Why Measure HbA1c?

• Serial measures show how an individuals
  glucose control, and thus risk of complications,
  change in response to alterations in management
• Measure 2-6 monthly
• Set individual target levels

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What Are The Limitations of HbA1c Measurement?

• Abnormal red cell turnover
• Abnormal haemoglobin
• Renal disease
• Liver disease
• Pregnancy HbA1c falls by 0.5

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HbA1c as an Indicator of Glycaemic Control
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Available Measures of Glycaemic Control

• Fasting Plasma Glucose (FPG)
• Preferred test for diagnosis (mmol/l or mg/dL)
• Snapshot of glycaemia
• Oral Glucose Tolerance Test (OGTT)
• Response to glucose challenge, can be used to
  diagnose disease
• HbA1c (Glycated Haemoglobin)
• Long-term measurement of glycaemic control (3
  months)
• Postprandial Glucose (PPG)
• Glucose level after eating (mmol/l or mg/dL)
• Random Blood Glucose (RBG)
• Measures blood sugar at any point in time, normal
  levels not defined
• Continuous Glucose Monitoring (CGM)
• Assesses how blood glucose levels react to
  insulin, exercise and meals

measured after at least 8 hours of fasting
measured 1- 2 hours after eating
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Not suitable for HbA1C

• Rapid onset of diabetes
• Suspected T1DM see symptomatic patient
  flowchart
• Drug-induced steroids, anti-psychotics,
  immunosuppressants a fasting glucose may not be
  sufficient. Seek advice from diabetes team.
• Pancreatic disease. Seek advice from diabetes
  team.
• Pregnancy HbA1C reduced in pregnancy.
  Gestational diabetes should be diagnosed by OGTT.
  N.B. OGTT diagnostic criteria are lower than for
  the general population.
• Conditions affecting Hb turnover / HbA1C assay
• Haemoglobinopathy
• Haemolytic anaemia
• Severe blood loss, Blood transfusion
• Splenomegaly / Splenectomy
• Renal dialysis /- erythropoitein
• Anti-retrovirals, ribavarin, dapsone

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Diagnosis of diabetes mellitus in symptomatic
patients
Thirst, polyuria
Unexpected weight loss
Symptomatic patient
Recurrent infection
Blurring of vision
Discoloured/ulcerated feet

random glucose
11.1 mmol/L
or
fasting glucose
7.0 mmol/L

DIABETES
Severe symptoms
Mild symptoms
?ketotic
vomiting / dehydration
URGENT HOSPITAL ADMISSION
ketonuria (or ketonaemia)
Full assessment initiate management of Type 2
Diabetes
young age
OR
URGENT discussion with diabetes team (may need
insulin therapy)
ketones can be measured on some POC glucometers
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Diagnosis of diabetes mellitus in asymptomatic
patients
not diabetic
(repeat on separate day)
6.0 mmol/L
random glucose
repeat fasting glucose
11.1 mmol/L
high risk
Consider HbA1C
6.1 6.9 mmol/L
fasting glucose
7.0 mmol/L
INITIAL lab glucose
diabetes
7.0 mmol/L
(random OR fasting)
suitable for HbA1C?
YES
NO
(repeat blood test on a separate day)
OGTT
HbA1C
not diabetic
high risk
not diabetic
high risk
diabetes
diabetes
48 mmol/mol
42 47 mmol/mol
41 mmol/mol
fasting glucose
6.0
6.1 6.9
7.0
mmol/L
All glucose measurements used for diagnosis must
be laboratory samples
AND
OR
OR
2-hr glucose
7.7
7.8 11.0
11.1
mmol/L