Peptide blood work: which labs to request

If you are using peptides (particularly growth hormone secretagogues or GLP-1 receptor agonists) and want to know which labs your clinician may want to order, the short answer is: it depends on what you are taking. But a handful of markers come up repeatedly in prescribing information, clinical guidelines, and endocrine practice. This article covers the ones that matter most and explains why each is tracked.

To be direct: this is not a protocol. It is a reference list of lab markers that appear in published prescribing information and clinical guidelines. Your clinician picks the panel; your job is to show up informed enough to have the conversation.

IGF-1 and growth hormone markers

If you are using exogenous growth hormone or a GH secretagogue (such as ipamorelin or CJC-1295), serum IGF-1 is the single most informative lab. The StatPearls physiology reference notes that conventional serum GH measurements are "almost useless" because growth hormone is released in pulses; levels swing from undetectable to very high within the same hour^[1]. IGF-1, by contrast, reflects the integrated GH signal over time and stays relatively stable from draw to draw.

The Endocrine Society's clinical practice guideline on adult GH deficiency (Molitch et al., 2011) recommends titrating GH replacement to keep IGF-1 within the age-adjusted normal range^[2]. Clinicians may also check IGFBP-3 (insulin-like growth factor binding protein 3) alongside IGF-1 for a fuller picture^[1]. Supraphysiological IGF-1 levels are clinically relevant: chronically elevated IGF-1 is associated with acromegalic features, insulin resistance, and theoretical oncological concerns.

The 2007 GH Research Society consensus guidelines also specify that clinicians should monitor "biochemistry, body composition, and quality of life" as part of ongoing assessment during GH therapy[3].

Fasting glucose and HbA1c

Growth hormone is a counter-regulatory hormone: it opposes insulin's action and raises blood glucose. The literature reports that exogenous GH can reduce insulin sensitivity, which is why fasting glucose and HbA1c monitoring appear in clinical GH treatment guidelines^[2]. This applies to pharmaceutical somatropin, but the same metabolic logic extends to any compound that meaningfully raises GH or IGF-1.

For GLP-1 receptor agonists like semaglutide or tirzepatide, glucose monitoring runs in the other direction. These drugs lower blood glucose. The Ozempic prescribing information notes that dose escalation is guided by glycaemic response^[4]. HbA1c is the standard long-term glucose marker for anyone on an incretin-class drug, and fasting glucose gives the acute picture.

Lipid panel

A standard lipid panel (total cholesterol, LDL, HDL, triglycerides) is relevant for most peptide users, but especially for those on GH or GLP-1 class drugs. GH affects lipolysis and lipid metabolism; GLP-1 agonists have shown favourable effects on cardiovascular markers in large trials. Your clinician will want a baseline and periodic follow-ups to track how the lipid profile is responding.

Liver and kidney function

A standard metabolic panel (CMP) covers both. Liver enzymes (ALT, AST, ALP) and kidney markers (creatinine, BUN, eGFR) give your clinician a read on organ stress. The Mounjaro prescribing information flags renal function monitoring specifically when initiating or escalating doses in patients with renal impairment who experience severe gastrointestinal reactions^[5]. The Ozempic label carries a similar note: "monitor renal function in patients reporting adverse reactions that could lead to volume depletion"^[4].

Liver function tests matter for a different reason. Many compounds are hepatically metabolised, and any injectable regimen that bypasses first-pass metabolism still loads the liver indirectly. A baseline CMP before starting any peptide course, followed by periodic rechecks, is standard clinical practice.

Thyroid markers

Both the Ozempic and Mounjaro labels carry a boxed warning about thyroid C-cell tumours observed in rodents^[4][5]. The labels note that routine serum calcitonin monitoring or thyroid ultrasound "is of uncertain value" for detecting medullary thyroid carcinoma in humans. Still, a baseline TSH and free T4 give the clinician a reference point. Bezin et al. (2023) reported in Diabetes Care that GLP-1 receptor agonist use for 1 to 3 years was associated with an increased hazard ratio for thyroid cancer (HR 1.58, 95% CI 1.27 to 1.95)^[6]. That signal is still being characterised, but it underscores why thyroid function at baseline matters.

Complete blood count

A CBC (complete blood count) is not peptide-specific, but it rounds out the safety baseline. It covers red blood cells, white blood cells, haemoglobin, haematocrit, and platelet count. If you are using multiple compounds, a CBC gives your clinician a read on haematological health that single-marker panels miss.

Pancreatic markers

The Ozempic prescribing information reports that clinical trials showed mean increases from baseline in amylase (13%) and lipase (22%)^[4]. Acute pancreatitis is a recognised adverse event for the GLP-1 class. If you are on a GLP-1 agonist, your clinician may check lipase and amylase at baseline and if you report persistent severe abdominal pain.

When to draw labs

Most clinicians will want a full baseline panel before you start any peptide course. For ongoing monitoring, the interval depends on what you are taking and your individual risk factors. A common pattern is baseline, 6 to 8 weeks in, and then every 3 to 6 months for stable regimens. Your clinician will set the schedule based on your situation.

What we do not yet know

The monitoring recommendations above are drawn from prescribing information for approved pharmaceuticals (somatropin, semaglutide, tirzepatide) and clinical guidelines for GH therapy. For grey-market peptides (BPC-157, semax, TB-500, and similar), there are no published monitoring guidelines at all. We do not have clinical trial data defining which labs to track, at what intervals, or what thresholds signal a problem. If you are using compounds that lack prescribing information, the argument for thorough lab monitoring (CMP, CBC, IGF-1, lipids, thyroid panel) is stronger, not weaker, precisely because the safety data does not exist.

This article is for education. It does not replace a conversation with your clinician, and it does not constitute medical advice. If you are considering any peptide, bring this list to a qualified healthcare provider and let them decide which markers apply to your situation.