Understanding blood tests: insulin resistance, thyroid and metabolic health

Common tests and uses for weight loss

The following are items that may appear on the report,A checklist that not everyone must do. The doctor will make arrangements based on medical history, symptoms, current medications and existing results.

What is the difference between fasting blood glucose and HbA1c?

Fasting blood glucose reflects the condition at the time of blood draw, which may be affected by fasting time, stress, or illness; glycated hemoglobin (HbA1c) roughly reflects the average blood glucose in the past 2–3 months. Anemia or some hemoglobin abnormalities may affect the accuracy of HbA1c, and doctors will make judgments based on other data.

If results are inconsistent with symptoms or risks, the physician may order repeat testing or, if appropriate, perform an oral glucose tolerance test (OGTT). Whether you have prediabetes or diabetes should be determined according to the applicable diagnostic criteria and confirmation process.

Data basis:NIDDK: Insulin resistance, prediabetes and blood glucose testing。

Insulin resistance: Fasting insulin vs. HOMA-IR What to look at?

Insulin resistance is the body's poor response to insulin; in the early stages, more insulin may need to be secreted to maintain blood sugar within the normal range. Therefore, normoglycemia does not necessarily mean the complete absence of insulin resistance.

Fasting insulinshould be read together with the same blood sugar, medical history and medication; some reports will provide HOMA-IR, which is an index to estimate insulin resistance using fasting insulin and fasting blood glucose. It is not a direct measurement, and different groups and testing methods may have different criteria. You cannot just use a number on the Internet to judge.

Physicians will decide whether to arrange testing based on metabolic risk and purpose of testing. Not every bariatric patient needs testing. HOMA-IR cannot alone diagnose diabetes, guarantee weight loss, or be used to determine Mounjaro dosage; if insulin is already used, confirm whether such estimates are applicable.

Data basis:NIDDK: Insulin resistance, prediabetes and blood glucose testing；MedlinePlus: Blood insulin test。

Thyroid function: relationship between TSH, Free T4 and body weight

Thyroid function affects how the body uses energy. When evaluating, it is usually first to look at TSH (thyroid stimulating hormone); If the results are abnormal or there are clinical doubts, then use Free T4/FT4 (free thyroxine). Testing for T3 or thyroid antibodies is only done when necessary, and a full set of tests is not required every time.

High TSH and low Free T4 may point to primary hypothyroidism; other combinations require further interpretation. There are many reasons for weight gain. Just because you can't lose weight, you shouldn't assume it's your thyroid, and you shouldn't self-medicate just because of a slight TSH abnormality.

If you are taking biotin (commonly found in hair or nail supplements), thyroid medication, or are pregnant, please inform us in advance. Biotin may interfere with some tests. Whether to suspend and for how long should be determined by the physician or testing unit. When your thyroid function is normal, you should not self-administer thyroxine for weight loss.

Data basis:American Thyroid Association: Thyroid function testing；American Thyroid Association: Thyroid and Weight。

Blood lipids: LDL, HDL and triglycerides

Blood lipids include total cholesterol, LDL, HDL and triglycerides (TG). LDL has been linked to atherosclerosis risk; triglycerides are also worth tracking during weight management.

Treatment goals will be adjusted based on whether there is diabetes, cardiovascular disease and other risks. You cannot just look at whether there is a red letter in the report. Just because the numbers have improved after losing weight does not mean that you can stop taking the blood-lipid-lowering drugs on your own.

Data basis:MedlinePlus: Blood lipid test。

Liver index: AST, ALT and fatty liver

AST, ALT provide clues to liver cell damage, but are not the whole story of liver health. A high level may be related to a variety of conditions; a normal level cannot directly rule out fatty liver.

Physicians will order ultrasound or other liver assessments as needed based on alcohol use, medication use, hepatitis, and metabolic risks. Bringing previous results with you when tracking is more helpful than just looking at a certain number.

Data basis:MedlinePlus: Liver function tests。

Kidney function and electrolytes: dehydration and medication may affect

Creatinine and eGFRAssists in the assessment of kidney filtration capacity. eGFR is an estimate and is also affected by factors such as muscle mass. A single low eGFR does not necessarily mean chronic kidney disease. If you are at risk for diabetes or other kidney disease, your doctor may also arrangeUrinary albumin/creatinine ratio (UACR); This is a urine test, not a blood test.

Electrolytes such as sodium and potassiumRelated to water balance, muscle and heart function. If you have repeated vomiting, diarrhea, eat very little, or use drugs that may affect water and electrolytes, the doctor will arrange tests as appropriate. If the urine output is significantly reduced, you are about to faint, or you cannot drink water, you should seek medical treatment directly.

Data basis:NIDDK: Kidney function and urine albumin test；MedlinePlus: Electrolyte Testing。

Uric acid: If you have a history of gout or stones, you should be evaluated together

Uric acid (UA) is a product of the body's metabolism of purin and is mainly excreted through the kidneys. If you have gout, uric acid stones, metabolic syndrome or related medications, you can discuss with your doctor whether testing and tracking are needed.

High uric acid does not mean that you have gout, nor is it an indicator of "fat burning speed". Whether treatment is needed depends on symptoms, medical history and kidney function, and is not determined by a single number.

Data basis:MedlinePlus: Uric acid test。

Anemia and Nutrition: CBC, Ferritin, B12, and Vitamin D

During the weight loss period, if you have been eating less for a long time, are obviously tired, or have dietary restrictions, you can tell the medical team about the situation and choose examinations based on clues:

• Complete blood count (CBC):Contains hemoglobin and other information to help understand whether there is anemia and other blood cell abnormalities.
• Ferritin:Helps evaluate iron storage; when menstrual flow is heavy, iron deficiency or malabsorption is suspected, it may be combined with other iron-related tests. Ferritin is also affected by inflammation and cannot be determined by looking at just one item.
• Vitamin B12:Conditions such as a vegan diet, gastrointestinal surgery, or absorption problems, as well as metformin use, may require testing based on risk and symptom assessment.
• 25-OH Vitamin D:Used to assess vitamin D status; whether measurement is needed depends on clinical issues such as hypocalcemia, bone, or resorption. Generally, healthy adults who are not obese must undergo routine examinations.

These examinations are to identify problems that may affect health and physical strength. They are not a "complete weight loss package" that every patient needs, nor can it be inferred that supplementing with health supplements will definitely lead to faster weight loss.

Data basis:MedlinePlus: Complete Blood Count；MedlinePlus: Ferritin test；NIH: Vitamin B12 and diet and medication；Endocrine Society: Vitamin D testing guidelines (2024)。

Other hormones: Check again when there are related symptoms

Testing will only be ordered if the history, physical examination, or symptoms lead the physician to suspect an endocrine disorder. Taking Cushing's disease as an example, it is not recommended to screen all overweight people extensively; nor can a random blood draw of cortisol be used to determine "stress obesity" or rule out Cushing's disease.

There are different rules for whether to examine, when to draw blood, and whether urine, saliva, or inhibition testing is required, and the choice should be made by the physician based on clinical concerns.

Data basis:Endocrine Society: Cushing's Disease Testing Guidelines。

Prepare these four things before blood drawing and during follow-up visits

1. First confirm the fasting requirements:Fasting blood glucose and fasting insulin usually require fasting according to the testing unit's instructions; HbA1c itself does not require fasting, but other items at the same time may require fasting.
2. List drugs and health products:Includes insulin, hypoglycemic drugs, thyroid drugs, biotin and steroids. Do not stop taking medication on your own, but first confirm your medication schedule on the day of blood draw.
3. Bring the previous report:Together with changes in weight, waist circumference, diet and activity, and indicate any recent illness, vomiting, diarrhea or significant decrease in food intake.
4. Confirm tracking purpose:What questions will this examination answer? Will the results change treatment? When is retesting required? The frequency of different items should be arranged according to the disease condition.

Different testing methods, units, ages or physiological conditions may have different reference ranges. Please refer to the report and physician's interpretation; a single red letter does not represent a complete diagnosis, and everything that is normal does not mean that all diseases have been ruled out.