More than 30 million Americans are now on Ozempic, Wegovy, Mounjaro, or Zepbound. Most receive no systematic blood testing protocol beyond what their prescribing physician orders at initiation. GLP-1 medications affect liver, kidneys, pancreas, thyroid, and cardiovascular markers simultaneously — and most of the meaningful changes are asymptomatic until they become serious. This is the monitoring guide that should come with the prescription.
✦
CreusLife Editorial Team
Evidence reviewed · Clinical sources cited · May 2026
⚕️Medical disclaimer: GLP-1 medications are prescription drugs. This page provides informational context for people already prescribed a GLP-1 by their physician — it does not constitute medical advice and is not a substitute for clinical monitoring by your prescribing provider. Some links are affiliate links. Full disclaimer.
📋Scope of this guide: This page covers monitoring for people already prescribed a GLP-1 by their physician. It does not cover how to obtain a GLP-1 prescription, whether GLP-1s are appropriate for your situation, or how to dose them. Those are clinical decisions between you and your prescriber. What this covers: which biomarkers to track, why each one matters, what values to watch for, and how to order testing directly.
Share
🎯Bottom line: Test these four marker groups every 90 days on a GLP-1: liver enzymes (ALT, AST, GGT), kidney function (creatinine, eGFR), metabolic response (HbA1c, fasting insulin, ApoB), and TSH. Add lipase if you have any abdominal symptoms. Add nutrient markers (vitamin D, B12, ferritin) at 6 months if you are eating substantially less. Order directly via Quest Health — no additional physician referral needed for follow-up testing.
Most baseline issues that contraindicate or complicate GLP-1 use — pre-existing liver disease, reduced kidney function, thyroid abnormalities — are asymptomatic. A comprehensive baseline lets your prescriber dose appropriately and gives you the reference points that make all future monitoring meaningful. Without a baseline, you cannot tell whether a rising creatinine is new or pre-existing.
🩸
Baseline panel — order before first dose
The complete pre-GLP-1 reference point
~$150–200 via Quest
🫀
HbA1c + Fasting Insulin
Your metabolic baseline before the medication intervenes. HbA1c shows your 90-day average glucose; fasting insulin shows how hard your pancreas has been working. Together they establish whether you are starting from insulin resistance (high insulin, elevated HbA1c) or from a cleaner metabolic state — which affects how aggressively the GLP-1 will need to work and how dramatic the 90-day response should look.
GLP-1s typically improve the lipid profile — lower triglycerides, lower ApoB, improved HDL — but individual responses vary. You need a baseline to confirm this is actually happening at your 90-day retest. ApoB specifically is more sensitive than LDL-C for detecting residual cardiovascular risk, particularly in people with metabolic syndrome who are the primary GLP-1 user population.
Systemic inflammation marker. GLP-1s have documented anti-inflammatory effects — weight loss reduces visceral fat, which is the primary source of pro-inflammatory cytokines. hs-CRP at baseline and at 90 days shows whether the anti-inflammatory effect is occurring. People with very high hs-CRP (>3 mg/L) at baseline have the most to gain from this effect.
GLP-1s are processed by the liver and GLP-1 receptors are expressed in hepatic tissue. In people with metabolic dysfunction-associated steatotic liver disease (MASLD/NAFLD), semaglutide has demonstrated ALT reduction averaging around 10 U/L — a beneficial effect. But pre-existing elevated enzymes need a baseline to distinguish drug effect from pre-existing disease. GGT is the most sensitive early marker of liver stress.
Target
ALT <25 U/L · AST <25 U/L · GGT <30 U/L
Before starting
Flag if ALT >40 or GGT >50 — discuss with physician
🫘
Kidney Function — Creatinine + eGFR
GLP-1 medications reduce appetite and thirst signals, which can lead to dehydration — particularly during the dose titration phase when nausea is most pronounced. Dehydration is the primary kidney risk mechanism. A baseline eGFR and creatinine establishes your starting kidney function so any change during treatment is detectable. People with baseline eGFR <45 need more frequent monitoring.
Flag if eGFR <60 — discuss frequency with physician
🦋
TSH (Thyroid Stimulating Hormone)
The FDA requires a black box warning on GLP-1 medications about thyroid C-cell tumors based on rodent studies — the clinical relevance in humans is uncertain but the warning reflects a real regulatory concern. More practically, GLP-1s interact with thyroid metabolism in ways not fully characterized. TSH baseline and monitoring is standard of care for GLP-1 users.
Target
0.4–4.0 mIU/L (standard) · <2.5 mIU/L (optimal)
Before starting
Flag if <0.4 or >4.0 — discuss with physician
☀️
Vitamin D (25-OH)
Not directly affected by GLP-1s — but many GLP-1 users are starting from a position of suboptimal vitamin D, and the dramatic appetite reduction that follows means total nutrient intake drops. Establishing a baseline confirms whether you are already deficient before the appetite suppression compounds the problem.
No doctor referral required. Results in 3–5 days. HSA/FSA eligible.
Every 90 days — ongoing safety and response monitoring
The 90-day interval is not arbitrary — it matches the HbA1c measurement window (90-day average glucose) and gives enough time for organ stress to appear at detectable levels before symptoms develop. Most meaningful changes on GLP-1s — lipase elevation, creatinine rise, liver enzyme shifts — are silent. You will not feel them until they are significant. Testing catches them early.
🔁
90-day panel — the core monitoring loop
Order the same panel every 90 days. Compare to your baseline and prior results — trend matters more than any single reading.
~$80–120 via Quest
🫁
ALT + AST + GGT (liver)
The most important safety markers to track on an ongoing basis. GLP-1s generally improve liver enzymes in people with fatty liver disease — a falling ALT over 90 days is a positive signal that hepatic fat is resolving. A rising ALT warrants attention. GGT is the most sensitive marker of ongoing liver stress and often rises before ALT does.
Target
ALT trending down or stable · GGT <30 U/L
Every 90 days
Rising ALT by >20 U/L: discuss with physician
🫘
Creatinine + eGFR (kidney)
The primary kidney risk on GLP-1s is dehydration-mediated, peaking during the titration phase. An eGFR declining by >10 points over 90 days warrants clinical attention. In people who are actively losing significant weight, some creatinine reduction is expected as muscle mass declines — this can actually mask true kidney function changes. Track both creatinine and eGFR together.
Target
eGFR stable or improving · Creatinine not rising
Every 90 days
eGFR dropping >10 points: discuss with physician
🫀
HbA1c + Fasting Insulin
The primary efficacy signals. HbA1c should be declining at 90 days if metabolic response is occurring. Fasting insulin often drops before HbA1c does — it is the earlier-moving marker. Someone with insulin resistance who shows declining fasting insulin at 90 days but stable HbA1c is still responding — the insulin reduction is a leading indicator that glucose improvement will follow.
Weight loss on GLP-1s typically drives a meaningful improvement in triglycerides within the first 90 days — one of the fastest-moving markers. ApoB improvement lags slightly behind triglycerides. If ApoB is not declining after 6 months of weight loss, additional dietary intervention (reduced refined carbohydrates, increased omega-3) is likely needed alongside the medication.
ApoB not declining after 6 months: add dietary intervention
🦋
TSH
Thyroid monitoring is standard on GLP-1s given the FDA black box warning. In most people, TSH remains stable throughout GLP-1 treatment. Symptoms of thyroid dysfunction — fatigue, weight changes, heart rate changes — overlap substantially with GLP-1 side effects, making objective TSH testing important for distinguishing drug effects from thyroid changes.
Target
0.4–4.0 mIU/L · Stable from baseline
Every 90 days
TSH <0.4 or >4.0: evaluate thyroid more fully
🔥
hs-CRP
One of the most reliable indicators that GLP-1 therapy is producing the expected metabolic benefit. Significant weight loss — 10%+ of body weight — consistently reduces hs-CRP as visceral fat (the primary cytokine source) decreases. A falling hs-CRP at 90 days is a positive signal. Persistently elevated hs-CRP despite weight loss may indicate other inflammatory drivers (sleep apnea, gum disease, diet quality) that need addressing.
Persistently >3.0 mg/L despite weight loss: investigate other drivers
🔬
Lipase
GLP-1 medications stimulate the pancreas, and pancreatitis — though uncommon — is a documented adverse effect. Lipase elevation above 3x the upper limit of normal, especially with abdominal symptoms, is the clinical signal. Routine lipase monitoring is not universally required by all guidelines, but is recommended by many GLP-1 prescribers given the pancreatic stimulation mechanism. If you experience abdominal pain on a GLP-1, lipase testing is urgent.
GLP-1 medications do not directly deplete nutrients — but dramatic appetite suppression means many users are eating 30–50% less than before. Over 6 months, this can produce borderline deficiencies in nutrients that are already marginal in the general population.
🧬
6-month additions — nutrient status check
Add these to your standard 90-day panel at the 6-month mark
~$40–60 additional
☀️
Vitamin D (25-OH)
Not directly depleted by GLP-1s, but reduced food intake over 6 months can lower dietary vitamin D intake, compounding any pre-existing insufficiency. Particularly relevant if you started below optimal at baseline.
Women on GLP-1s are particularly at risk for declining ferritin — dietary iron comes primarily from red meat and fortified foods, both of which may be consumed less with reduced appetite. Ferritin below 30 ng/mL causes fatigue, hair shedding, and reduced cognitive performance even before anemia develops. Check at 6 months if you have reduced meat intake or experience hair loss.
Target
>50 ng/mL optimal · >30 ng/mL minimum
6 months
Below 30 ng/mL: discuss iron supplementation with physician
💊
Vitamin B12
GLP-1 medications themselves do not deplete B12 (unlike metformin, which does). But reduced animal protein intake from appetite suppression can lower dietary B12 over time. B12 deficiency causes fatigue, neurological symptoms, and anemia — symptoms that overlap with other GLP-1 effects, making testing important for differential diagnosis.
Target
>400 pg/mL optimal
6 months
Below 300 pg/mL: supplement; below 200 pg/mL: discuss with physician
💊
Magnesium (RBC magnesium preferred)
Not a specific GLP-1 concern, but ~50% of adults are already below optimal magnesium status. Reduced food intake compounds this. Suboptimal magnesium suppresses HRV, sleep quality, and insulin sensitivity — all outcomes you are trying to optimize alongside GLP-1 therapy. Standard serum magnesium is a poor indicator of true status; request RBC magnesium if available.
At annual intervals, run the full baseline panel again. This captures the complete picture of what 12 months of GLP-1 therapy has done to your metabolic, cardiovascular, hepatic, renal, and hormonal markers. This is also when to add body composition data — DEXA scan at 12 months is the most informative single measurement for understanding whether you have lost fat or a concerning amount of lean mass alongside it.
💡
The easiest way to run a comprehensive annual panel: Function Health's annual membership (~$499) includes all of the above — liver, kidney, thyroid, metabolic, cardiovascular, hormonal, and nutrient markers — in a single annual draw. It is the highest-value comprehensive option at this price point. Quest Health allows you to order individual panels at lower total cost if you only need specific markers. Compare all platforms →
What about body composition — should I get a DEXA scan?
Yes, if you can access one affordably. The scale does not tell you what you are losing. Trial data from STEP 1 (semaglutide) and SURMOUNT-1 (tirzepatide) shows that approximately 25–40% of total weight lost on GLP-1s comes from lean mass, not just fat. For most people this is within expected ranges for any caloric restriction — but for people over 50, or those starting with lower muscle mass, it represents a meaningful risk. A DEXA scan at baseline and at 6 months tells you specifically whether you are losing fat or muscle.
Quest Health — direct ordering, no physician referral
Order the specific tests you need online. Visit any of 2,000+ Quest Patient Service Centers for a blood draw. Results in 3–5 days delivered directly to you. HSA/FSA eligible. You can show results to your prescriber or keep them for your own records. Order via Quest Health →
2
Function Health — comprehensive annual panel
160+ biomarkers including all of the above in a single annual draw. Best value if you want the complete picture rather than targeted panels. Uses Quest labs nationwide. Function Health →Compare all platforms →
3
Your prescribing physician
Most GLP-1 prescribers will order the standard safety monitoring panel (liver, kidney, TSH) at initiation. You may need to specifically request fasting insulin, ApoB, hs-CRP, and nutrient markers — these are not universally included in standard GLP-1 monitoring protocols. Bring this page to your appointment as a reference.
Clinical monitoring guidance
1
Meto.co — 10 Biomarkers Every GLP-1 Patient Should Track. April 2026. Aligns with ADA and Obesity Medicine Association guidance for pre-therapy baseline and ongoing monitoring.
Choose Health — GLP-1 Blood Tests: What to Monitor on Ozempic, Wegovy & Mounjaro. May 2026. Comprehensive clinical monitoring framework covering liver, kidney, thyroid, and metabolic markers.
Armstrong MJ et al. Liraglutide safety and efficacy in patients with non-alcoholic steatohepatitis (LEAN). Lancet. 2016. PMID: 26608256. GLP-1 effect on liver enzymes in NAFLD/MASLD.
Blood markers are one layer. Body composition — lean mass specifically — requires DEXA and functional testing. See the dedicated muscle monitoring guide.