Investigations
1st investigations to order
random plasma glucose
Test
Hyperglycaemia in hospitalised patients is defined as blood glucose >7.8 mmol/L (>140 mg/dL).[1] Glucose levels <3.9 mmol/L (<70 mg/dL) are considered clinically important hypoglycaemic events independent of the severity of acute hypoglycaemic symptoms.[1]
As a diagnostic screening test, random plasma glucose of ≥11.1 mmol/L (≥200 mg/dL) accompanied by symptoms of hyperglycaemia (polyuria, polydipsia, weight loss) or hyperglycaemic crisis confirms a diagnosis of diabetes.[1]
Result
hyperglycaemia in hospitalised patients: blood glucose >7.8 mmol/L (>140 mg/dL); level 1 hypoglycaemia: blood glucose <3.9 mmol/L (<70 mg/dL) and ≥3.0 mmol/L (≥54 mg/dL); level 2 hypoglycaemia: blood glucose <3.0 mmol/L (<54 mg/dL); level 3 hypoglycaemia: severe event characterised by altered mental and/or physical status requiring assistance for treatment of hypoglycaemia
HbA1c
Test
HbA1c ≥48 mmol/mol (≥6.5%) on two separate occasions, or a single HbA1c ≥48 mmol/mol (≥6.5%) in combination with either a fasting glucose ≥7 mmol/L (≥126 mg/dL) or a random plasma glucose of ≥11.1 mmol/L (≥200 mg/dL), is diagnostic of diabetes.[1]
The oral glucose tolerance test is not usually done during hospitalisation. HbA1c may be useful in differentiating previously unrecognised diabetes from transient hyperglycaemia. A normal HbA1c in the face of new hyperglycaemia suggests transient hyperglycaemia, while an elevated level suggests long-standing diabetes. HbA1c can also help assess prior treatment and control of known diabetes.[1]
Result
≥48 mmol/mol (≥6.5%) suggests chronic hyperglycaemia; elevated HbA1c must be confirmed on a separate occasion
serum urea, creatinine, and eGFR
Test
Renal insufficiency is a risk factor for hypoglycaemia.
Result
may be abnormal in diabetic nephropathy
spot urine albumin/creatinine ratio
Test
Microalbuminuria has historically been defined as 3.4 to 33.8 mg/mmol (30-299 micrograms/mg) creatinine.
Macroalbuminuria has historically been defined as ≥33.9 mg/mmol (≥300 micrograms/mg) creatinine.
Result
<3.4 mg/mmol (<30 micrograms/mg) creatinine is normal and excludes diabetic nephropathy
serum ketones
Test
Need to correlate with clinical picture, because serum ketones may be elevated in starvation.
Beta-hydroxybutyrate is elevated when >300 micromol/L (>3 mg/dL).
Urine ketones are not recommended as they may reflect the patient's state several hours ago.
Result
may be positive
Investigations to consider
post-discharge fasting plasma glucose or HbA1c
Test
All patients admitted to hospital with new-onset hyperglycaemia should be assessed for the presence of diabetes with a post-discharge fasting glucose or HbA1c.
Abnormal results need to be confirmed on a separate day.
Result
≥7 mmol/L (≥126 mg/dL) or HbA1c ≥48 mmol/mol (≥6.5%) is diagnostic of diabetes mellitus
post-discharge 2-hour post-load glucose after 75 g oral glucose
Test
All patients admitted to hospital with new-onset hyperglycaemia should be assessed for the presence of diabetes with a follow-up test. Testing 2-hour post-load glucose after 75 g oral glucose may be needed when diabetes is strongly suspected post-discharge, but fasting plasma glucose (<7 mmol/L [<126 mg/dL]) or HbA1c is not diagnostic. Patients should be advised to consume a varied diet with at least 150 g of carbohydrate on the 3 days prior to testing, as fasting and carbohydrate restriction can falsely increase plasma glucose levels.[1]
Abnormal results need to be confirmed on a separate day.
Result
2-hour plasma glucose ≥11.1 mmol/L (≥200 mg/dL) is diagnostic of diabetes mellitus
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