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Should I Get Fasting Insulin or C-Peptide or Both?
My HbA1c and random blood sugar levels are normal, but I still have some symptoms, including dry skin, recurring UTIs, unexplained weight loss, and tinnitus.
My doctor recommended two tests: fasting insulin and C-peptide. However, C-peptide is expensive for me.
Should I get only the fasting insulin test first and consider C-peptide later if the result is abnormal? Or are both tests necessary to do together? Alternatively, is C-peptide more important than fasting insulin in my situation?
I would appreciate advice from doctors on which test would be more appropriate.
Answers (10)
As such you are young, Hba1c is normal, chances of diabetes are very less. Get urine microscopic, culture, thyroid function tests, cbc, done to exclude any other reason for your symptoms.
C.peptide levels measurement is slightly more accurate tha fasting insulin levels.
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These test not required.
I
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Do consult
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With normal HbA1c and random glucose these tests are not necessary please book a consultation with me to review your symptoms and reports so we can prioritise only the investigations that are necessary
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kindly do connect and consult with me for better treatment plan and advice on your case via PRACTO app
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Dr. Sozab Malik
General Physician
2 yrs exp
Aligarh
Okay, While you are 29 Years old and your HbA1c and RBS are normal so less likely to be Type 2 Diabetes Mellitus. For recurrent UTIs do CBC, Urine microscopic and culture sensitivity. You can do Insulin Fasting but C-Peptide is more reliable and useful for diagnosing Type 1 Diabetes Mellitus.
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Dr. Karan Suneja
General Physician
4 yrs exp
Delhi
Get fasting insulin done
Next Steps
If ur problems are persisting do get the C- Peptide test done .
Health Tips
Consulting to the doctor would be better if your symptoms persist for the proper evaluation
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Dr. Divyansh Jain
General Physician
1 yrs exp
Ghaziabad
Hello,
I understand your concern regarding the cost of investigations.
Fasting insulin and C-peptide measure different aspects of insulin production, but neither is routinely necessary to diagnose diabetes.
Fasting insulin: Primarily used in selected metabolic or hypoglycaemia evaluations.
C-peptide: Helps assess the body's natural insulin production, particularly when distinguishing certain types of diabetes.
Since your HbA1c and random glucose are reportedly normal, neither test is necessarily the first priority.
However, unexplained weight loss and recurrent UTIs deserve further evaluation, even with normal blood sugar reports.
Next Steps
Consult your prescribing physician to clarify why both tests were recommended before spending money on them. Consider a laboratory fasting plasma glucose test, if not already performed, and review your previous HbA1c results. For recurrent UTIs, a urine routine examination and urine culture during symptoms may help identify infection. Unexplained weight loss warrants evaluation, including CBC, TSH, kidney function, and other tests based on clinical findings. If insulin deficiency is specifically suspected, C-peptide with simultaneous blood glucose is generally more informative than fasting insulin alone. However, it should only be ordered when clinically indicated.
Health Tips
My recommendation: Do not spend money on fasting insulin simply as a cheaper substitute for C-peptide. An abnormal fasting insulin result does not automatically indicate that C-peptide testing is required. Both tests are not routinely needed together, and the appropriate choice depends on the suspected diagnosis. Seek prompt medical evaluation if weight loss continues or you develop excessive thirst, frequent urination, fever, or worsening weakness. A targeted, cost-effective investigation plan is preferable to unnecessary testing. Wishing you good health!
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Dr. Anuj Mothsra
General Practitioner
7 yrs exp
Jhunjhunu
Can help you, kindly consult and provide detailed history for proper diagnosis and further management
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Dr. Ankita Gahlot
Obstetrician
12 yrs exp
Bangalore
With a normal HbA1c and blood sugar, your doctor is likely checking fasting insulin and C-peptide to see how your body is handling insulin before sugar levels actually rise. These two tests measure different things, insulin is the hormone level itself and C-peptide shows how much your own pancreas is producing, so they aren't fully interchangeable.
Next Steps
Fasting insulin is the more affordable first step, so start there. If it comes back high or unclear, go ahead with C-peptide rather than skipping it. Also ask your doctor about thyroid and iron studies, since dry skin, weight loss and tinnitus can point beyond insulin resistance alone.
Health Tips
Please confirm this sequencing with your prescribing doctor before deciding, since they know why both tests were recommended together for you.
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Disclaimer : The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding your medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.