What to test before starting any peptide — the labwork that matters

The question this piece answers is: what does a genuinely comprehensive pre-peptide baseline look like, what does each component tell you, and why does having it protect you in ways that matter both immediately and over time?

Start with the comprehensive metabolic panel. This is kidney function — creatinine, BUN, GFR — and liver function — AST, ALT, alkaline phosphatase, bilirubin — along with electrolytes, protein, and glucose. Before you introduce any compound that the body needs to metabolize and clear, you want to know your baseline renal and hepatic function. Not because most peptides are dramatically hepatotoxic, but because any future shift in those markers means something specific when you have a pre-protocol number to compare it to. Without a baseline, a modest elevation in liver enzymes at week twelve is uninterpretable. With a baseline, it's either reassuringly stable or something worth investigating.

The complete blood count gives you the hematologic and immune picture: red blood cell count, hemoglobin, hematocrit, white blood cell count with differential, platelets. This is particularly relevant for protocols that may affect hematopoiesis or immune function over time. It's also your basic safety screen — some findings that show up incidentally on a CBC warrant clinical attention before you add anything new to your system.

Fasting glucose and HbA1c are not optional context before GH-related work. They are the baseline that makes everything on the GH axis interpretable. Growth hormone secretagogues can influence insulin sensitivity, and the GLP-1 adjacent compounds being researched have metabolic implications by mechanism. If your fasting glucose is already 105 and your HbA1c is sitting at 5.8, you are close enough to prediabetic range that your clinician needs to factor this into protocol selection and monitoring frequency. If you don't test before starting, you can't distinguish a pre-existing trend from a compound-induced shift at follow-up.

The lipid panel — total cholesterol, LDL, HDL, triglycerides, and ideally ApoB — is similarly foundational. Lipid profiles shift with hormonal changes, metabolic changes, and some peptide protocols. Having your baseline makes follow-up data meaningful. A triglyceride elevation at three months means something different if your baseline was 85 versus if it was 160 before you started.

The thyroid panel deserves more attention than it typically gets in peptide intake workups, which often order TSH alone. TSH is a useful screening marker, but it misses a clinically significant number of people with thyroid dysfunction. Free T3 and free T4 give you actual tissue-available thyroid hormone levels. Reverse T3 is relevant if you suspect high-stress or high-caloric-restriction patterns that may be driving conversion problems. Thyroid antibodies — TPO and thyroglobulin — are worth including if there's any personal or family history of thyroid disease, or if symptoms suggest it. The reason this matters in the context of peptide protocols is that hypothyroidism and subclinical thyroid dysfunction produce symptoms — fatigue, poor recovery, cognitive fog, difficulty with body composition, sleep disruption — that overlap almost perfectly with the symptoms many people are pursuing peptides to address. Starting a peptide protocol without ruling out or accounting for thyroid dysfunction is starting with one of the most significant confounders unaddressed.

Sex hormones are relevant for most peptide protocols in ways that go beyond the GH axis. Total testosterone and free testosterone, SHBG, and estradiol give you the hormonal context in which the protocol will operate. Low testosterone changes the body composition response to training and nutritional interventions. SHBG affects how much of your total testosterone is bioavailable. Estradiol influences recovery, cognitive function, and mood in ways that matter across sexes. For women, FSH and LH add context around cycle phase and ovarian reserve. This isn't a tangent — it's part of the clinical picture that determines which compounds are most relevant and what effects are plausibly attributable to what.

DHEA-S and morning cortisol round out the adrenal and stress-axis picture. DHEA-S declines with age and with chronic stress. Cortisol timing matters — morning cortisol is the conventional baseline marker for HPA axis function, and a notably low or notably high result changes the clinical interpretation of fatigue, sleep disruption, and immune symptoms. If your clinician suspects cortisol dysregulation, a four-point diurnal cortisol assessment gives considerably more information than a single morning draw, though it requires either a blood draw at multiple time points or a salivary protocol.

IGF-1 is the specific baseline for GH-axis work. It reflects integrated GH secretion over time — more stable than a point-in-time GH measurement — and tells you both where your baseline axis activity sits and what the protocol is doing to it over time. If you're considering Sermorelin, Ipamorelin, CJC-1295, or similar compounds, your pre-protocol IGF-1 is the number your clinician needs.

The foundational micronutrient panel is where a lot of clinicians cut corners, partly because patients don't ask for it and partly because it feels tangential. It isn't. 25-OH vitamin D, ferritin, B12, folate, and serum or RBC magnesium are the basic nutritional picture, and deficiencies in any of these can produce fatigue, cognitive symptoms, recovery problems, mood disruption, and immune dysregulation — the same symptom clusters that lead people toward peptide protocols in the first place. Starting a protocol without knowing your vitamin D is 19 ng/mL, your ferritin is 14, or your B12 is borderline low means you may spend months and meaningful money on a peptide protocol when a $20 supplement and dietary change would have addressed a significant portion of what you're experiencing. This is not a reason not to pursue the peptide protocol; it's a reason to have the complete picture first.

Inflammatory markers — at minimum hsCRP, and sometimes ESR or a broader panel — tell you where your systemic inflammation baseline sits. Elevated hsCRP has implications for cardiovascular risk, for metabolic health, and for the recovery and tissue-repair endpoints that some peptides are researched for. A CRP of 0.4 at baseline and 0.4 at follow-up is informative. A CRP of 0.4 at baseline and 2.1 at follow-up is a signal.

For women, menstrual cycle tracking — either symptom-based or with mid-luteal progesterone and cycle-day-appropriate estradiol — adds relevant context before protocols that may interact with the hormonal axis. Some clinicians also recommend a sleep study or at minimum a validated sleep questionnaire before peptide protocols focused on sleep or GH stimulation, because undiagnosed sleep apnea changes both the interpretation of symptoms and the safety calculus.

The honest cost picture: a comprehensive panel like this, run through a standard lab, typically costs $200 to $500 depending on what's included and how it's ordered. At a direct-to-consumer lab service, you can get close to this picture for less. Some of it may be covered depending on your insurance and how your clinician codes the visit. The cost-versus-value calculation is worth doing explicitly: the information this panel provides protects your interpretation of everything that follows, catches findings that should be addressed before you add new variables, and gives your clinician the clinical context to actually guide your protocol rather than make educated guesses. Starting without it is a false economy.

The comprehensive baseline also does something that's harder to quantify: it establishes a relationship with your clinician built on real data rather than reported symptoms alone. Your clinician who has reviewed your full panel before starting is better positioned to evaluate your follow-up data, interpret unexpected changes, and make informed decisions about what to continue, adjust, or stop. The labs are not bureaucratic overhead. They are the foundation of the clinical relationship that makes the rest of this work.