Laboratory Panels

For physicians

Panel structure

Panels are selected to the clinical question rather than ordered as a block. The available groups include glycemic and insulin markers; inflammatory markers; lipid particle analysis; thyroid; nutrient and mineral status; sex hormones; autoimmune, pulmonary, renal and hepatic panels; and, where specifically indicated, pharmacogenomic and therapeutic drug monitoring.

Why insulin belongs in a screening panel

Hyperinsulinemia maintains euglycemia for years before glucose rises, so a glucose-only panel systematically detects the process late. This is the same argument that runs through the in-office measurements: nerve injury associated with impaired glucose tolerance and metabolic syndrome begins during the compensating phase, and by the time glycemic criteria are met the small-fiber and vascular consequences are already measurable.

In the general adult population, 12.2% of American adults met a full definition of optimal metabolic health in the National Health and Nutrition Examination Survey for 2009 to 2016 — so roughly 88% of US adults did not, using a definition that includes fasting glucose under 100 mg/dL and hemoglobin A1c under 5.7% among its criteria. In the Padda Institute patient population the picture is starker still: fewer than 3% of patients overall, and fewer than 1% of chronic pain patients, meet the same definition of metabolic health. Those are practice-reported figures from our own population, not trial outcomes, and individual results vary.

Ordering discipline

• Fasting state must be documented, not assumed — it changes glucose, insulin, triglycerides and the derived indices.
• Record the draw time. Cortisol, testosterone and thyroid markers all have diurnal variation.
• Do not order autoimmune or genomic panels reflexively. A positive result without a clinical question generates work rather than information.
• Reconcile with recent outside results before duplicating them.

Where it fits

Read against sudomotor testing, endothelial markers and measured metabolic rate. Interpreting the report.

Evidence and limitations

Written for a reader who wants the literature rather than the summary. Where the evidence is thin we say so and give both sides, and where a claim is mechanistic rather than demonstrated we label it as such.

Mechanism

Insulin resistance is compensated before it is decompensated. Beta cells increase secretion to maintain euglycemia, so circulating insulin rises for years while fasting glucose and glycated hemoglobin remain within reference ranges. A panel that measures only glucose therefore detects the process at the point where compensation has already failed. Endothelial signaling is coupled to insulin action in the vessel wall, which is why endothelial and inflammatory markers move with insulin resistance rather than waiting for hyperglycemia.

What the evidence shows

The prevalence data makes the ordering argument concrete. Defining optimal metabolic health as optimal waist circumference, fasting glucose below 100 mg/dL and hemoglobin A1c below 5.7%, blood pressure below 120/80, triglycerides below 150 mg/dL and high-density lipoprotein cholesterol at or above 40 mg/dL in men and 50 mg/dL in women, with no medication for any of them, 12.2% (95% CI 10.9 to 13.6) of American adults met the definition in the 2009–2016 National Health and Nutrition Examination Survey, n=8,721. Under older Adult Treatment Panel III cut points the figure was 19.9% (95% CI 18.3 to 21.5). Fewer than one third of normal-weight adults met it; the proportion fell to 8.0% in overweight adults and 0.5% in adults with obesity.

On the neuropathy side, nerve injury associated with impaired glucose tolerance and metabolic syndrome preferentially affects small fibers and is relatively invisible to nerve conduction studies, which is why the same visit measures small-fiber function directly. Screening guidance from the American Diabetes Association is explicit that assessment should not wait for symptoms and that much distal symmetric polyneuropathy is painless.

Limitations of that evidence

• Cross-sectional prevalence. The survey describes how common a state is, not what happens to the people in it.
• The definition drives the number. Changing the cut points moved the estimate from 19.9% to 12.2% in the same data; removing waist circumference from the definition raised it to 17.6%. Any prevalence figure of this kind is a statement about a criterion as much as about a population.
• Fasting insulin lacks an agreed diagnostic threshold and assay standardization is imperfect between laboratories, which limits comparison of absolute values across sites.
• Diurnal variation affects cortisol, testosterone and thyroid markers, so draw time is part of the result.
• Broad panels generate incidental findings. Autoimmune and genomic panels ordered without a clinical question produce work rather than information.

What remains uncertain

Whether adding fasting insulin to routine screening improves outcomes has not been tested in a randomized trial, and it is not claimed here. The argument for it is mechanistic and temporal — the abnormality precedes the one currently measured — and it is strengthened, not settled, by the observation that small-fiber and vascular consequences are already detectable during the compensating phase. Where a marker cannot be tied to a decision, it is better left unordered.