How do I trace ketones in urine?

How to Test for Ketones in Urine

To trace ketones in urine, use commercially available dipsticks or tablets that utilize the nitroprusside reaction, which turns purple in the presence of ketones. Moisten the strip with freshly voided urine and compare the color to the chart after 10 seconds. 1, 2

Testing Procedure

• Use commercially available dipstick tests that contain nitroprusside reagent, which produces a purple color when it reacts with acetoacetate in urine 1
• Collect a fresh urine sample in a clean container 1
• Dip the test strip into the urine sample, ensuring it is fully moistened 1
• Remove the strip and wait approximately 10 seconds (follow specific manufacturer instructions) 1
• Compare the resulting color change to the color chart provided with the test strips to determine ketone levels 1

Optimal Timing for Testing

• The highest detection rates (>90%) for ketones in urine occur in the early morning and post-dinner urine samples 3
• First morning urine and evening samples (around 22:00) typically show the highest concentration of ketones in individuals following ketogenic diets 3
• For diabetic patients monitoring for ketosis, testing should be performed during illness, stress, or when blood glucose is elevated 2

Interpretation of Results

• Normally, ketone concentrations in urine are below detection limits of commercial testing methods 1, 2
• Positive ketone readings in diabetic patients, especially those with type 1 diabetes, may indicate impending or established diabetic ketoacidosis (DKA) 1, 2
• The presence of urine ketones is highly sensitive for DKA with high negative predictive value, making it useful for ruling out DKA 1
• In non-diabetic individuals, positive ketone readings can be found during fasting, after exercise, and in up to 30% of first morning urine specimens from pregnant women 2

Limitations of Urine Ketone Testing

• Urine ketone tests using nitroprusside reagents only detect acetoacetate and acetone, not β-hydroxybutyrate (bOHB), which is the predominant ketone body in DKA 1, 4
• False-positive results can occur with highly colored urine 1, 2
• False-negative readings can occur when test strips have been exposed to air for an extended period or when urine specimens are highly acidic 2
• During treatment of DKA, urine ketone levels may appear to increase even as the condition improves, as β-hydroxybutyrate is converted to acetoacetate 4

Blood vs. Urine Ketone Testing

• Blood ketone testing that measures β-hydroxybutyrate directly is preferred over urine ketone testing for diagnosis and monitoring of DKA 1, 2, 5
• Specific measurement of β-hydroxybutyrate in blood should be used for diagnosis of DKA and may be used for monitoring during treatment 1
• Blood ketone determinations that rely on the nitroprusside reaction should not be used to monitor treatment of DKA 1
• Children with type 1 diabetes who used blood ketone testing had almost half the number of emergency department visits or hospitalizations compared to those using urine ketone testing 1

When to Test for Ketones

• Individuals who are prone to ketosis (those with type 1 diabetes, history of DKA, or treated with SGLT2 inhibitors) should measure ketones when they have unexplained hyperglycemia or symptoms of ketosis 1, 5
• Testing is recommended during illness, stress, or when blood glucose is elevated 2
• Individuals treated with SGLT2 inhibitors should check ketone levels at any sign of illness, as these medications increase the risk of DKA, even with relatively normal blood glucose levels 1, 5