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PTD - 251

Test Directory -  Insulin and C-peptide

Clinical Indications

Differential diagnosis of documented spontaneous hypoglycaemia. The measurement of both insulin and C-peptide is undertaken since in some cases of insulinoma, insulin levels may be low whereas C-peptide is almost always unequivocally raised. Both measurements are required for the identification of factitious insulin observation.
The use of insulin and C-peptide levels to assess endogenous insulin production in Type 2 diabetics is unreliable and should be restricted to patients awaiting renal/pancreatic transplant.

Request Form

Combined Pathology Blood form (Yellow/Black)

Availability

Referred test: If specific criteria is met paediatric insulin is analysed by Chemical Pathology, Great Ormond Street Hospital and adult insulin/C-Peptide analysed by St Thomas' Hospital, London.

Specific Criteria

Differential diagnosis of documented spontaneous hypoglycaemia. Samples will not normally be analysed unless simultaneous glucose analysis shows hypoglycaemia (< 2.5 mmol/L by laboratory assay).
Assessment of endogenous insulin production for patients awaiting renal/pancreatic transplant

Patient Preparation

For investigation of hypoglycaemia, a grey top (fluoride) sample must be taken simultaneously.
For assessment of endogenous insulin production: exogenous insulin suppresses endogenous insulin production. Suggested procedure is to withhold usual pre-meal insulin, give light meal and collect samples after 30 mins. Usual insulin dose can then be given.

Limitations

 

Sample must be transported to laboratory and separated within 30 minutes of collection. Patients must be bled at Basildon Hospital.

Turnaround Time

3 working days

Specimen

Serum

Volume

2 ml

Container


Red top (serum) tube or

for paediatrics a orange top (lithium heparin) tube.

A glucose must be measured in the laboratory at the same time to confirm that the patient is hypoglycaemic.

Sample must be transported to laboratory and separated within 30 minutes of collection. Patients must be bled at Basildon Hospital. 

Causes for Rejection

Not meeting specific criteria for analysis. Delay in sample reaching laboratory. 

Reference Ranges

Insulin: 18 to 173 pmol/L
C-peptide: 370 - 1,470 pmol/L
Reference: Referral laboratory

Interpretation

An interpretation of results will be provided.

Lab. Handling

Processing: Centrifuge and aliquot immediately into 2 aliquots and freeze at -20C in separating freezer (CB40), active frozen rack 110.
Referral: PIN (paediatric insulin) or IN (adults) and send or NOIN and save in separating freezer (CB40), at -20C in the saved frozen rack.

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Version 1.0 / July 2014                                                                                                          Approved by: Consultant Biochemist