Which Labs Are Needed Before My Clinical Visit? | Calibrate

Why Pre-Visit Labs Matter for a Metabolic Health Program

Your lab work is the clinical foundation of your Calibrate visit. Without it, the physician cannot safely determine whether a GLP-1 receptor agonist (such as semaglutide or tirzepatide) is appropriate, whether thyroid disease is contributing to weight gain, or whether uncontrolled glucose levels require a modified titration schedule.

The American Thyroid Association notes that thyroid dysfunction is present in approximately 4.6% of the U.S. Population and that subclinical hypothyroidism may be as prevalent as 10% in women over 60, making baseline TSH an essential screening step before attributing weight gain to lifestyle factors alone (ATA, Hypothyroidism Booklet).

Pre-visit labs also protect you. Semaglutide 2.4 mg (Wegovy) carries a boxed warning for a personal or family history of medullary thyroid carcinoma, and the FDA prescribing information specifies that calcitonin and relevant history must be reviewed before prescribing (FDA, Wegovy Prescribing Information).

What Happens If You Arrive Without Labs

Arriving at your clinical visit without completed labs typically delays the prescription by at least one billing cycle. The physician cannot sign off on a GLP-1 prescription without confirmed metabolic baseline data. Some programs will reschedule the consult entirely.

How to Get the Labs Done

Most patients use Quest Diagnostics or LabCorp, both of which accept physician requisition orders generated by the Calibrate platform. Certain states also allow direct-to-consumer lab orders through services such as Labcorp OnDemand. Fasting for 9 to 12 hours before your draw is required for accurate fasting glucose and triglyceride readings.

TSH: The Thyroid Screening Test You Cannot Skip

TSH (thyroid-stimulating hormone) is the single most informative first-line test for thyroid dysfunction. A result outside the 0.4 to 4.0 mIU/L reference range warrants follow-up with free T4 and, in some cases, free T3 before a GLP-1 is prescribed.

The reason TSH matters specifically for a weight-loss program is direct: hypothyroidism slows basal metabolic rate, raises LDL cholesterol, and causes weight gain that will not respond to GLP-1 therapy until the thyroid condition is treated. The 2012 American Thyroid Association guidelines state: "Patients with overt hypothyroidism should be treated with levothyroxine to normalize serum TSH before initiating other weight-management interventions." (ATA 2012 Guidelines for Hypothyroidism)

TSH Results and What They Indicate

| TSH Value | Interpretation | Typical Next Step | |---|---|---| | 0.4 to 4.0 mIU/L | Normal | Proceed with program | | 4.1 to 10.0 mIU/L | Subclinical hypothyroidism | Free T4 reflex; consider levothyroxine | | <0.4 mIU/L | Possible hyperthyroidism | Free T4, free T3, TSI ordered | | >10.0 mIU/L | Overt hypothyroidism | Treat before GLP-1 initiation |

A 2017 analysis published in Thyroid (N=4,082) found that subclinical hypothyroidism was associated with a 1.5-fold increased risk of metabolic syndrome components, reinforcing why correcting TSH before adding a GLP-1 agent improves net outcomes (PMID 28278630).

Free T4 and Free T3: When Are They Added?

Free T4 is reflexively ordered when TSH is abnormal. Free T3 is added when hyperthyroidism is suspected or when a patient reports persistent symptoms despite a normal TSH, a scenario more common in patients with Hashimoto's thyroiditis who are already on levothyroxine. Thyroid peroxidase antibody (TPO Ab) testing may be added if autoimmune thyroid disease is clinically suspected.

Fasting Glucose and HbA1c: Metabolic Eligibility Checkpoints

Fasting plasma glucose and glycated hemoglobin (HbA1c) serve two distinct purposes: they confirm whether a patient meets metabolic eligibility criteria and they identify contraindications or dose-modification scenarios.

The American Diabetes Association classifies fasting glucose ≥126 mg/dL on two occasions or HbA1c ≥6.5% as diagnostic for type 2 diabetes (ADA Standards of Care 2024). A patient with HbA1c >10% may need additional endocrine evaluation before starting a GLP-1, since uncontrolled hyperglycemia at that level often indicates insulin deficiency rather than insulin resistance and warrants a different treatment approach.

Why Fasting Glucose Requires a 9-to-12-Hour Fast

Even a 4-hour partial fast can lower postprandial glucose enough to push a borderline result into the normal range, masking prediabetes. The CDC defines prediabetes as fasting glucose of 100 to 125 mg/dL and notes that 96 million American adults, or roughly 38% of the U.S. Adult population, have prediabetes (CDC, National Diabetes Statistics Report 2022).

HbA1c as a 90-Day Average

HbA1c reflects average plasma glucose over approximately 90 days and does not require fasting. It is less affected by day-to-day glucose fluctuations. For a weight-loss program, HbA1c is particularly useful because it captures the metabolic picture across the weeks before the visit, not just the morning of the blood draw.

In the STEP-1 trial (N=1,961), semaglutide 2.4 mg produced a mean weight loss of 14.9% at 68 weeks versus 2.4% for placebo (P<0.001), with the most pronounced metabolic improvements seen in participants who had baseline HbA1c between 5.7% and 6.4% (prediabetes range) (NEJM, Wilding et al. 2021).

Lipid Panel: Cardiovascular Risk Stratification Before Prescribing

A fasting lipid panel includes total cholesterol, LDL, HDL, and triglycerides. For Calibrate's clinical team, this panel serves two purposes. First, it establishes cardiovascular baseline risk, since GLP-1 receptor agonists are now indicated for cardiovascular risk reduction in patients with established cardiovascular disease or high-risk type 2 diabetes. Second, markedly elevated triglycerides (above 500 mg/dL) raise the risk of acute pancreatitis, a listed adverse effect of semaglutide.

The SELECT trial (N=17,604) demonstrated that semaglutide 2.4 mg reduced major adverse cardiovascular events by 20% in adults with overweight or obesity and established cardiovascular disease, with no prior diabetes required for eligibility (NEJM, Lincoff et al. 2023).

What Lipid Values Require Attention

| Marker | Value of Concern | Clinical Action | |---|---|---| | LDL | >190 mg/dL | Evaluate for familial hypercholesterolemia | | Triglycerides | >500 mg/dL | GLP-1 initiation deferred; pancreatitis risk | | HDL | <40 mg/dL (men) / <50 mg/dL (women) | Lifestyle counseling intensified | | Total cholesterol | >240 mg/dL | 10-year ASCVD risk calculated |

The American Heart Association's 2019 guidelines recommend a risk-based approach to lipid management that incorporates statin therapy alongside lifestyle modification for patients with LDL ≥70 mg/dL and high 10-year ASCVD risk (AHA/ACC 2019 Guideline).

Comprehensive Metabolic Panel: Kidney and Liver Clearance

The comprehensive metabolic panel (CMP) includes 14 markers: sodium, potassium, chloride, bicarbonate, BUN, creatinine, eGFR, glucose, calcium, total protein, albumin, total bilirubin, alkaline phosphatase, AST, and ALT.

For GLP-1 prescribing, the two subgroups of most concern are kidney function and liver enzymes.

Kidney Function: eGFR and Creatinine

Semaglutide does not require dose adjustment for mild-to-moderate chronic kidney disease (CKD), but the FDA labeling recommends monitoring renal function in patients who experience severe GI side effects leading to dehydration (FDA, Ozempic Prescribing Information). An eGFR <30 mL/min/1.73m² (Stage 4 to 5 CKD) generally triggers specialist co-management before initiating a GLP-1.

Liver Enzymes: ALT and AST

Elevated transaminases may indicate non-alcoholic fatty liver disease (NAFLD), which is present in an estimated 25% of the global population and strongly associated with insulin resistance (PMID 26707365). GLP-1 receptor agonists have shown benefit in NAFLD, but a baseline ALT greater than 3 times the upper limit of normal requires hepatic evaluation before prescribing.

CBC: Ruling Out Anemia and Other Hematologic Causes of Fatigue

A complete blood count (CBC) checks red blood cells, white blood cells, hemoglobin, hematocrit, and platelet count. Iron-deficiency anemia produces fatigue and cold intolerance that closely mimic hypothyroidism. Identifying anemia at baseline prevents misattribution of symptoms and guides supplementation that could otherwise mask a dietary deficiency worsened by GLP-1-related reduced appetite.

The NIH Office of Dietary Supplements reports that iron deficiency is the most common nutritional deficiency worldwide, affecting an estimated 2 billion people, with pre-menopausal women at highest risk (NIH ODS, Iron Fact Sheet). Hemoglobin <12 g/dL in women or <13 g/dL in men warrants iron studies (serum ferritin, TIBC) before finalizing a program plan.

Additional Markers Sometimes Requested

Depending on your personal history, the Calibrate physician may add markers beyond the standard panel.

Insulin and HOMA-IR

Fasting insulin, combined with fasting glucose, allows calculation of HOMA-IR (Homeostatic Model Assessment of Insulin Resistance). A HOMA-IR score above 2.0 is commonly used as a threshold for clinically meaningful insulin resistance, though reference ranges vary by laboratory. This calculation is particularly informative in patients with normal HbA1c but strong clinical suspicion of metabolic dysfunction.

Vitamin D (25-OH)

Vitamin D deficiency is associated with insulin resistance and may worsen obesity-related inflammation. A 2014 meta-analysis in Obesity Reviews (28 studies, N=99,745) found that each 10 ng/mL increase in serum 25(OH)D was associated with a 4.2% lower risk of developing type 2 diabetes (PMID 24450950). The Endocrine Society defines sufficiency as 25(OH)D ≥30 ng/mL (Endocrine Society Clinical Practice Guideline).

Uric Acid

Hyperuricemia is independently associated with insulin resistance and metabolic syndrome. Rapid weight loss, including that induced by GLP-1 therapy, can transiently raise uric acid levels, making a baseline value clinically useful for patients with a history of gout.

HealthRX Pre-Visit Lab Decision Framework

The table below summarizes which add-on tests to request based on personal history. Use it when placing your lab order.

| Personal History | Add-On Test | |---|---| | Prior thyroid disease or medication | Free T4, TPO Ab | | Polycystic ovary syndrome (PCOS) | Fasting insulin, HOMA-IR, testosterone | | Fatigue, joint pain, hair loss | Vitamin D, ferritin, B12 | | History of gout | Uric acid | | Unexplained elevated TSH on prior labs | Anti-TPO, anti-thyroglobulin Ab | | Liver disease or heavy alcohol use | GGT, full hepatic function panel | | Family history of MTC or MEN2 | Calcitonin (required per semaglutide labeling) |

Timing, Fasting, and Logistics

When to Schedule Your Blood Draw

Schedule your blood draw at least 5 business days before your clinical visit. Most Quest and LabCorp locations release results to your ordering portal within 24 to 72 hours, but flagged values may trigger a hold for physician review before your appointment proceeds. Giving yourself 5 days creates buffer for repeat draws if a sample is hemolyzed or a value requires confirmation.

Fasting Protocol

Fast for 9 to 12 hours before your draw. Water, black coffee, and plain tea without additives are generally acceptable. Avoid strenuous exercise the morning of your draw, since acute exercise can transiently raise ALT, AST, glucose, and creatinine, all markers on your panel.

Medications on the Day of the Draw

Do not skip your regular morning medications. Thyroid hormone (levothyroxine) should be taken at your normal time. Metformin and statins should continue as prescribed. If you take biotin supplements at doses above 5 mg/day, stop them 48 to 72 hours before the draw, as high-dose biotin interferes with immunoassays used for TSH measurement, potentially producing a falsely low TSH result (FDA Safety Communication on Biotin, 2019).

What the Physician Reviews at Your Visit

Your Calibrate physician will review the full panel against your reported symptoms, BMI, blood pressure, and personal and family history. The clinical visit is not simply a checkbox exercise. The physician integrates your lab picture to determine:

1. Whether a GLP-1 is safe to initiate immediately
2. Which starting dose is appropriate (e.g., semaglutide 0.25 mg weekly titration vs. Tirzepatide 2.5 mg weekly)
3. Whether any values require treatment or specialist referral before or alongside GLP-1 therapy
4. Which markers to recheck at your 3-month follow-up visit

A 2022 position statement from the American Association of Clinical Endocrinology recommends a structured metabolic panel at baseline and at 3-month intervals for all patients on GLP-1 receptor agonist therapy, with particular attention to HbA1c, lipids, and renal function (AACE 2022 Obesity Clinical Practice Guidelines).