Key takeaways
- Tests are not a formality. They find conditions that change whether, and how, you should take medicine.
- A focused panel is usually enough. You do not need a 70-test package.
- Your history can rule out treatment even when every blood report is normal.
- Iron, B12 and vitamin D are worth checking because deficiencies are common in India and eating less can make them worse.
- Some tests are repeated during treatment, especially if you feel tired, dizzy or notice hair fall.
Why do you need tests at all?
Sometimes people say, "Doctor, I want to start this week. Can we skip the tests?" Okay, sure, let's start. Let's get your blood done first. It takes a day, not a month.
See, what happens is, GLP-1 medicines such as semaglutide and tirzepatide change how much you eat, how fast your stomach empties and how your body handles sugar. That is helpful, but it also means I need to know your starting point. Tests answer three questions:
- Is there a condition that makes medicine unsafe or needs a different plan? For example, undiagnosed diabetes, kidney problems or an underactive thyroid.
- Is there a deficiency we should correct first? Low iron, B12 or vitamin D can leave you tired and shedding hair once you start eating less.
- What does "better" look like for you? Your baseline HbA1c, cholesterol and liver numbers let you see health improvements, not just a lower number on the scale.
Which blood tests are usually checked?
The exact tests depend on your age, history and current medicines, but a typical starting panel looks like this:
| Test | What it tells us | Why it matters on weight loss medicine |
|---|---|---|
| HbA1c and fasting glucose | Average sugar over about three months | Picks up prediabetes or diabetes; diabetes medicines may need adjusting to avoid low sugars |
| Kidney function (creatinine, eGFR, electrolytes) | How well kidneys filter | Vomiting or diarrhoea can cause dehydration, which can strain the kidneys |
| Liver function tests | Liver health and bile flow | Fatty liver is common; also a baseline if gallbladder symptoms appear later |
| Lipid profile | Cholesterol and triglycerides | Shows heart risk and tracks improvement |
| TSH (with free T4 if needed) | Thyroid function | An underactive thyroid needs treating on its own; see thyroid and weight myths |
| Complete blood count | Haemoglobin, infection, platelets | Anaemia is common, especially in women |
| Iron studies or ferritin | Iron stores | Low iron adds to tiredness and hair fall |
| Vitamin B12 | Nerve and blood health | Common gap in vegetarians and in people on metformin |
| Vitamin D | Bone and muscle health | Commonly low in Indian adults, including in sunny Mumbai |
A pregnancy test is advised for women who could be pregnant. Pancreatic enzymes (lipase or amylase) are not usually routine at the start; they are checked if you develop persistent upper abdominal pain.
Which history questions matter more than blood tests?
Some reasons not to take GLP-1 medicines do not show up in any blood report. Your doctor should ask you directly about:
- Personal or family history of medullary thyroid cancer, or MEN 2 syndrome. These are reasons not to use semaglutide or tirzepatide.
- Past pancreatitis.
- Gallbladder disease or gallstones.
- Diabetic eye disease (retinopathy), if you have diabetes.
- Severe stomach problems such as gastroparesis.
- Pregnancy, breastfeeding or plans to conceive. Medicine is usually stopped about two months before trying for a baby.
- Eating disorders, current or past.
- All medicines you take, including insulin, sulfonylureas, contraceptive pills and ayurvedic or herbal products.
- Upcoming surgery, including dental procedures needing anaesthesia, because these medicines slow stomach emptying.
Please tell me about the ayurvedic tablets too. Everyone forgets those. More on this in who should not take weight loss injections.
Do you need an ECG, ultrasound or other scans?
Not routinely. An ECG may be advised if you are older, have chest symptoms, high blood pressure or diabetes. An abdominal ultrasound is useful if you have had gallbladder symptoms or if liver tests suggest significant fatty liver. A body composition measurement (with a scale or scan) is helpful to track muscle, but it is not a safety test.
That is very important to understand: more tests do not mean safer care. Targeted tests, read properly, are what keep you safe.
How should you prepare for the tests?
- Fast for 10 to 12 hours if fasting glucose and lipids are included. Water is fine.
- Take your usual medicines unless your doctor says otherwise. Mention if you take biotin supplements, which can affect some thyroid results.
- Go to an accredited lab. Most large labs in Thane, Mumbai and across India offer home collection.
- Keep all reports in one PDF so your doctor can compare them over time.
- Bring old reports. A rising HbA1c over three years tells a different story from a single value.
Which tests are repeated during treatment?
Repeat tests depend on how you are doing. Common reasons to recheck:
- HbA1c every three months or so if you have prediabetes or diabetes.
- Iron, B12 and vitamin D after the first few months of reduced eating, or earlier if you feel tired, dizzy or notice hair shedding (see hair fall during weight loss).
- Kidney function if you have had significant vomiting or diarrhoea.
- Liver tests and an ultrasound if you develop pain under the right ribs, especially after fatty meals, since rapid weight loss raises gallstone risk.
How I approach this at Dr Tvacha
In the Endgame Weight Programme, I review your history on the Rs 499 eligibility video consult and then ask only for the tests that apply to you. You can get them done at any lab near you, anywhere in India, and share the reports on WhatsApp. If the results or your history mean medicine is not right for you, I will say so plainly and suggest what to do instead. Details are on the weight loss page.
Frequently asked questions
Can I start weight loss medicine without blood tests?
I would not advise it. Blood tests can reveal undiagnosed diabetes, kidney problems, thyroid disease or deficiencies that change whether medicine is suitable and how the doses should be adjusted. A doctor who prescribes without any tests or history is skipping a basic safety step. Recent reports, usually from within the last three months, can often be reused.
Do I need a thyroid test before semaglutide or tirzepatide?
A TSH test is commonly done, because an underactive thyroid can cause tiredness and weight gain and should be treated on its own. But the more important thyroid question is your history. A personal or family history of medullary thyroid cancer or MEN 2 syndrome is a reason not to use these medicines, and no routine blood test detects that.
Why check vitamin B12 and vitamin D before weight loss medicine?
Both deficiencies are common in Indian adults, and B12 is especially low in many vegetarians and in people who take metformin. Once appetite falls, intake drops further. Low levels can cause fatigue, low mood, tingling and hair fall, which are easy to blame on the medicine. Correcting them early makes the whole process easier.
Are full-body health packages a good idea before starting?
Usually they are not necessary. Large packages add many tests that do not change the decision, and they can throw up borderline results that only cause worry. A focused panel chosen by the doctor who knows your history is more useful. If you already have a recent package report, share it, because it may cover most of what is needed.
How often will tests be repeated while on treatment?
It depends on your starting results. People with diabetes or prediabetes often recheck HbA1c every three months. Iron, B12 and vitamin D may be repeated after a few months of reduced eating, or earlier if symptoms appear. Kidney and liver tests are repeated if you have significant vomiting, diarrhoea or abdominal pain.
Written by
Dr Amit KarkhanisAesthetic Physician · MBBS, Dip. Dermatology (UK) · Reg. No. 2001/02/1124Founder of Dr Tvacha, practising in Thane since 2005. Leads the weight loss and hair programmes.
Sources
- Semaglutide injection (MedlinePlus, US National Library of Medicine)
- Monitoring patients on GLP-1 agonists (Australian Clinical Labs, Path Focus)
- Advice on metformin and reduced vitamin B12 levels (NHS North West London)
- Vitamin B12 deficiency in northern India tertiary care: prevalence, risk factors and clinical characteristics (PubMed)
- Prevalence and potential significance of vitamin D deficiency in Asian Indians (Indian Journal of Medical Research)
- FDA warns biotin may affect some lab test results (Lab Tests Online)
This article is for general education and does not replace a consultation. Medicines and treatments are prescribed only after a doctor's assessment. Last reviewed 25 October 2026.