CPT: 84681

Expected Turnaround Time

24 Hours

Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.

Specimen Requirements




SST (Serum), Red Top (Separate Serum)

Storage Instructions

Room Temp., Refrigerated (2-8 C)

Stability Requirements

Room temp. 72hrs., Refrigerated 7 days

Test Details

Additional Information

C-peptide is a substance – a short chain of amino acids – released into the blood as an inactive byproduct of the formation of insulin by the pancreas. The pancreas produces about the same amount of insulin and C-peptide. This test measures the amount of C-peptide in the blood or sometimes urine sample.

Insulin is a hormone that regulates the amount of sugar (glucose) in the blood. Glucose is the human body’s main source of energy. Insulin allows cells in the muscles, fat and liver to absorb glucose to be used as energy. 

Within specialized cells called beta cells in the pancreas, proinsulin, a biologically inactive molecule, is split apart. It forms one molecule of C-peptide and one molecule of insulin, vital for transporting glucose into the body’s cells and required daily. 

When insulin is released from the beta cells into the blood in response to increased levels of glucose, equal amounts of C-peptide are also released. Since C-peptide is produced at the same rate as insulin, it is useful as a marker of insulin production.

In people with Type 1 diabetes, the pancreas is not able to make insulin. They need insulin injections so the body can use glucose. People with Type 2 diabetes make insulin, but their bodies either don’t produce enough insulin or resist the effects of insulin. Some people with Type 2 diabetes need medications to help their bodies use glucose. Over time, some people with Type 2 diabetes are no longer able to make insulin. 

A C-peptide test can’t determine whether a person has diabetes. It merely indicates if the body has the ability to make its own insulin from the pancreas. 


  1. Al-Rasheed NM, Willars GB, Brunskill NJ. C-peptide signals via Galpha i to protect against TNF-alpha-mediated apoptosis of opossum kidney proximal tubular cells. J Am Soc Nephrol. 2006 Apr;17(4):986-95. [PubMed] 
  2. Zhong Z, Kotova O, Davidescu A, Ehrén I, Ekberg K, Jörnvall H, Wahren J, Chibalin AV. C-peptide stimulates Na+, K+-ATPase via activation of ERK1/2 MAP kinases in human renal tubular cells. Cell Mol Life Sci. 2004 Nov;61(21):2782-90. [PubMed] 

Statement on Medical Necessity
All ordered tests should be medically necessary for the diagnosis or detection of disease, illness, impairment, symptom, syndrome, or disorder and the results should be used in the medical management and treatment decisions for the patient. Solaris requires ICD-10 codes with each order for lab testing and both the tests ordered and the diagnosis should be documented in the provider’s medical record for the patient. The United States Department of Health and Human Services, Office of Inspector General, takes the position that a provider who orders medically unnecessary tests may be subject to civil penalties.

Panels and Profiles
Solaris offers Providers the convenience of ordering test combinations in a group at times with the flexibility to choose appropriate test(s) for individual patients. Providers should only order those tests that he or she believes are medically necessary for each patient, and a lesser inclusive profile or individual tests should be ordered if not all tests in the test combination/profile are medically necessary. All tests offered in a test combination/profile may be ordered separately as individual tests. Solaris encourages clients to contact their Solaris representative if the testing configurations shown do not meet individual needs for any reason, or if some other combination of procedures is needed.

CPT Codes
CPT Codes listed are in accordance with Current Procedural Terminology, a publication of the American Medical Association. CPT codes are the responsibility of the billing party and are listed here for informational purposes. Correct coding may vary from one carrier to another. Solaris may bill specific carriers using codes other than what is shown.


For questions or inquiries related to testing please reach out to
customerservice@solarisdx.com or contact us by phone at (844) 550-0308.