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PubMed This is a summary of 21 peer-reviewed journal articles Updated
Endocrinology · Maturity-Onset Diabetes of the Young

Testing for MODY: From Blood Work to Genetics

At a Glance

Diagnosing MODY is a multi-step process that starts with ruling out Type 1 diabetes using autoantibody tests and measuring insulin production with a C-peptide test. If blood tests and clinical risk scores suggest MODY, a genetic sequencing panel is used to confirm the exact mutation.

Getting a definitive MODY diagnosis is a step-by-step process. Because MODY can look so much like Type 1 or Type 2 diabetes, doctors use a series of “filters” to narrow down the possibilities. This journey usually moves from simple blood tests to clinical risk assessments, and finally, to the gold standard: genetic sequencing [1][2].

Step 1: Ruling Out Autoimmunity

The first step is often to check if your diabetes is caused by an immune system attack, which would indicate Type 1 diabetes (T1D).

  • Diabetes Autoantibodies: These are proteins (like GADA, IA-2A, and ZnT8A) that the body produced if it is attacking its own insulin-producing cells [1][3].
  • The MODY Connection: Because MODY is caused by a genetic mutation and not an immune problem, these antibody tests are typically negative in people with MODY [1][4]. If you test positive for these antibodies, it strongly suggests Type 1 diabetes instead [3].

Step 2: Measuring Insulin Production

If your antibodies are negative, the next question is: Is your body still making its own insulin?

  • C-Peptide Test: When the pancreas makes insulin, it releases a byproduct called C-peptide in equal amounts [1][5]. Measuring C-peptide tells doctors how much “homegrown” insulin you are still producing.
  • Why it Matters: In Type 1 diabetes, C-peptide levels usually drop to nearly zero within a few years of diagnosis [6][7]. In contrast, people with MODY often continue to produce measurable levels of C-peptide even decades after their diagnosis [8][9].
  • Timing: This test is most definitively helpful for distinguishing MODY from Type 1 diabetes 3 to 5 years after diagnosis. Newly diagnosed Type 1 patients can still have detectable C-peptide during their “honeymoon phase,” but persistent C-peptide long after diagnosis is a major “red flag” for MODY [10][11].

Step 3: Calculating Your Risk

Before ordering genetic tests, many specialists use a MODY Probability Calculator (such as the Exeter model) [12][2]. This tool combines several pieces of your medical history to give a percentage risk score, including:

  • Age at diagnosis: MODY usually appears before age 25 [13].
  • Body Mass Index (BMI): MODY patients are often (though not always) at a healthy weight, whereas Type 2 is frequently associated with a higher BMI [2].
  • Current Treatment: If you are on insulin but produce your own C-peptide, or if your blood sugar is very sensitive to oral pills, your score goes up [14][15].

Step 4: The Gold Standard (Genetic Testing)

If your risk score is high, the final step is Molecular Genetic Testing [16]. Modern labs use Next-Generation Sequencing (NGS) panels, which can scan many different MODY genes at the same time [17][13].

  • The Panel: Instead of testing one gene at a time, an NGS panel looks at a group of genes simultaneously. This is faster and more accurate for finding rare mutations [18][19].
  • The Result: A “pathogenic” or “likely pathogenic” result confirms the diagnosis and identifies your specific subtype [20]. This allows your doctor to practice precision medicine [14].

Advocating for Yourself

Genetic testing can sometimes be expensive or difficult to access due to insurance denials [21]. If you meet the clinical criteria, self-advocacy is key:

  • Ask your doctor to run your data through the Exeter MODY Probability Calculator and document the score in your chart to justify testing [12].
  • Ensure your doctor uses the correct diagnostic codes for suspected monogenic diabetes, not just general Type 1 or Type 2 codes.
  • Ask about financial assistance programs. Many specialized genetic testing laboratories offer sliding-scale payment options or patient assistance programs.
Test What it measures MODY Result
Autoantibodies Immune system attack Negative [1]
C-Peptide Natural insulin production Positive/Detectable [10]
Genetic Panel DNA mutations Mutation Found [16]

Previous: The Genetics of MODY | Return to Home | Next: Treating MODY

Common questions in this guide

How do doctors tell the difference between MODY and Type 1 diabetes?
Doctors typically use a diabetes autoantibody test. Because MODY is a genetic condition and not an immune system attack, antibody tests are usually negative in people with MODY.
What does a C-peptide test show for MODY?
A C-peptide test measures how much insulin your body is making. People with MODY usually continue to produce their own insulin and have detectable C-peptide levels, even years after diagnosis.
What is the Exeter MODY Probability Calculator?
It is a clinical tool doctors use to determine your likelihood of having MODY based on factors like your age at diagnosis, BMI, and current treatments. A high percentage score helps justify the need for specialized genetic testing.
How is a MODY diagnosis officially confirmed?
The gold standard for diagnosing MODY is molecular genetic testing. Laboratories use a Next-Generation Sequencing panel to scan multiple genes at once and identify the specific DNA mutation causing your diabetes.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Can we run a full pancreatic autoantibody panel (GADA, IA-2A, and ZnT8A) to rule out Type 1 diabetes?
  2. 2.What is my current C-peptide level, and was it taken when my blood sugar was high enough to stimulate insulin production?
  3. 3.Can we use the Exeter MODY Probability Calculator together during this visit to see if my risk score justifies genetic testing?
  4. 4.If my insurance denies genetic testing, can you help me appeal or connect me with a lab's financial assistance program?
  5. 5.If we do genetic testing, will you order a multi-gene Next-Generation Sequencing (NGS) panel rather than testing just one gene at a time?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (21)
  1. 1

    Absence of Islet Autoantibodies and Modestly Raised Glucose Values at Diabetes Diagnosis Should Lead to Testing for MODY: Lessons From a 5-Year Pediatric Swedish National Cohort Study.

    Carlsson A, Shepherd M, Ellard S, et al.

    Diabetes care 2020; (43(1)):82-89 doi:10.2337/dc19-0747.

    PMID: 31704690
  2. 2

    Maturity-Onset Diabetes of the Young (MODY): Making the Right Diagnosis to Optimize Treatment.

    Amed S, Oram R

    Canadian journal of diabetes 2016; (40(5)):449-454 doi:10.1016/j.jcjd.2016.03.002.

    PMID: 27130141
  3. 3

    Autoantibodies against ZnT8 are rare in Central-European LADA patients and absent in MODY patients, including those positive for other autoantibodies.

    Heneberg P, Šimčíková D, Čecháková M, et al.

    Journal of diabetes and its complications 2019; (33(1)):46-52 doi:10.1016/j.jdiacomp.2018.10.004.

    PMID: 30377089
  4. 4

    The unique clinical spectrum of maturity onset diabetes of the young type 3.

    Lebenthal Y, Fisch Shvalb N, Gozlan Y, et al.

    Diabetes research and clinical practice 2018; (135()):18-22 doi:10.1016/j.diabres.2017.10.024.

    PMID: 29107759
  5. 5

    Clinical heterogeneity of type 1 diabetes (T1D) found in Asia.

    Park Y, Wintergerst KA, Zhou Z

    Diabetes/metabolism research and reviews 2017; (33(7)) doi:10.1002/dmrr.2907.

    PMID: 28544229
  6. 6

    HLA-guided identification of monogenic diabetes in antibody-negative type 1 diabetes: frequency and characteristics.

    Chen Y, Yin M, Xie Y, et al.

    Diabetes & metabolism 2026; (52(2)):101741 doi:10.1016/j.diabet.2026.101741.

    PMID: 41679598
  7. 7

    Investigating misclassification of type 1 diabetes in a population-based cohort of British Pakistanis and Bangladeshis using polygenic risk scores.

    Liu T, Sankareswaran A, Paterson G, et al.

    Scientific reports 2025; (15(1)):1168 doi:10.1038/s41598-024-80348-8.

    PMID: 39805939
  8. 8

    PDX-1 related diabetes: a case series of two families highlighting challenges in MODY diagnosis.

    da Silva BT, Pinheiro AT, Saraiva M, et al.

    Acta diabetologica 2026; (63(2)):201-208 doi:10.1007/s00592-025-02614-z.

    PMID: 41201616
  9. 9

    Prolonged episodes of hypoglycaemia in HNF4A-MODY mutation carriers with IGT. Evidence of persistent hyperinsulinism into early adulthood.

    Bacon S, Kyithar MP, Condron EM, et al.

    Acta diabetologica 2016; (53(6)):965-972 doi:10.1007/s00592-016-0890-9.

    PMID: 27552834
  10. 10

    Zinc Transporter 8 Autoantibodies (ZnT8A) and a Type 1 Diabetes Genetic Risk Score Can Exclude Individuals With Type 1 Diabetes From Inappropriate Genetic Testing for Monogenic Diabetes.

    Patel KA, Weedon MN, Shields BM, et al.

    Diabetes care 2019; (42(2)):e16-e17 doi:10.2337/dc18-0373.

    PMID: 30409810
  11. 11

    C-peptide and residual β-cell function in pediatric diabetes - state of the art.

    Jamiołkowska-Sztabkowska M, Głowińska-Olszewska B, Bossowski A

    Pediatric endocrinology, diabetes, and metabolism 2021; (27(2)):123-133 doi:10.5114/pedm.2021.107165.

    PMID: 34514768
  12. 12

    A Clinical Prediction Model to Distinguish Maturity-Onset Diabetes of the Young From Type 1 and Type 2 Diabetes in the Chinese Population.

    Fu J, Ping F, Wang T, et al.

    Endocrine practice : official journal of the American College of Endocrinology and the American Association of Clinical Endocrinologists 2021; (27(8)):776-782 doi:10.1016/j.eprac.2021.05.002.

    PMID: 33991656
  13. 13

    How Recent Advances in Genomics Improve Precision Diagnosis and Personalized Care of Maturity-Onset Diabetes of the Young.

    Vaxillaire M, Froguel P, Bonnefond A

    Current diabetes reports 2019; (19(9)):79 doi:10.1007/s11892-019-1202-x.

    PMID: 31385057
  14. 14

    Clinical and genetic characterization and long-term evaluation of individuals with maturity-onset diabetes of the young (MODY): The journey towards appropriate treatment.

    Campos Franco P, Santos de Santana L, Dantas Costa-Riquetto A, et al.

    Diabetes research and clinical practice 2022; (187()):109875 doi:10.1016/j.diabres.2022.109875.

    PMID: 35472491
  15. 15

    GCK-MODY in the US National Monogenic Diabetes Registry: frequently misdiagnosed and unnecessarily treated.

    Carmody D, Naylor RN, Bell CD, et al.

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    PMID: 27106716
  16. 16

    A rare case of congenital hyperinsulinism (CHI) due to dual genetic aetiology involving HNF4A and ABCC8.

    Apperley L, Giri D, Houghton JAL, et al.

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    NGS Analysis Revealed Digenic Heterozygous GCK and HNF1A Variants in a Child with Mild Hyperglycemia: A Case Report.

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  19. 19

    Case Report: Identification of a HNF1A exons 1-10 heterozygous deletion in a Chinese MODY family.

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  20. 20

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    Two novel GCK mutations in Chinese patients with maturity-onset diabetes of the young.

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This page explains the diagnostic tests for MODY for educational purposes. Always consult your endocrinologist or a genetic counselor to interpret your lab results and determine the right testing strategy for you.

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