Tirzepatide labs: what to test before, during, and after

The standard tirzepatide prescribing workflow includes minimal labs. Some clinics order a baseline HbA1c and lipid panel; some don't order anything. The reasoning is reasonable: if you're tolerating the drug and progressing on weight loss, the labs are mostly informational.

The reasoning misses a few things that are worth catching, especially for patients who plan to be on the drug for 12+ months. Here's the panel that's worth requesting even when your prescriber doesn't volunteer it.

Baseline labs (before starting or in week 1-2)

The minimum useful panel:

HbA1c. Marker for chronic glucose control. Useful even in non-diabetics as a metabolic baseline; meaningful in diabetics as the primary efficacy endpoint.

Fasting glucose. Basic metabolic state.

Lipid panel. Total cholesterol, LDL, HDL, triglycerides. The triglyceride number is the most likely to shift on tirzepatide and the most clinically meaningful change for cardiometabolic risk.

Basic metabolic panel. Sodium, potassium, chloride, bicarbonate, BUN, creatinine, eGFR. Establishes kidney function baseline; relevant if you're going to be in a meaningful caloric deficit.

TSH. Thyroid function baseline. Rapid weight loss can affect thyroid hormone needs in patients with existing thyroid disease, and changes are easier to interpret with a baseline.

Liver enzymes (AST, ALT, GGT). Baseline hepatic function. NAFLD/MASH improvement is one of the documented benefits of GLP-1s; tracking liver enzymes lets you measure that.

Vitamin D and B12. Often surprisingly low at baseline in patients about to start a calorie deficit. Replacing both is cheap and improves how the deficit feels.

This panel runs about $80-200 in the US depending on insurance and lab, often free under most insurance plans, and 1,500-3,000 THB in Bangkok if you're paying out of pocket.

What's optional but useful at baseline

Calcitonin. Marker for medullary thyroid carcinoma (the cancer the boxed warning is about). If you have any family history of thyroid disease, baseline calcitonin gives you a reference point. Normal value is reassuring; a normal-then-rising trajectory would be the signal worth investigating.

Inflammatory markers (hs-CRP, ESR). Useful for tracking the inflammatory-improvement story over time. GLP-1s reduce systemic inflammation; quantifying that gives you another data point beyond weight.

Insulin and HOMA-IR. Direct measure of insulin sensitivity. More informative than fasting glucose for non-diabetic patients; gives a clearer picture of metabolic state.

Ferritin. Iron stores. Patients losing weight rapidly can deplete iron stores; replacing matters for energy and lifting performance.

Body composition baseline. Discussed in DEXA on tirzepatide; not a blood test but a useful baseline for tracking lean mass.

These add 80-200 USD or 1,500-3,000 THB on top of the basic panel, depending on lab.

Month 3 panel (the first checkpoint)

If everything is going well at month 3, the minimum panel:

• HbA1c (especially in diabetics)
• Lipid panel (looking for triglyceride drop)
• Basic metabolic panel (kidney function check)

If something is concerning at month 3:

• Add liver enzymes if abdominal symptoms or unusual fatigue
• Add TSH if you have a thyroid history and energy is off
• Add ferritin if fatigue is the dominant symptom

The month 3 panel is partly to confirm things are working metabolically (HbA1c falling, triglycerides falling, kidney function stable) and partly to catch the rare case where something is off.

Month 6 panel (the substantive one)

By month six, real metabolic shifts have occurred. The panel that tells the full story:

• HbA1c (now meaningfully different from baseline in most patients)
• Full lipid panel
• Basic metabolic panel
• Liver enzymes (NAFLD improvement is often visible by now)
• TSH (thyroid hormone needs may have shifted)
• Vitamin D and B12 (deficiency is common at month six even in patients who started replete)
• Ferritin (worth checking again)

Optional but useful at month six:

• DEXA body composition (see the dedicated post)
• Insulin and HOMA-IR (the insulin sensitivity improvement is the long-term metabolic story)

The month six panel is also when most prescribers will discuss whether you're at maintenance dose, whether to step up further, and whether to consider tapering eventually.

Month 12 and annual labs

By the one-year mark, the basic metabolic shifts have stabilized for most patients. The annual panel:

• HbA1c
• Lipid panel
• Basic metabolic panel
• Liver enzymes
• TSH
• Vitamin D and B12

Plus a body composition scan if you've been doing them at 6-month intervals. By month 12 the trajectory is mostly set; quarterly scans become overkill.

For patients on long-term maintenance dosing (year 2 onwards), an annual panel is reasonable. The drug effects have stabilized; you're mostly monitoring for slow drift in metabolic markers.

When to escalate

A few specific lab abnormalities are worth investigating actively rather than monitoring:

HbA1c rising during treatment. Should not happen on an effective GLP-1. If your HbA1c is trending up at month 6, the drug isn't doing what it should and the regimen needs review.

Liver enzymes elevated 2-3x above baseline. Possible drug-induced hepatotoxicity (rare for tirzepatide), or worsening NAFLD that's not responding to the drug, or unrelated. Worth a workup.

eGFR declining meaningfully. Kidney function changes can occur with rapid weight loss and dehydration. A 10-15 point drop is worth investigating; a 30+ point drop is acute and requires immediate clinical attention.

Ferritin under 30 with fatigue. Replace with oral iron or, in severe cases, IV iron. The improvement in energy after iron replacement is often the single most noticeable change patients describe.

TSH significantly off baseline. Adjust thyroid medication if you're on it; investigate if you're not.

What I'd actually request

If your prescriber doesn't volunteer labs, ask explicitly for:

1. Baseline labs in the first two weeks (the basic panel above) 2. A month 6 panel that includes liver enzymes and TSH alongside the basic markers 3. Annual labs at month 12 and yearly thereafter

Most prescribers will agree once you ask. The friction is rarely the request itself; it's that the request often doesn't get made.

For patients in regions where labs are inexpensive (Thailand, parts of Asia), running this panel quarterly through year one is reasonable and doesn't strain the budget. For patients in regions where labs are expensive (US private market, parts of Europe), the 0/3/6/12-month cadence is the cost-conscious version that still catches what matters.