Retatrutide is the first triple-hormone-receptor agonist ever developed — a once-weekly injection that simultaneously activates GLP-1, GIP, and glucagon receptors. In Phase 2 trials published in the New England Journal of Medicine, participants lost up to 24.2% of their body weight in 48 weeks. In Phase 3, the TRIUMPH-4 trial reported average weight loss of 28.7% (roughly 5 stone) at 68 weeks — more than any other obesity medication ever tested.
But retatrutide does not just change the number on the scale. Its unique triple-receptor mechanism triggers sweeping metabolic changes across your liver, kidneys, thyroid, pancreas, lipids, blood sugar, and nutritional stores. These changes are overwhelmingly beneficial — but they require monitoring. Without baseline blood tests and regular follow-up panels, neither you nor your prescriber can distinguish between expected improvements, harmless fluctuations, and genuine warning signs.
This guide covers the 15 essential biomarkers you should monitor on retatrutide, based on data from the TRIUMPH clinical trial programme, published Phase 2 safety results, and established monitoring protocols for GLP-1-class medications. It includes specific target ranges, a monitoring schedule from baseline through 12 months, red flags that require immediate attention, and how to access these tests in the UK.
Key Takeaways
- Baseline blood tests before starting retatrutide are essential — they create the reference point against which every future result is compared. Without them, monitoring is guesswork.
- Retatrutide's triple-receptor mechanism (GLP-1 + GIP + glucagon) affects more organ systems than single or dual agonists, requiring broader monitoring.
- The 15 essential biomarkers span six panels: metabolic, liver, kidney, thyroid, lipid, pancreatic, nutritional, and inflammatory.
- Liver monitoring is especially important — retatrutide reduced liver fat by up to 86% in trials, but transient ALT elevations above 3x the upper limit occurred in 1% of participants.
- Test at baseline, 3 months, 6 months, and 12 months — with ad hoc kidney function tests if you experience significant GI side effects.
- The Peak Insights 70 blood test covers all 15 biomarkers in a single panel, while the Core Health 45 covers the most critical markers at a lower price point.
Why Blood Tests Matter for Retatrutide
Every GLP-1-class medication requires blood test monitoring. But retatrutide demands a broader panel than semaglutide (Wegovy/Ozempic) or tirzepatide (Mounjaro/Zepbound) because it targets an additional receptor — glucagon — that the others do not.
The glucagon receptor is responsible for retatrutide's extraordinary effects on liver fat (up to 86% reduction in trials), increased energy expenditure, and enhanced fat oxidation. But glucagon activation also increases hepatic glucose output, stimulates amino acid catabolism, and places additional metabolic demands on the liver and kidneys. This means monitoring requirements are broader, not narrower, than for existing obesity medications.
Here is what retatrutide does to your body that blood tests can track:
- Metabolic control: HbA1c and fasting glucose improve significantly. In the Phase 2 trial, HbA1c reductions were dose-dependent and clinically meaningful even in non-diabetic participants.
- Liver enzymes: Mean ALT and AST levels decreased or remained stable at 48 weeks. However, transient ALT elevations exceeding 3x the upper limit of normal occurred in approximately 1% of participants — making baseline liver function essential.
- Liver fat: The Phase 2a MASLD trial published in Nature Medicine showed 86% of participants on the 12 mg dose achieved normal liver fat levels (<5%) at 24 weeks. Biomarkers of liver fibrosis (K-18, pro-C3) also improved significantly.
- Kidney function: Dehydration from GI side effects (nausea, vomiting, diarrhoea) can temporarily impair kidney function. Creatinine and eGFR monitoring catches this early.
- Thyroid: Like all GLP-1-class drugs, retatrutide carries a precautionary warning regarding thyroid C-cell tumours observed in rodent studies. TSH monitoring is a standard safety measure.
- Lipids: TRIUMPH-4 showed clinically meaningful improvements in non-HDL cholesterol, triglycerides, and high-sensitivity CRP — key cardiovascular risk markers.
- Pancreatic enzymes: Asymptomatic lipase and amylase elevations were observed in trials, with one case of acute pancreatitis reported. Baseline values allow comparison if abdominal symptoms develop.
- Nutritional status: Reduced food intake from appetite suppression can deplete iron, vitamin B12, vitamin D, and other micronutrients within months.
Blood tests transform subjective symptoms into objective data. They allow your prescriber to confidently escalate doses, hold treatment if needed, or add supplementation — all based on evidence rather than guesswork.
The 15 Essential Biomarkers to Monitor on Retatrutide
The following panel is based on safety endpoints measured in the TRIUMPH clinical trial programme, the Phase 2 trial published in the NEJM, the Phase 2a MASLD trial in Nature Medicine, and established GLP-1 monitoring guidance. These 15 biomarkers cover the six organ systems most affected by retatrutide.
| # | Biomarker | Why It Matters for Retatrutide | Target Range | Frequency |
|---|---|---|---|---|
| 1 | HbA1c | Retatrutide produced dose-dependent HbA1c reductions in Phase 2. Tracks long-term glycaemic response. Essential for diabetic patients; informative for non-diabetic users. | <42 mmol/mol (non-diabetic) <48 mmol/mol (diabetic target) |
Baseline, 3mo, 6mo, 12mo |
| 2 | Fasting glucose | Real-time blood sugar. Glucagon receptor activation increases hepatic glucose output, which GLP-1 and GIP components counterbalance. Monitors this equilibrium. | 3.9–5.5 mmol/L | Baseline, 3mo, 6mo, 12mo |
| 3 | ALT | Liver-specific enzyme. Retatrutide typically reduces ALT as liver fat clears, but 1% of trial participants had transient elevations >3x the upper limit. Baseline is critical. | <33 U/L (female) <41 U/L (male) |
Baseline, 3mo, 6mo, 12mo |
| 4 | AST | Found in liver, heart, and muscle. Used alongside ALT to assess liver injury pattern. The AST:ALT ratio helps distinguish between fatty liver and other causes. | <31 U/L (female) <35 U/L (male) |
Baseline, 3mo, 6mo, 12mo |
| 5 | GGT | Sensitive to bile duct obstruction and liver inflammation. Rapid weight loss increases gallstone risk. Elevated GGT can signal gallbladder complications early. | <36 U/L (female) <61 U/L (male) |
Baseline, 6mo, 12mo |
| 6 | Creatinine | Primary kidney function marker. GI side effects (nausea, vomiting, diarrhoea) cause dehydration that can temporarily impair kidney function. Rising creatinine is an early warning. | 49–90 μmol/L (female) 62–106 μmol/L (male) |
Baseline, 3mo, 6mo, 12mo + ad hoc |
| 7 | eGFR | Estimated glomerular filtration rate — calculated from creatinine, age, and sex. Gives a percentage of kidney function. Declining eGFR warrants immediate attention. | >90 mL/min/1.73m² | Baseline, 3mo, 6mo, 12mo + ad hoc |
| 8 | TSH | Thyroid-stimulating hormone. Retatrutide (like all GLP-1-class drugs) carries a precautionary C-cell tumour warning from rodent studies. TSH screens for thyroid dysfunction. Weight loss may alter levothyroxine requirements. | 0.27–4.2 mIU/L | Baseline, 6mo, 12mo |
| 9 | Total cholesterol | TRIUMPH-4 showed clinically meaningful improvements in lipids. Tracking total cholesterol, alongside non-HDL and triglycerides, quantifies cardiovascular risk reduction. | <5.0 mmol/L | Baseline, 6mo, 12mo |
| 10 | Triglycerides | Retatrutide's glucagon component increases fatty acid oxidation, which directly reduces triglycerides. One of the strongest expected improvements on this medication. | <1.7 mmol/L (fasting) | Baseline, 6mo, 12mo |
| 11 | Amylase | Pancreatic enzyme. Asymptomatic elevations were observed in retatrutide trials. Baseline establishes your normal. A sharp rise with abdominal pain could signal pancreatitis. | 28–100 U/L | Baseline, 6mo, 12mo |
| 12 | Lipase | More specific pancreatic marker than amylase. Lipase elevations were the more common pancreatic finding in retatrutide trials. One serious adverse event (acute pancreatitis) was reported in Phase 2. | <60 U/L | Baseline, 6mo, 12mo |
| 13 | Vitamin D | Already deficient in ~20% of UK adults. Reduced food intake compounds the problem. Essential for bone health, immune function, and mood — all relevant during rapid weight loss. | >75 nmol/L (optimal) 50–75 nmol/L (adequate) |
Baseline, 6mo, 12mo |
| 14 | Ferritin | Iron stores. Reduced caloric intake — especially reduced red meat — depletes ferritin within months. Fatigue from iron deficiency is easily misattributed to the medication itself. | 30–150 ng/mL (female) 30–400 ng/mL (male) |
Baseline, 6mo, 12mo |
| 15 | hsCRP | High-sensitivity C-reactive protein. TRIUMPH-4 showed meaningful hsCRP reductions with retatrutide. Tracks systemic inflammation and cardiovascular risk. A rising CRP on treatment warrants investigation. | <1.0 mg/L (low risk) 1.0–3.0 mg/L (moderate) >3.0 mg/L (high risk) |
Baseline, 6mo, 12mo |
Pre-Treatment Baseline: Why It Cannot Be Skipped
A baseline blood test before starting retatrutide serves three purposes that no subsequent test can replace:
1. Establish Your Personal Reference Values
Population reference ranges are broad. An ALT of 38 U/L is technically normal for a man — but if your personal baseline is 18 U/L, a jump to 38 at the 3-month mark represents a genuine doubling that warrants investigation. Without a baseline, this change would be invisible.
Retatrutide affects so many biomarkers simultaneously that your prescriber needs to know what "normal" looks like for you — not just for the general population.
2. Rule Out Contraindications
Based on the exclusion criteria used in retatrutide clinical trials and the known precautions for GLP-1-class medications, blood tests can identify several potential contraindications:
- Thyroid abnormalities: A personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2) is a contraindication for all GLP-1-class drugs. Baseline TSH screening is a standard precaution.
- Severe kidney impairment: Significantly reduced eGFR increases the risk that GI-related dehydration could cause acute kidney injury.
- Active liver disease: While retatrutide improves fatty liver, active hepatitis or severely elevated liver enzymes require evaluation before treatment.
- History of pancreatitis: Baseline amylase and lipase values allow your prescriber to distinguish pre-existing elevations from drug-related changes.
3. Identify Pre-Existing Conditions That May Affect Treatment
Undiagnosed type 2 diabetes, subclinical hypothyroidism, iron deficiency anaemia, or pre-existing fatty liver disease all influence how your body responds to retatrutide and how your prescriber manages your care. A comprehensive baseline panel catches these conditions before the first injection.
Get Your Pre-Treatment Baseline Blood Test
The Peak Insights 70 tests 70 biomarkers across every panel recommended for retatrutide monitoring — including HbA1c, full liver function, kidney markers, thyroid, lipids, pancreatic enzymes, vitamins, and inflammation markers. Results in 2 working days with a nurse visit to your home.
Order Peak Insights 70 →Need fewer markers? The Core Health 45 covers the most critical biomarkers at a lower price.
Retatrutide Monitoring Schedule: Baseline to 12 Months
The following schedule is based on monitoring timepoints used in the TRIUMPH trial programme and established best practice for GLP-1-class medications. Retatrutide uses a dose-escalation protocol — typically starting at 1 mg weekly and increasing to a maintenance dose of 8–12 mg over several months — so the early monitoring windows align with periods of dose increase and peak GI side effect risk.
| Biomarker | Baseline | 3 Months | 6 Months | 12 Months |
|---|---|---|---|---|
| HbA1c | ✓ | ✓ | ✓ | ✓ |
| Fasting glucose | ✓ | ✓ | ✓ | ✓ |
| ALT | ✓ | ✓ | ✓ | ✓ |
| AST | ✓ | ✓ | ✓ | ✓ |
| GGT | ✓ | — | ✓ | ✓ |
| Creatinine | ✓ | ✓ | ✓ | ✓ |
| eGFR | ✓ | ✓ | ✓ | ✓ |
| TSH | ✓ | — | ✓ | ✓ |
| Total cholesterol | ✓ | — | ✓ | ✓ |
| Triglycerides | ✓ | — | ✓ | ✓ |
| Amylase | ✓ | — | ✓ | ✓ |
| Lipase | ✓ | — | ✓ | ✓ |
| Vitamin D | ✓ | — | ✓ | ✓ |
| Ferritin | ✓ | — | ✓ | ✓ |
| hsCRP | ✓ | — | ✓ | ✓ |
Why 3-month testing is focused on metabolic, liver, and kidney markers: The first 12 weeks typically coincide with dose escalation, when GI side effects are most intense and the risk of dehydration-related kidney stress is highest. Liver enzymes are checked early to catch the rare transient ALT elevation identified in Phase 2 data. Lipid, pancreatic, nutritional, and inflammatory markers change more gradually and are assessed from 6 months onwards.
Ad hoc testing: If you experience persistent vomiting, diarrhoea, or signs of dehydration at any point during treatment, request creatinine and eGFR testing promptly. Do not wait for the next scheduled panel. Similarly, severe upper abdominal pain radiating to the back warrants immediate amylase and lipase testing to rule out pancreatitis.
What to Watch For: Red Flags on Retatrutide Blood Tests
Most blood test changes on retatrutide will be positive — improving liver enzymes, better lipid profiles, lower HbA1c, reduced inflammation. However, the following results require immediate discussion with your prescriber:
Red Flags — Contact Your Prescriber
- ALT or AST >3x upper limit of normal — Occurred in ~1% of retatrutide trial participants. Usually transient, but requires follow-up testing and clinical assessment. Stop treatment if accompanied by jaundice.
- eGFR declining by >25% from baseline — May indicate acute kidney injury from dehydration. Ensure adequate fluid intake (2–3 litres daily). May require dose reduction or temporary treatment hold.
- Lipase or amylase >3x upper limit of normal with abdominal pain — Potential pancreatitis. Seek urgent medical attention. One serious case of acute pancreatitis was reported in the Phase 2 trial.
- TSH outside normal range with symptoms — New-onset fatigue, weight changes unrelated to diet, palpitations, or heat/cold intolerance warrant thyroid investigation. Existing levothyroxine users may need dose adjustment as weight changes.
- Ferritin <15 ng/mL — Iron deficiency is certain at this level. Causes fatigue, breathlessness, and hair loss that patients commonly misattribute to retatrutide itself. Iron supplementation is straightforward once diagnosed.
- Fasting glucose <3.5 mmol/L — Hypoglycaemia risk is low with retatrutide alone, but increases if combined with insulin or sulphonylureas. Report any episodes of shakiness, sweating, or confusion.
- hsCRP rising significantly from baseline — Expected direction is improvement. A rising CRP suggests a new inflammatory process unrelated to retatrutide that warrants investigation.
How Retatrutide Monitoring Differs From Semaglutide and Tirzepatide
If you are switching from semaglutide (Wegovy/Ozempic) or tirzepatide (Mounjaro/Zepbound), your monitoring panel should expand to account for retatrutide's unique glucagon receptor activity:
- Pancreatic enzymes (amylase, lipase): Not routinely monitored on semaglutide, but should be included for retatrutide given the trial safety signal. A baseline is essential for comparison.
- More frequent liver monitoring: While semaglutide and tirzepatide both improve liver markers, retatrutide's glucagon component places additional metabolic load on the liver. The 1% rate of ALT elevations >3x ULN is higher than typically reported with semaglutide. The Phase 2a MASLD trial tracked liver-specific fibrosis biomarkers (K-18, pro-C3, FIB-4) that are not standard in routine blood panels but may become relevant as clinical experience grows.
- Beta-hydroxybutyrate (optional): Retatrutide increased this marker of fatty acid oxidation two- to threefold at doses of 4 mg and above, reflecting the glucagon-driven increase in fat burning. This is not a standard clinical biomarker, but if your blood test panel includes it, expect elevated values — this is a positive metabolic signal, not a cause for concern.
For a detailed comparison of all three medications, see our guide to retatrutide vs semaglutide.
How to Get These Tests in the UK
When retatrutide becomes available in the UK (currently expected after MHRA review, potentially 2027–2028), your prescriber will order certain blood tests as part of the prescribing protocol. However, NHS blood test panels are often limited to the biomarkers immediately required for prescribing decisions — they rarely include the full 15-marker panel recommended above.
Private blood testing fills this gap. You can order a comprehensive panel without a GP referral, have a qualified nurse visit your home or workplace for the blood draw, and receive results online within 2 working days.
Recommended Lola Health Panels for Retatrutide Users
| Test | Biomarkers | Coverage | Best For |
|---|---|---|---|
| Peak Insights 70 | 70 | All 15 essential biomarkers + additional cardiovascular, hormonal, and nutritional markers | Baseline and 6-month comprehensive panels. Ideal for complete retatrutide monitoring. |
| Core Health 45 | 45 | Covers HbA1c, liver (ALT, AST, GGT), kidney (creatinine, eGFR), thyroid (TSH), lipids, vitamins, CRP | 3-month and 12-month follow-ups. Covers the most critical markers at a lower price point. |
Both panels use venous blood collection (not finger prick), which provides laboratory-grade accuracy across all biomarkers. A qualified nurse visits your home or workplace — there is no need to travel to a clinic or hospital.
Start Monitoring With the Right Blood Test
Whether you are building a baseline before retatrutide becomes available or monitoring during treatment, the Peak Insights 70 covers every biomarker in this guide — plus 55 additional markers for a complete health picture. Results in 2 working days.
Order Peak Insights 70 →Or start with the Core Health 45 for essential monitoring.
Get All 15 Retatrutide Monitoring Biomarkers in One Test
The biomarkers that matter most on retatrutide — HbA1c, fasting glucose, ALT, AST, GGT, creatinine, eGFR, total cholesterol, LDL, HDL, triglycerides, TSH, lipase, amylase, and FBC — are all included in a comprehensive blood panel. Test before starting, then at 3-month intervals to track safety and efficacy.
All results reviewed by a doctor. Free delivery. Results in 2-3 working days.
Frequently Asked Questions
What blood tests do I need before starting retatrutide?
A comprehensive baseline should include HbA1c, fasting glucose, liver function (ALT, AST, GGT), kidney function (creatinine, eGFR), thyroid function (TSH), lipids (cholesterol, triglycerides), pancreatic enzymes (amylase, lipase), and nutritional markers (vitamin D, ferritin, hsCRP). The Peak Insights 70 blood test covers all 15 essential biomarkers in a single panel.
How often should I have blood tests on retatrutide?
Test at baseline (before starting), 3 months, 6 months, and 12 months. The 3-month test focuses on metabolic, liver, and kidney markers — the areas most affected during dose escalation. The 6- and 12-month tests are comprehensive and include all 15 biomarkers. If you experience persistent vomiting or diarrhoea, request kidney function tests immediately rather than waiting for the next scheduled panel.
Does retatrutide affect liver function?
In most participants, retatrutide improves liver function. The Phase 2a MASLD trial showed liver fat reductions of up to 86% at the 12 mg dose, with 93% of participants achieving normal liver fat levels. Mean ALT and AST levels were unchanged or had decreased at 48 weeks. However, transient ALT elevations exceeding 3x the upper limit of normal occurred in approximately 1% of participants, making baseline and follow-up testing essential.
Is retatrutide safe for the kidneys?
Retatrutide has not shown direct kidney toxicity in clinical trials. The primary kidney risk comes from dehydration caused by gastrointestinal side effects (nausea, vomiting, diarrhoea), which can temporarily reduce kidney function. Monitoring creatinine and eGFR at each testing interval — and maintaining adequate hydration of 2–3 litres daily — is the recommended approach.
What is the thyroid cancer risk with retatrutide?
Like all GLP-1-class medications, retatrutide carries a precautionary warning based on thyroid C-cell tumours observed in rodent studies. No cases of medullary thyroid cancer or C-cell hyperplasia were reported in human clinical trials. The medication is expected to be contraindicated for anyone with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). Baseline TSH testing is a standard safety measure.
Can retatrutide cause pancreatitis?
Asymptomatic elevations in amylase and lipase were observed in the Phase 2 trial, with one serious adverse event of acute pancreatitis reported. The risk appears to be low but not zero. Baseline amylase and lipase testing establishes your normal values so that any future elevations can be properly assessed. Severe upper abdominal pain radiating to the back during treatment should be evaluated urgently, regardless of blood test results.
When will retatrutide be available in the UK?
Retatrutide is currently in Phase 3 clinical trials (the TRIUMPH programme). Phase 3 results are expected to complete in mid-2026, after which Eli Lilly would submit for regulatory approval. MHRA review typically takes 12–18 months, with a NICE technology appraisal adding a further 6–12 months for NHS funding decisions. Most estimates place UK availability at 2027–2028 through private clinics, with NHS prescribing potentially from 2028–2029. You can start building your health baseline now with a comprehensive blood test so you have comparison data ready when treatment becomes available.
Do I need to fast before a retatrutide monitoring blood test?
Yes — a 10–12 hour overnight fast is recommended for accurate fasting glucose, triglyceride, and lipid measurements. You can drink water freely during the fast. If you are already taking retatrutide, inject on the same day of the week as usual (it is a once-weekly injection) — the timing relative to your blood draw does not affect results.
Medical Disclaimer
This article is for informational purposes only and does not constitute medical advice. Retatrutide (LY3437943) is an investigational medication that has not been approved by the MHRA for use in the UK. It is currently in Phase 3 clinical trials (the TRIUMPH programme, Eli Lilly). Information in this article is based on published clinical trial data and may change as further results become available. Blood test results should always be interpreted by a qualified healthcare professional in the context of your individual health history. Lola Health provides blood testing services; we do not prescribe, supply, or recommend retatrutide or any other prescription medication.
Content reviewed: February 2026. Sources include Jastreboff et al., NEJM 2023 (Phase 2 trial, NCT04881706); Sanyal et al., Nature Medicine 2024 (Phase 2a MASLD trial); Eli Lilly TRIUMPH-4 press release (December 2025); ClinicalTrials.gov registrations NCT05929066, NCT05931367, NCT06383390; MHRA GLP-1 receptor agonist safety guidance; NICE NG28 (type 2 diabetes management).
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