CardioIQ^® Insulin Resistance Panel With Score

Insulin resistance (IR) is a metabolic condition that occurs when cells become less sensitive to insulin’s stimulation to absorb glucose from the bloodstream. When cells become insulin resistant, pancreatic β-cells increase the production of insulin to overcome IR and maintain normoglycemia.^1,2 Over time, IR may continue to increase and/or pancreatic function may decline,² allowing blood glucose and HbA1c levels to elevate. This can be a gradual process and makes early identification of IR difficult.

If IR is left untreated, it can lead to development of prediabetes and type 2 diabetes mellitus (T2DM). It is also associated with other clinical conditions including hypertension, cardiovascular disease, stroke, nonalcoholic fatty liver disease (NAFLD), polycystic ovary syndrome, and certain forms of cancer.¹ Therefore, early identification of IR and intervention can halt or reverse progression of clinical conditions.

The CardioIQ^® Insulin Resistance Panel With Score estimates the probability that an individual currently has insulin resistence (IR). It is based on laboratory test measurements of insulin and C-peptide, which are used in a calculation to provide a score that indicates the probability of the individual having IR.³

Although insulin and C-peptide are co-secreted from pancreatic β-cells at the same rate, their stability and clearance vary: C-peptide has much longer half-life in circulation (20-30 minutes for C-peptide compared to 3-5 minutes for insulin), and insulin is primarily cleared by the liver, whereas C-peptide is cleared through the kidneys.⁴ Together, insulin and C-peptide measurements provide a better indicator of IR than either alone.³

The score calculation using insulin (pmol/L) and C-peptide (pmol/L) via tandem mass spectrometry (LC/MS/MS) is³:

The insulin suppression test⁵ and euglycemic clamp⁶ are standards for assessing insulin resistance (IR). However, these methods are not well-suited for primary care clinics: they are time-consuming and labor-intensive, and require intravenous infusion. Fasting insulin and the homeostatic model assessment of IR (HOMA-IR), a score of IR based on fasting glucose and insulin measurements, are simple methods that can indicate IR.

In a study of apparently healthy individuals assessed for IR by the insulin suppression test, the insulin and C-peptide score outperformed insulin and the HOMA-IR. The odds ratio (OR) comparing the top quartile of those with IR vs no IR was 6.9 for the IR score, 1.6 for insulin alone, and 1.5 for the HOMA-IR.³

No. The insulin and C-peptide values used in the calculation are measured simultaneously by mass spectrometry (LC/MS/MS) methodology from a single sample.⁷ C-peptide cannot be ordered separately using this methodology, and C-peptide (test code 372) by immunoassay is not an equivalent test and cannot be used in the calculation of the score. The panel component Insulin, Intact, LC/MS/MS (test code 93103) can be ordered separately.

The CardioIQ^® Insulin Resistance Panel with Score will aid in early identification of insulin resistance (IR). Testing is appropriate for individuals:

• At risk for IR, prediabetes, or T2DM
• Who are overweight/obese
• Who have a family history of T2DM
• Who have a history of gestational diabetes mellitus
• Who meet the criteria for metabolic syndrome
• Who have clinical features of IR including:
  • Hypertension
  • Central obesity
  • Acanthosis nigricans (dark patches of thick, velvety skin on the back of the neck, armpits and groin)

The CardioIQ^® Insulin Resistance Panel With Score provides a calculated score based on the insulin and C-peptide values (see Question 2). Each score is associated with a probability of IR based on population tertiles.³

A score less than 33 is optimal and indicates normal insulin sensitivity.

A score of 33 to 66 indicates an individual has >4-fold greater probability of having IR relative to someone with a score less than 33.  

A score of greater than 66 indicates an individual has >15-fold greater probability of having IR relative to someone with a score less than 33.  

For patients without known diabetes, a fasting insulin level >10 µU/mL is consistent with the presence of hepatic steatosis.⁸ Consider further evaluation to assess the presence and stage of nonalcoholic fatty liver disease (NAFLD). For additional information on intact insulin, please refer to Education.QuestDiagnostics.com/faq/FAQ170. 

While both these tests identify metabolic risk, they differ in other clinical aspects: the disease state identified, timing of risk, and panel components. The Insulin Resistance Panel With Score provides a value that indicates the likelihood an individual currently has IR using insulin and C-peptide, whereas the Diabetes Risk Panel with Score assesses an individual’s probability of developing diabetes in the next 8 years.

C-peptide is renally cleared; therefore, those with reduced kidney function may have an increased amount of C-peptide, which may affect the Insulin Resistance Score. While kidney function has been associated with risk of IR,^3,9 this test has not been validated for use in individuals with reduced kidney function; results in this population should be interpreted with caution. 

Insulin analogs lispro and glargine interfere with insulin quantitation, while insulin analogs aspart and degludec do not. The presence of insulin antibodies may cause an artificially low result.