C-Peptide 24 Hr Urine

The C-Peptide 24 Hr Urine test measures the total amount of C-peptide passed in urine over a continuous 24-hour period. C-peptide is produced when the pancreas converts proinsulin into insulin. Insulin and C-peptide are released into the bloodstream in approximately equal amounts, making C-peptide a useful marker of the body's own insulin production.

Unlike a single blood sample, a 24-hour urine collection reflects C-peptide excretion throughout an entire day. This can help account for changes in insulin secretion after meals, during fasting and during normal daily activities. The test may be used to assess pancreatic beta-cell function, support the classification of diabetes, evaluate unexplained hypoglycemia or determine whether the pancreas continues to produce insulin in a person receiving insulin injections.

The accuracy of this test depends heavily on collecting every urine sample produced during the specified 24-hour period. Missing even one collection can reduce the measured amount and produce a misleading result. Patients should carefully follow the collection instructions supplied by Focus Diagnostics or their healthcare provider.

Benefits of the Test

• Estimates the body's natural insulin production across a complete 24-hour period.
• Provides information about pancreatic beta-cell function.
• Supports evaluation and classification of different forms of diabetes.
• May help distinguish severe insulin deficiency from insulin resistance.
• Can assess insulin production in patients receiving injected insulin because injected insulin does not contain C-peptide.
• May support the investigation of recurrent or unexplained low blood glucose.
• Captures daily variation in C-peptide excretion instead of relying on a single collection time.
• Can contribute to treatment planning when interpreted with blood glucose and other laboratory results.

Why Doctors Recommend This Test

Doctors may recommend this test when they need to assess how much insulin the pancreas produces during an entire day. It can be particularly helpful when a single fasting C-peptide measurement does not provide enough information or when the clinician wants an integrated assessment of insulin secretion.

In a person with elevated blood glucose, a low urinary C-peptide result may suggest that the pancreas is producing insufficient insulin. A normal or increased result may indicate that insulin is still being produced and that insulin resistance could be contributing to high blood glucose. These patterns are not diagnostic by themselves and must be interpreted with blood glucose, HbA1c, kidney function, symptoms and medical history.

The test may also be included in the investigation of hypoglycemia. When interpreted with glucose, insulin and other related measurements, C-peptide can help doctors determine whether excess insulin originates inside the body. Because laboratory and clinical circumstances differ, additional blood tests or imaging may be required before a diagnosis is made.

Preparation Before Test

Fasting is not always required for a 24-hour urine C-peptide test. Continue your usual diet and fluid intake unless your doctor provides different instructions. Ask whether any medicine, supplement or unusual physical activity should be avoided during the collection period. Do not stop insulin, diabetes medicine or any other prescribed treatment without medical advice.

Obtain the correct collection container from Focus Diagnostics. When beginning the test, empty your bladder and discard that first urine. Record this as the start time. Collect every subsequent urine sample for the next 24 hours, including samples passed during the night. At exactly the same time the following day, empty your bladder once more and add this final sample to the container.

Store the container according to the laboratory's instructions, which may include refrigeration or keeping it in a cool place. Do not allow toilet paper, stool, menstrual blood or other materials to contaminate the specimen. If any urine is missed, spilled or not collected, contact the laboratory because the collection may need to be restarted.

Normal Reporting Time

The report is generally available within 1–2 working days after the completed 24-hour urine container reaches the laboratory. Reporting time can vary depending on sample submission time, laboratory workflow and whether the result requires additional verification. Confirm the expected schedule with the selected Focus Diagnostics centre.

Who Should Take This Test?

• People whose natural insulin production needs to be evaluated over a complete day.
• Patients undergoing assessment for type 1, type 2 or another form of diabetes.
• Individuals with diabetes whose remaining pancreatic beta-cell function requires evaluation.
• People receiving injected insulin when endogenous insulin production must be measured.
• Patients experiencing recurrent or unexplained hypoglycemia.
• Individuals being monitored after selected pancreatic treatments or procedures.
• Anyone advised to take the test by an endocrinologist, diabetologist or other healthcare professional.

Detailed Information

Insulin is produced by beta cells located in the pancreatic islets. It begins as proinsulin, which is divided into active insulin and C-peptide before release into the bloodstream. While insulin regulates glucose movement into cells, C-peptide does not perform the same glucose-lowering action. Its presence nevertheless provides a useful indication that the pancreas has released natural insulin.

C-peptide is filtered from the blood by the kidneys, and a portion is excreted in urine. Measuring the total amount excreted over 24 hours provides an integrated estimate of daily C-peptide production. However, kidney function can influence urinary C-peptide levels. Reduced filtration, abnormal urine output or other renal conditions may affect the result and should be considered during interpretation.

A low result may occur when pancreatic beta cells produce very little insulin, as may happen in type 1 diabetes, advanced pancreatic damage or following removal of pancreatic tissue. A normal or high result can occur when the pancreas continues to produce insulin, including in insulin resistance and many cases of type 2 diabetes. Elevated values can also require further assessment when symptoms of excessive insulin activity or hypoglycemia are present.

The result should not be assessed without clinical context. Reference ranges vary among laboratories according to the analytical method, units and collection procedure. The doctor may compare the result with blood glucose, fasting or stimulated serum C-peptide, insulin, HbA1c, diabetes-related antibodies and kidney-function tests.

A complete collection is essential. A value that appears low may reflect missed urine rather than reduced insulin production. For this reason, patients should record the exact start and finish times and inform the laboratory of missed or spilled samples. The report must be reviewed by a qualified healthcare professional before making decisions about diabetes medication, insulin dosing or further investigations.