Three blood tests appear often in conversations about metabolic health and cardiovascular risk. This guide explains what each one measures, why a clinician might order it, and what the results mean. These are not tests you order yourself. A clinician decides which tests make sense for you based on your history, your risk factors, and what they need to know to help you.
What is the A1C test and what does it show?
The A1C test measures the amount of hemoglobin with attached glucose and reflects your average blood glucose levels over the past 3 months [1]. Think of it as a three-month snapshot of how much glucose has been circulating in your blood.
A clinician may order an A1C test if you have risk factors for prediabetes or type 2 diabetes. The American Diabetes Association recommends testing in adults with a BMI of 25 or higher, or 23 or higher if you are of Asian ancestry, who also have one or more additional risk factors [2]. Those risk factors include a first-degree relative with diabetes, a history of cardiovascular disease, high blood pressure, abnormal cholesterol or triglyceride levels, polycystic ovary syndrome, or physical inactivity [2].
The A1C result falls into three bands [1]:
- Below 5.7% is normal
- 5.7% to 6.4% is prediabetes
- 6.5% or higher is diabetes
If your A1C lands in the prediabetes band, that does not mean you will develop type 2 diabetes. It means your blood glucose is higher than normal, and your risk is elevated. People with prediabetes have a high chance of developing type 2 diabetes within 5 to 10 years, but that timeline is not fixed. The Diabetes Prevention Program showed that losing 5% to 7% of body weight lowered the chance of developing type 2 diabetes. That is a concrete action that changes the trajectory.
For more on what an A1C of 5.7% specifically means and what to ask your clinician next, see A1C of 5.7, what it means.
What does an hs-CRP test measure?
An hs-CRP test measures very tiny increases in your C-reactive protein levels and is used to estimate your risk of heart disease [2]. C-reactive protein is a marker of inflammation in your body. When inflammation is present, your C-reactive protein level rises. The hs-CRP test is sensitive enough to catch very small increases that a standard CRP test would miss.
A clinician may order an hs-CRP test as part of a broader assessment of your cardiovascular risk. It is one tool among many. The test does not diagnose heart disease. It estimates risk by measuring a marker that correlates with cardiovascular events in population studies. Your clinician interprets the result alongside your other risk factors, your family history, your blood pressure, your cholesterol levels, and your lifestyle.
The hs-CRP test is not a routine screening test for everyone. It is ordered when a clinician is trying to refine their understanding of your cardiovascular risk, especially if your other risk factors are borderline or mixed.
Why might a clinician order a vitamin D test?
A vitamin D test measures the levels of vitamin D in your blood, and most tests measure 25(OH)D, which is the most accurate way to see if you have enough vitamin D [3]. Vitamin D is made in your skin when it is exposed to sunlight, and it is also found in some foods and in fortified milk.
A clinician may order a vitamin D test if you have limited sun exposure because you stay indoors, cover up outside, use sunscreen, or live where there is little sunlight [3]. Vitamin D deficiency is common in people with limited sun exposure, and it is particularly common in South Asian populations. In a UK study of 6,433 South Asian adults aged 40 to 69, 92% had vitamin D levels below 50 nmol/L, a threshold often used to define insufficiency [4]. That is UK data, not US data, but it illustrates why a clinician might be more likely to check vitamin D in a South Asian patient.
Vitamin D plays a role in bone health, immune function, and inflammation. Low vitamin D has been associated with increased risk for several conditions, including type 2 diabetes and cardiovascular disease. If your test shows low vitamin D, your clinician will discuss whether treatment makes sense for you. The decision depends on your individual risk factors and your clinician's judgment.
For more on vitamin D and South Asian adults, see vitamin D and South Asian adults.
When do these tests make sense?
The American Diabetes Association recommends screening for prediabetes and type 2 diabetes in adults with overweight or obesity (BMI 25 or higher, or 23 or higher for people of Asian ancestry) who have one or more additional risk factors [2]. The CDC lists those risk factors: being age 45 or older, having a parent or sibling with type 2 diabetes, being physically active less than 3 times a week, having non-alcoholic fatty liver disease, having had gestational diabetes or having given birth to a baby who weighed over 9 pounds, and being an African American, Hispanic or Latino, American Indian or Alaska Native person, with the CDC adding that some Pacific Islander people and Asian American people also have higher risk [1].
Most people with prediabetes have no symptoms. About 115 million US adults have prediabetes, and most of them do not know [1]. That is why screening matters: you cannot act on information you do not have.
An hs-CRP test is not a routine screening test. It is ordered when a clinician is refining a cardiovascular risk assessment and needs more information.
A vitamin D test is ordered when a clinician suspects deficiency based on your history and risk factors, or when vitamin D status is relevant to another condition they are evaluating.
The three tests at a glance
Here are the tests this guide covers, what each one measures, and why a clinician may order it:
| Test | What it measures | Why a clinician may order it |
|---|---|---|
| A1C | Average blood glucose over the past 3 months [1] | Screening for prediabetes or type 2 diabetes in adults with overweight or obesity and additional risk factors [2] |
| hs-CRP | Very tiny increases in C-reactive protein levels [2] | Estimating cardiovascular risk as part of a broader risk assessment [2] |
| Vitamin D | Levels of 25(OH)D in your blood [3] | Limited sun exposure, or when vitamin D status is relevant to another condition being evaluated [3] |
What these tests do not do
These three tests are tools, not diagnoses. An A1C in the prediabetes band does not mean you will develop diabetes. An elevated hs-CRP does not mean you will have a heart attack. A low vitamin D does not mean you are sick. Each result is one piece of information that a clinician uses to understand your risk and to decide what to do next.
These tests also do not replace a conversation with your clinician. The numbers are part of a larger picture that includes your family history, your lifestyle, your other health conditions, and your goals. A clinician who knows your full story can interpret these results in context and help you decide what makes sense for you.
What to do next
- Ask your clinician whether screening for prediabetes makes sense for you based on your BMI and your risk factors.
- If you have not had an A1C test recently and you have risk factors for prediabetes, ask your clinician to order one.
- Write down your A1C result, the date it was measured, and what your clinician said it means. Bring this to your next appointment.
- If your clinician mentions an hs-CRP test or a vitamin D test, ask why they think it is relevant to your care and what they will do with the result.
- Visit the Sehat guides hub to read more about specific test results and what they mean for your next steps.
- If you have questions about a result you received, ask your clinician to explain it. Do not rely on online sources alone to interpret your own blood work.
Sources
- NIDDK, the A1C test, A1C ranges and prediabetes definition, accessed 2026-08-06, https://www.niddk.nih.gov/health-information/diagnostic-tests/a1c-test
- American Diabetes Association, Diagnosis and Classification of Diabetes, Standards of Care in Diabetes 2026, screening recommendations and A1C cut points, accessed 2026-08-06, https://diabetesjournals.org/care/article/49/Supplement_1/S27/163926/2-Diagnosis-and-Classification-of-Diabetes
- MedlinePlus, vitamin D test, what the test measures and reasons for ordering, accessed 2026-08-06, https://medlineplus.gov/lab-tests/vitamin-d-test/
- Darling and colleagues, vitamin D deficiency in UK South Asian adults, PubMed Central, vitamin D levels in UK South Asian populations, accessed 2026-08-06, https://pmc.ncbi.nlm.nih.gov/articles/PMC7844605/