Investigations
1st investigations to order
venous blood gas
Test
Take a venous (rather than arterial) blood gas in all patients with suspected diabetic ketoacidosis (DKA).[2]
Use the pH to determine the severity of DKA.
pH ≥7.0 indicates mild or moderate DKA.
pH <7.0 indicates severe DKA. Discuss these patients with critical care.
Hyperkalaemia is common.[1]
Practical tip
Exercise caution when interpreting a potassium result obtained from a blood gas analyser.
Blood gas analysers are often used as point-of-care tests, providing rapid results (e.g., within minutes) for potassium levels, which is crucial in the initial management of DKA to guide insulin infusion.
Studies have shown that measurements from blood gas analysis may underestimate serum potassium levels in DKA.[104][105]
Be aware of these potential limitations and interpret results in conjunction with clinical judgement and other laboratory data, especially when making decisions about potassium replacement therapy.
Calculate the plasma osmolality.
Plasma osmolality is typically elevated in DKA and is an indication of dehydration.[85]
Evidence: Use of a venous versus arterial blood gas
Venous blood gas measurements are widely used instead of arterial blood gas measurements and evidence from case studies suggests there is sufficient agreement between them, when combined with other clinical findings, to use a venous blood gas to guide initial treatment.
A clinical review article aimed to answer the question “can venous blood gas analysis replace arterial blood gas analysis in emergency care?”.[106]
Venous blood gas testing may have a lower risk of serious adverse events (e.g., vascular occlusion or infection), is less painful for the patient, and is technically easier to perform than arterial blood gas testing.
There is little difference in pH values between venous and arterial samples (based on 13 studies; 2009 participants, with 3 studies [295 patients] in patients with DKA).[107]
Bicarbonate values also show close agreement between venous and arterial samples (8 studies; 1211 patients).[107]
Agreement for PCO2 is poor and unpredictable (8 studies; 965 patients), but a venous PCO2 ≤45 mmHg (6 kPa) reliably excludes clinically significant hypercarbia (4 studies; 529 patients; 100% sensitivity).[107]
Agreement on lactate is close enough to categorise as high or normal (3 studies; 338 patients).[108]
Evidence regarding arteriovenous agreement for base excess is unclear (2 studies; 429 patients; only 1 study reporting close agreement).[109][110]
If data from the venous blood gas does not appear to match the patient’s clinical condition, an arterial blood gas should be performed.[106]
Result
metabolic acidosis with a raised anion gap
anion gap >16 indicates severe DKA. [ Anion Gap Opens in new window ]
blood ketones
Test
Use urinary ketones if near-patient blood ketone (beta-hydroxybutyrate [BOHB]) testing is unavailable.[2]
Practical tip
Assessment of ketones should be done at or near the bedside using point-of-care testing.[2]
Order laboratory measurements in certain circumstances, such as when blood ketone meters are ‘out of range’.
Practical tip
Bear in mind that a patient’s medications can cause errors in detecting ketone bodies.[125]
Some drugs, such as the ACE inhibitor captopril, contain sulfhydryl groups that can react with the reagent in the nitroprusside test (used to test for ketone bodies) to give a false-positive reaction.[112] Therefore, use clinical judgement and other biochemical tests in patients who are taking these medications.
Result
ketonaemia (ketones [BOHB] ≥3 mmol/L)[2]
blood glucose
Test
Hyperglycaemia (blood glucose ≥11.1 mmol/L) is common.[1]
Be aware that some patients can present with euglycaemic diabetic ketoacidosis (DKA) and have a normal blood glucose.[86] Always use pH and ketones alongside glucose to guide diagnosis and management. Manage euglycaemic DKA in the same way as hyperglycaemic DKA.[2]
Practical tip
Assessment of glucose should be done at or near the bedside using point-of-care testing.[2]
Order laboratory measurements in certain circumstances, such as when blood glucose meters are ‘out of range’.
Result
hyperglycaemia (blood glucose ≥11.1 mmol/L)
urea and electrolytes
Test
Hyponatraemia is common in diabetic ketoacidosis (DKA).[2]
Hypernatraemia with hyperglycaemia indicates severe dehydration.
Hyperkalaemia is common but hypokalaemia is an indicator of severe DKA.[2]
Hypokalaemia on arrival indicates severe total-body potassium deficit and is an indicator of severe DKA.[88] This is because the total body potassium concentration is low due to increased diuresis.
Hyperkalaemia is due to an extracellular shift of potassium caused by insulin insufficiency, hypertonicity, and acidosis.[88]
Hypomagnesaemia, hypophosphataemia, and hypochloridaemia may also be present.[2][87]
Investigations to consider
urinalysis
Test
Order if near-patient testing for ketones is unavailable or you suspect a urinary tract infection.[2]
ECG
Test
Use to look for cardiac precipitants of diabetic ketoacidosis (DKA) such as myocardial infarction and cardiac effects of electrolyte abnormalities.[2][116]
Ensure continuous cardiac monitoring and involve senior or critical care support if:[2][31]
There is persistent hypotension (systolic blood pressure <90 mmHg) or oliguria (urine output <0.5 ml/kg/hour) despite intravenous fluids
Stupor and/or coma or Glasgow Coma Scale <12 [ Glasgow Coma Scale Opens in new window ]
Blood ketones (beta-hydroxybutyrate) >6 mmol/L
Venous bicarbonate <10 mmol/L
Venous pH <7.0
Potassium <3.5 mmol/L on admission
Oxygen saturations <92% on air
Pulse >100 bpm or <60 bpm
Anion gap >16 [ Anion Gap Opens in new window ]
The patient is pregnant or has heart or kidney failure or other serious comorbidities.
pregnancy test
Test
Order in all women of childbearing age.[2]
Result
positive in pregnancy
amylase and lipase
cardiac enzymes
Test
Order troponin T or I if you suspect myocardial infarction as a precipitant.[120]
Result
elevated with myocardial infarction
creatinine kinase
Test
Elevated if rhabdomyolysis is present. This is present in around 10% of patients with diabetic ketoacidosis.[114]
Result
elevated with rhabdomyolysis
chest x-ray
liver function tests
Test
Used to screen for an underlying hepatic precipitant of diabetic ketoacidosis (DKA). Abnormal LFTs may indicate underlying liver disease (e.g., metabolic dysfunction-associated steatotic liver disease or congestive heart failure).[122][123] Chronic liver disease is a risk factor for euglycaemic DKA.[124]
Result
elevated with liver disease
blood, urine, and sputum cultures
Test
Order these if there are signs of infection. The most common are pneumonia and urinary tract infections.[70]
Patients with diabetic ketoacidosis who have an infection are usually normothermic or hypothermic due to peripheral vasoconstriction so fever may not be seen.[67]
Result
positive if infection present
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