Lab Literacy / The Baseline Bloodwork Researchers Start With
8 min readA peptide trial does not begin with a peptide. It begins with a blood draw.
Before a participant receives a single dose in any published study, researchers run a baseline panel — a specific set of blood tests and body measurements that serves three purposes: confirm the person actually fits the study, establish a reference point every future result is measured against, and flag anything that could make the intervention dangerous.
That panel isn't arbitrary. Every test in it earned its place through one of the major trials — tesamorelin's HIV-lipodystrophy studies, the SURMOUNT and SUSTAIN programs for tirzepatide and semaglutide, or Endocrine Society guidelines for growth hormone replacement. If you read enough of these trials, the same tests appear over and over, because the same physiological systems keep mattering.
Here is the standard baseline panel, organized by what it monitors. Every number traces to a published trial enrollment criterion or a clinical guideline — not a community consensus, not a vendor recommendation sheet.
These are the tests that tell researchers where a participant's metabolism and hormone systems stand before anything is changed.
| Marker | What it measures | Why peptide research cares |
|---|---|---|
| Fasting glucose | Morning blood sugar (fasting 8-12 h) | Baseline for GLP-1 trial eligibility; GH raises glucose, so researchers track this throughout |
| Fasting insulin | Pancreatic insulin output | Needed to calculate HOMA-IR; SURMOUNT trials tracked it at multiple timepoints |
| HbA1c | 90-day average blood glucose | SUSTAIN trials required HbA1c of at least 7% to enroll; SURMOUNT used it to exclude undiagnosed diabetes |
| HOMA-IR | (fasting glucose x fasting insulin) / 405 | Insulin resistance surrogate; SURMOUNT-1 tracked HOMA2-IR reduction as an endpoint. Research threshold is generally 2.0-2.5 |
| Lipid panel | Total cholesterol, LDL-C, HDL-C, triglycerides | Tesamorelin trials measured triglyceride reduction as a secondary endpoint; GH affects lipid metabolism broadly |
| ApoB | Atherogenic particle count | Better than LDL-C for cardiovascular risk assessment; optimal is below 80 mg/dL |
| Lp(a) | Genetically determined CVD risk | Above 50 mg/dL is high risk per ACC guidelines; stable over a lifetime, so it serves as a fixed baseline context |
| TSH / fT3 / fT4 | Thyroid axis function | SURMOUNT excluded anyone with TSH outside 0.4-6.0 mIU/L; GH affects the conversion of T4 to T3 |
| Cortisol (AM) | HPA axis function | Drawn between 7-9 AM; normal range 6.2-25 mcg/dL. Baseline before any GH-axis intervention |
| IGF-1 | Integrated GH secretion | The primary biomarker for the entire GH-axis peptide class (tesamorelin, CJC-1295, ipamorelin, MK-677) |
| Testosterone, estradiol, DHEA-S, prolactin | Sex and adrenal hormones | Body-composition confounders; some GH secretagogues may elevate prolactin |
A few things stand out when you see the panel laid out this way. The thyroid tests are there not because peptides directly affect the thyroid, but because growth hormone changes how the body converts T4 into its active form, T3. If a participant starts with borderline thyroid function, that conversion shift can push them into a clinically meaningful range. The SURMOUNT trials drew that line explicitly: TSH below 0.4 or above 6.0, and you're out.
HbA1c serves a different kind of gate. It is not a safety test — it is an eligibility fence. The SUSTAIN semaglutide trials enrolled only people with HbA1c between 7% and 10%, which meant they already had type 2 diabetes. The SURMOUNT tirzepatide trials did the reverse: they excluded undiagnosed diabetes, which is why they required HbA1c below 6.5% in the non-diabetic arm. Same test, opposite sides of a line that separates two entirely different trial populations.
No trial gives an intervention without first confirming the organs that will process it can handle it. This is the safety gatekeeping panel, and it is remarkably consistent across peptide classes.
| Marker | What researchers check | The trial line |
|---|---|---|
| CBC (complete blood count) | Standard safety monitoring | Required in every major trial |
| CMP (comprehensive metabolic panel) | Liver enzymes (ALT ~4-56, AST ~8-40, GGT 5-40 U/L) | SURMOUNT excluded ALT above 3x the upper limit of normal |
| eGFR / creatinine / BUN | Kidney function | SURMOUNT excluded eGFR below 30; normal BUN:creatinine ratio is 10-20:1 |
| Lipase / amylase | Pancreatic enzymes | Pancreatitis surveillance specific to the GLP-1 drug class |
| hs-CRP | Systemic inflammation | AHA/CDC tiers: below 1.0 low, 1.0-3.0 moderate, above 3.0 mg/L high cardiovascular risk; above 10 means retest (acute confound) |
| Homocysteine | Vascular risk | Above 15 micromol/L is an independent cardiovascular risk factor |
The calcitonin test deserves a special mention because its inclusion is specific and deliberate. SURMOUNT trials measured calcitonin at baseline and excluded participants whose levels were too high — 20 ng/L or above if kidney function was normal, 35 ng/L or above if it was reduced. The reason: calcitonin is a tumor marker for medullary thyroid carcinoma, and GLP-1 receptor agonists carry a theoretical concern about accelerating that specific cancer type. It is a narrow, specific gate for a narrow, specific risk — and it only appears in GLP-1 trials because the concern is class-specific.
Blood tests do not capture everything researchers need. The baseline also includes physical measurements, and in some trials these are more important than any lab value.
| Measure | Research role |
|---|---|
| Visceral adipose tissue (CT scan at L4-L5) | The FDA's primary endpoint for tesamorelin — roughly 15% VAT reduction at 26 weeks, roughly 18% at 52 weeks. The only peptide approved on an imaging endpoint. |
| DEXA scan | SURMOUNT-1 substudy body-composition endpoint; MK-677 trials used it for fat-free mass |
| Waist circumference | Tesamorelin required 95 cm or more (men) or 94 cm or more (women) just to enroll; SURMOUNT tracked it as an efficacy measure |
| BMI | SURMOUNT required 30 or above, or 27 plus a weight-related comorbidity |
Tesamorelin is the standout here. It is the only peptide in this space with an FDA approval based on an imaging endpoint — a CT scan measuring visceral adipose tissue at the L4-L5 vertebral level, not a scale weight or a blood marker. The enrollment bar was structural: you had to demonstrate abnormal visceral fat distribution before you could receive the drug. That is a different kind of baseline than a blood draw. It is a photograph.
The panels above cover the full scope, but not every trial runs every test. The selections narrow by what each peptide class actually affects.
GLP-1 agonists (semaglutide, tirzepatide) focus on: fasting glucose, HbA1c, fasting insulin, lipase and amylase for pancreatitis surveillance, CMP, calcitonin, lipids, and TSH. The pancreatitis watch is class-specific — it exists because GLP-1 agonists slow gastric emptying, and pancreatic inflammation is a known adverse effect.
GH-axis peptides (tesamorelin, CJC-1295, ipamorelin, MK-677) focus on: IGF-1 as the primary biomarker, fasting glucose, HbA1c, morning cortisol, full thyroid panel, prolactin, lipids, and CMP. The IGF-1 test is non-negotiable here — it is the direct readout of whether the intervention is doing what it is supposed to do.
Regenerative peptides (BPC-157, TB-500) are a different category entirely. No FDA-standardized human trial panels exist for these compounds. Any lab protocol for them derives from clinician experience and extrapolation, not from the kind of large-scale trial data that shaped the panels above. The responsible research baseline is the organ-safety subset: CBC, CMP, and inflammatory markers like hs-CRP and IL-6.
When you see a peptide study that reports results, the baseline panel is what makes those results interpretable. A 15% reduction in visceral fat means something precise because the trial measured VAT with a CT scan at baseline and again at 26 weeks. An IGF-1 increase from 141 to 219 mcg/L means something because the starting point was established first.
The absence of a baseline is as informative as its presence. If a study or a protocol does not report what was measured before the intervention began, the results that follow are unmoored. You cannot evaluate change without knowing what changed from.
The other pattern worth noticing: trials use these same tests as both enrollment gates and monitoring endpoints. HbA1c determines whether you get into a GLP-1 trial, and then it is tracked every 12 weeks to measure whether the drug is working. IGF-1 determines the starting dose in GH-replacement guidelines, and then it is checked every 4 to 8 weeks during titration. The baseline is not a one-time formality. It is the reference that every subsequent measurement is judged against.
This article is for educational purposes and is not medical advice. It describes what published clinical trials measure and why. It does not recommend any test, peptide, or protocol. Decisions about testing or treatment belong with a qualified clinician who knows your medical history.
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