Which blood tests to get before weight loss
A weight-loss blood test has two jobs: find conditions that change the plan (prediabetes, fatty liver, thyroid disease, kidney problems) and set a baseline so you can see what the weight loss is doing inside, not just on the scale. The markers below cover both.
| Marker | Why it matters | What a result suggests | On SiPhox |
|---|---|---|---|
| HbA1c | Screens for prediabetes and diabetes, which change the plan | 5.7% to 6.4% is prediabetes; 6.5% or more is the diabetes range | Longevity, Heart & Metabolic, Ultimate 360, GLP |
| Fasting insulin or C-peptide | Show insulin resistance before A1C rises | High values fit insulin resistance | C-peptide: Longevity, Heart & Metabolic, Ultimate 360, GLP. Fasting insulin: not on SiPhox |
| Triglycerides and HDL | Usually the first lipids to improve | High TG and low HDL fit insulin resistance | Longevity, Heart & Metabolic, Thyroid Focus, Ultimate 360, GLP |
| ApoB and LDL | Heart risk baseline | LDL often changes less with weight loss than TG and HDL | Longevity, Heart & Metabolic, Ultimate 360, GLP |
| ALT, AST, GGT | Fatty liver is common with excess weight | Raised ALT often falls as liver fat drops | Heart & Metabolic, Thyroid Focus, Ultimate 360, GLP |
| TSH | Rules out hypothyroidism | High TSH needs free T4 and a doctor; it rarely explains much weight | Longevity, Heart & Metabolic, Thyroid Focus, Ultimate 360, GLP |
| Creatinine and eGFR | Kidney baseline before high-protein diets or medication | eGFR under 60 changes medication and diet choices | Heart & Metabolic, Thyroid Focus, Ultimate 360, GLP |
| Ferritin, B12, vitamin D | Eating less can mean fewer nutrients | Low baseline values should be corrected early | Ferritin: Longevity, Thyroid Focus, Ultimate 360, GLP. B12: Ultimate 360, GLP |
| hs-CRP | Low-grade inflammation tracks body fat | Usually falls with weight loss | Longevity, Heart & Metabolic, Thyroid Focus, Ultimate 360, GLP |
| Testosterone and SHBG (men) | Excess weight lowers both | Often rise as weight comes down | Longevity (men), Thyroid Focus, Hormone Focus, Ultimate 360, GLP |
Can a blood test explain weight gain?
Occasionally, and less often than people hope. The American Thyroid Association says about 5 to 10 pounds of weight gain may be thyroid-related, depending on how severe the hypothyroidism is, and that treatment returns weight to where it was before the thyroid problem started. So a high TSH is worth finding, but it rarely explains 30 or 40 pounds. Our hypothyroidism blood test guide covers the thyroid workup.
Other hormonal causes, such as Cushing's syndrome, are rare and need specific timed tests ordered by a doctor; a single morning cortisol on a home panel cannot diagnose or rule them out. Women with irregular periods and weight gain should read our PCOS blood test guide, because insulin resistance in PCOS changes which approaches work best. Medicines, sleep and stress are more common drivers than any blood result.
Which numbers improve, and how fast
Source: Wing et al., Diabetes Care 2011 (Look AHEAD, 5,145 adults with type 2 diabetes), odds ratios versus weight-stable participants at 1 year.
In the Look AHEAD trial of 5,145 adults with type 2 diabetes, losing 5% to under 10% of body weight in a year was linked with better A1C, blood pressure, triglycerides and HDL, but not with LDL. People who lost 10% to 15% did better still. That pattern matches what most people see: triglycerides, A1C and ALT move first, and LDL may barely change.
| Marker | When to recheck | Why |
|---|---|---|
| Triglycerides, ALT | 6 to 12 weeks | Respond quickly to diet change and liver fat loss |
| HbA1c | About 3 months | Reflects roughly the last three months of blood sugar |
| ApoB, LDL, HDL | 3 to 6 months | Slower, and LDL may not fall |
| Ferritin, B12, vitamin D | 3 to 6 months | Catch nutrient drops from eating less |
Worked example: 16 pounds in six months
Illustrative numbers. A 52-year-old woman weighing 210 lb aims to lose 5% to 10% (10.5 to 21 lb). She tests at the start and again after losing 16 lb (7.6%) at six months:
| Marker | Baseline | Month 6 |
|---|---|---|
| HbA1c | 6.0% | 5.7% |
| Triglycerides | 210 mg/dL | 150 mg/dL |
| HDL | 42 mg/dL | 46 mg/dL |
| ALT | 41 U/L | 28 U/L |
| LDL | 138 mg/dL | 134 mg/dL |
The direction matches Look AHEAD: A1C, triglycerides and ALT improve, HDL edges up, LDL barely moves. Her A1C is now at the top of the normal range rather than in prediabetes. Seeing that on paper is often what keeps people going through the slow months. Three tests (baseline, 3 and 6 months) on Heart & Metabolic cost $447 with shipping.
How to prepare so results are comparable
- Test the same way every time: same time of day, and either always fasting or always not. HbA1c does not need fasting, but triglycerides move after a meal.
- Avoid testing during a cold or after a hard workout, which raise hs-CRP and liver enzymes.
- Hydrate normally. Dehydration concentrates creatinine and hemoglobin, and for an at-home draw it makes the device harder to fill.
- List supplements and medicines, especially iron, B12, vitamin D and biotin, which change or interfere with results.
If you use weight-loss medication
NIDDK lists several prescription medicines for weight management, and GLP-1 medicines in particular change what to monitor: kidney function when stomach side effects cause dehydration, and nutrients such as iron, B12 and vitamin D when intake drops sharply. We cover that schedule in detail in our GLP-1 blood test guide. SiPhox's GLP Optimization panel ($199 plus shipping) adds iron studies, B12, folate and vitamin D to the metabolic, liver and kidney markers. Your prescriber sets the testing schedule.
What an at-home test can and cannot do for weight loss
- Set a baseline of blood sugar, lipids, liver, kidney and thyroid before you start
- Show the inside changes every 3 months, even when the scale stalls
- Catch nutrient drops from eating less
- Diagnose anything: a diagnosis needs a clinician
- Measure body fat, muscle or blood pressure
- Test fasting insulin or glucose on SiPhox EasyDraw panels, or rule out rare hormonal causes
Best-fit SiPhox panel for weight loss
| If you want | Test | Choose |
|---|---|---|
| A baseline and progress checks | HbA1c, C-peptide, lipids, ApoB, ALT, AST, eGFR, TSH, hs-CRP | Heart & Metabolic |
| The same plus hormones and vitamin D | HbA1c, ApoB, Lp(a), hs-CRP, vitamin D, ferritin, testosterone or female hormones | Longevity Essentials |
| Monitoring on GLP-1 medication | Metabolic, liver, kidney, iron, B12, folate, vitamin D | GLP Optimization |
| Fasting insulin, body composition or rare hormone tests | Venous lab, DEXA, timed tests | Your doctor |
Heart & Metabolic at $124 plus $25 shipping covers the markers that change most with weight loss, including the liver enzymes most general panels skip. For blood sugar in depth, see our prediabetes blood test guide.
Heart & Metabolic
Lipids plus kidney and liver function: the panel for cardiovascular and metabolic risk.
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Longevity Essentials
The default panel: heart, metabolic, hormone and inflammation markers in one draw.
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Built for people on GLP-1 medication: metabolic, liver, kidney, nutrient and iron markers.
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Frequently asked questions
What blood tests should I get before losing weight?
HbA1c, a lipid panel or ApoB, liver enzymes (ALT and AST), TSH, creatinine and eGFR, and nutrients such as ferritin, B12 and vitamin D. Add fasting insulin if your doctor wants a measure of insulin resistance.
Can a blood test tell why I cannot lose weight?
Sometimes it finds a contributor, such as hypothyroidism, insulin resistance or PCOS. The ATA says hypothyroidism typically explains about 5 to 10 pounds, so most weight gain has other causes.
Which blood results improve first with weight loss?
Triglycerides and ALT often improve within weeks, HbA1c over about three months. In Look AHEAD, 5% to 10% weight loss improved A1C, triglycerides and HDL, but not LDL.
How often should I get blood work while losing weight?
A baseline, then about every three months while actively losing weight, then once or twice a year when stable. On weight-loss medication, follow your prescriber's schedule.
Do I need different blood tests on GLP-1 medication?
Yes, kidney function and nutrients such as iron, B12, folate and vitamin D matter more. See our GLP-1 blood test guide for the full schedule.
Sources
- Wing RR et al. Benefits of modest weight loss in improving cardiovascular risk factors (Look AHEAD). Diabetes Care 2011
- American Thyroid Association: Thyroid and weight
- NIDDK (NIH): Diabetes tests and diagnosis
- NIDDK (NIH): The A1C test and diabetes
- NIDDK (NIH): Prescription medications to treat overweight and obesity
- MedlinePlus: Liver function tests
- MedlinePlus: Cholesterol levels
- MedlinePlus: Insulin in blood
- National Kidney Foundation: Estimated glomerular filtration rate (eGFR)
- MedlinePlus: Cortisol test
- SiPhox Health: Heart & Metabolic panel (checked 29 Sep 2026)
- SiPhox Health: Longevity Essentials panel and add-ons (checked 29 Sep 2026)
- SiPhox Health: GLP Optimization panel (checked 29 Sep 2026)