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Blood Sciences Test


C-peptide – Clotted serum sample
Room temp 4°C -20°C or below
Separated/centrifuged 24 hours 5 days Stable
On cells 12 hours 5 days N/A


C-peptide – EDTA sample

Room temp 4°C

-20°C or below

Separated/centrifuged 48 hours 5 days Stable
On cells 48 hours 5 days N/A


C-peptide key messages:

EDTA whole blood samples for C-peptide analysis can be sent at room temperature to be received within 48 hours of sample collection.

Serum that has been separated is stable for 24 hours at room temperature, or 5 days at 4 °C.

Clotted samples that have been stored at 4 °C are stable for up to 5 days, whether centrifuged (separated) or not.

Please note, that haemolysis hugely impacts C-peptide stability.



Test Usage

C-peptides are fragments derived from endogenous, but not exogenous, insulin and therefore may be used to assess endogenous insulin secretion even in patients who receive exogenous insulin therapy.

C-peptide testing is used in the investigation of unexplained hypoglycaemia and in the management of patients with insulin treated diabetes.

Investigation of hypoglycaemia:

A C-peptide concentration greater than 300 pmol/L during a hypoglycaemic episode (concurrent glucose <3.0 mmol/L),  is inappropriately high. C-peptide is considered appropriately suppressed if less than 94 pmol/L during hypoglycaemia. Indeterminate values are 94-300 pmol/L.

Management of Insulin treated diabetes

C-peptide measurement can assist classification and management of patients who have insulin treated diabetes. Clinical thresholds and interpretation for patients with insulin treated diabetes are shown in table 1 below. As the main clinical role of the C-peptide test in diabetes is identifying or excluding very severe insulin deficiency (present in longstanding Type 1 diabetes and associated with an absolute requirement for insulin), the role of C-peptide testing in non-insulin treated patients is limited.

General interpretation

C-peptide ranges


Local test

Turnaround Time

1 day

Cannot be added on to an existing request


We welcome referrals for C-peptide monitoring. If you are a new requestor please complete the following form: New requestor form

We now also have the option to use NPEx for referral requesting.

Further information about sample requirements for this test can be found here: Plasma C Peptide – Referred Test Questionnaire v3

Further information about sample labelling requirements for this test can be found here: Specimen Labelling Procedure

Specimen Labelling Procedure
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