Lab Checklist Before Peptide Therapy

One of the most common questions people bring to a first hormone or peptide therapy consultation is some version of: “I think something is off, but my doctor said my labs are normal.” It is a frustrating place to be. Symptoms are real, they affect quality of life, and yet the results come back without a flag in sight.

Part of what drives that experience is a mismatch between standard care lab panels and the more complete picture that hormone optimization actually requires. A standard annual blood panel might check glucose, a lipid panel, a complete blood count, and perhaps a TSH. It rarely includes IGF-1. It may not include free testosterone. It almost certainly does not include SHBG or a measure of estradiol in a perimenopausal woman. And without those numbers, a provider cannot determine whether the GH axis, the testosterone axis, or another hormonal pathway is contributing to what the patient is feeling.

This guide covers which laboratory tests matter before starting any peptide or hormone therapy protocol, why each one is clinically relevant, how to think about timing and preparation, and what the ongoing monitoring picture looks like once therapy begins. Understanding this before your first consultation puts you in a much stronger position to have a productive conversation.

Why Baseline Labs Are Not Optional

Baseline testing before peptide or hormone therapy serves several distinct purposes that go beyond simply satisfying a checkbox. The first is confirming that a given biological axis is actually suboptimal. Symptoms of low testosterone, GH decline, or thyroid dysfunction overlap substantially, and treating the wrong axis does nothing for the patient. A below-range IGF-1 supports a clinical rationale for GH secretagogue consideration. A normal IGF-1 means that pathway is not the relevant gap, regardless of how the patient feels.

The second purpose is establishing a reference point. Without pre-treatment values, it is genuinely impossible to determine whether therapy is working or causing unintended changes. This is not a theoretical concern. Studies document that 25 to 38% of patients on TRT require dose adjustments based on ongoing monitoring, and that finding depends entirely on having a baseline to compare against.

The third purpose is identifying contraindications. Pre-existing conditions such as elevated PSA, a hematocrit above threshold, impaired liver or kidney function, or an active malignancy change the entire risk calculation. Some of these findings mean a protocol needs modification. Others mean it should not begin at all until a separate issue is addressed. None of this is visible without labs.

The Hormone Panel

The foundation of any pre-therapy evaluation is a comprehensive hormone panel. The specific tests included will vary based on sex, age, and what protocols are being considered, but several markers belong in virtually every evaluation.

IGF-1

If someone is considering a GH-stimulating peptide like Sermorelin or Tesamorelin, IGF-1 is the single most important baseline test. Because growth hormone is released in pulses throughout the day and night, measuring GH directly at a single blood draw is not clinically useful. IGF-1, produced by the liver in response to GH over time, provides a stable and reliable picture of average GH axis activity. A below-range IGF-1 supports the clinical rationale for GH secretagogue consideration. A normal or elevated result means the GH axis is not the relevant gap. IGF-1 also becomes the primary monitoring marker once therapy begins, measured at 3 and 6 months to assess response.

Total and Free Testosterone

Total testosterone measures all testosterone in circulation, including the portion bound to carrier proteins. Free testosterone is the biologically active fraction, typically only 2 to 3% of total, that is available to enter cells and produce effects. A patient can have a normal total testosterone but meaningfully low free testosterone if the binding protein SHBG is elevated, which is common in older adults and is frequently the reason for symptoms that seem inconsistent with a “normal” result.

Morning testing, between 7 and 10 AM, is required for testosterone measurements. Testosterone follows a pronounced diurnal rhythm and can read 20 to 30% lower in the afternoon than the same individual would show in the morning. An afternoon draw that comes back borderline is not a reliable result. For more on what testosterone values mean in the context of symptoms, the article Signs of Low Testosterone in Men Over 40 covers the clinical picture in detail.

SHBG

Sex hormone-binding globulin is the protein that binds to testosterone and estradiol, making them unavailable for tissue use. SHBG is needed to calculate free testosterone accurately and is often the explanation for low free testosterone despite normal total testosterone. Elevated SHBG is common in older adults, in people who take oral estrogen or certain medications, and in those with thyroid dysfunction. Without this value, free testosterone cannot be correctly interpreted.

Estradiol

Estradiol (E2) is relevant for both men and women in any hormone protocol evaluation. In men, testosterone converts naturally to estradiol through aromatization, and the balance between the two matters for mood, libido, bone density, and cardiovascular health. In women, estradiol is the primary estrogen and the central hormone of the menopause conversation. Baseline estradiol is required before any testosterone or hormone replacement protocol to inform estrogen management decisions and to establish where the patient sits in the hormonal transition. The companion article Menopause and Hormones: What Women Over 45 Need to Know covers the women’s perspective on this in depth.

LH and FSH

Luteinizing hormone and follicle-stimulating hormone are pituitary hormones that signal the gonads to produce testosterone and estrogen respectively. Their values reveal whether a testosterone deficiency is primary (the testes or ovaries are not responding) or secondary (the signal from the pituitary is insufficient). This distinction matters clinically because the cause of the deficiency affects the treatment approach. In women, FSH is also used to stage the menopause transition. A significantly elevated FSH in a woman with irregular cycles is a strong indicator of the perimenopausal state.

Thyroid Panel

Thyroid dysfunction is among the most common mimics of hormonal decline. Hypothyroidism produces fatigue, weight gain, cognitive slowing, mood changes, and reduced recovery capacity that look nearly identical to the symptoms of low testosterone or GH axis decline. The full panel, TSH, free T3, and free T4, is necessary because TSH alone can appear normal while free T3 or T4 are suboptimal. Thyroid hormones also interact with GH metabolism and can influence the effectiveness of sermorelin protocols, making baseline thyroid function clinically relevant even when thyroid disease is not the presenting concern.

Metabolic and Safety Markers

The second layer of pre-therapy testing focuses on metabolic health and organ function. These tests do not directly measure hormone axes, but they are essential for establishing safety parameters and identifying conditions that affect both eligibility and monitoring requirements.

Comprehensive Metabolic Panel

The CMP covers kidney function (creatinine, BUN, eGFR), liver enzymes (ALT, AST, alkaline phosphatase, bilirubin), electrolytes, and fasting glucose in a single draw. Liver enzymes provide a safety baseline because some peptides and hormone therapies can affect hepatic enzyme levels, and any changes during therapy are only meaningful if pre-treatment values are documented. Kidney function affects how compounds are metabolized and cleared. Fasting glucose is essential before initiating any GH-stimulating protocol because growth hormone can influence insulin sensitivity.

HbA1c and Fasting Insulin

A single fasting glucose measurement is a snapshot. HbA1c reflects average blood glucose over roughly three months and provides a more complete picture of glucose metabolism. Fasting insulin reveals insulin resistance even when glucose appears normal, because the pancreas can compensate by producing more insulin before glucose levels rise. Insulin resistance is common in adults with age-related hormonal decline and is directly relevant to GH secretagogue protocols. HbA1c above 6.5% indicates diabetes and requires provider assessment before initiating any protocol that affects the GH-insulin axis.

Complete Blood Count

The CBC with differential measures red blood cells, white blood cells, hemoglobin, hematocrit, and platelets. For anyone considering testosterone therapy, hematocrit is a primary safety marker. TRT stimulates red cell production, and if hematocrit rises above 54%, therapy should be paused according to AUA guidelines. Men on testosterone have a documented 3.5-fold higher risk of elevated blood cell counts compared to untreated men, which is why baseline CBC and ongoing monitoring are standard of care rather than optional additions.

Lipid Panel

A complete lipid panel establishes cardiovascular baseline. Both testosterone therapy and GH axis modulation influence lipid metabolism, typically in a favorable direction in appropriately selected patients. The baseline is needed to document those changes accurately, and elevated cardiovascular risk at baseline affects both the appropriateness of certain protocols and the frequency of ongoing monitoring.

PSA for Men Over 40

Prostate-specific antigen testing is recommended for all men over 40 before testosterone therapy as a prostate cancer screen. Both testosterone and GH axis stimulation require prostate safety monitoring. A significantly elevated baseline PSA warrants evaluation before initiating therapy. The American Urological Association notes that approximately 39% of men prescribed TRT nationally do not receive PSA testing beforehand, despite clear guideline recommendations. This is one of the gaps that a thorough provider evaluation is meant to close.

The Complete Checklist

Getting Your Draw Right

Lab results are only as useful as the conditions under which they were collected. Several factors that seem minor can significantly affect readings, and a result that comes back borderline or unexpectedly normal may reflect testing conditions rather than biological reality.

Testosterone and most sex hormones should be drawn between 7 and 10 AM. This is not a guideline preference. The Endocrine Society specifically recommends this window because testosterone peaks in the early morning and can be 20 to 30% lower by early afternoon. A borderline result from an afternoon draw is not a reliable basis for any clinical decision.

Glucose, insulin, HbA1c, and the lipid panel require fasting for 8 to 12 hours. The most practical approach is to schedule a single fasted morning blood draw that captures everything at once. Most hormone tests do not strictly require fasting, but combining them with the metabolic panel in one fasted morning draw is efficient and avoids a second visit.

A few things worth flagging to the lab or provider before drawing: biotin supplementation (common in hair and nail products) can interfere with immunoassay-based hormone tests at high doses; intense exercise within 24 hours can temporarily elevate testosterone and IGF-1; even one night of poor sleep can meaningfully suppress morning testosterone; and a mild illness, even without fever, can produce results that do not reflect the patient’s normal baseline. Testing during any acute stress should be deferred.

What Monitoring Looks Like Once Therapy Starts

Baseline labs are the starting line. Ongoing monitoring at defined intervals is what makes a well-managed protocol actually safe and effective over time. Without it, changes in key markers go undetected, dose adjustments are made on symptoms alone, and contraindications like rising hematocrit or supraphysiological IGF-1 are missed until they become clinical problems.

The standard monitoring schedule in clinical practice follows a straightforward arc. An early safety check at 4 to 6 weeks looks at hematocrit, liver enzymes, and blood pressure where relevant. A full repeat panel at 3 months allows the first objective comparison to baseline, and for GH peptides this is when IGF-1 response becomes visible. Another full panel at 6 months informs protocol optimization. Annual monitoring continues indefinitely for patients who remain on therapy, with PSA included yearly for men on testosterone. The Endocrine Society recommends more frequent initial monitoring with transition to quarterly checks once stable dosing is achieved.

Patients sometimes ask whether they can skip follow-up labs once they feel well. The answer from a clinical standpoint is no. Some of the most clinically significant changes that occur during hormone therapy, rising hematocrit, supraphysiological IGF-1, changes in PSA or liver enzymes, do not produce symptoms until they become problems. The monitoring schedule exists specifically to catch these changes before symptoms appear, not after. For more on how TRT and peptide protocols interact and what the combination monitoring involves, the article Can Peptides Replace TRT? What Men Should Know is a useful resource.