Lab Test Guide
By the UnitedWellness editorial team · 8 min read
Most people get lab work done and then stare at a page full of numbers, flags, and abbreviations with little idea of what any of it means. The reference ranges help, but they don’t tell you when a result is clinically meaningful versus a statistical blip. This guide explains what you’re actually looking at.
How to read a lab report
A standard lab report shows three things for each test: your result, the reference range, and sometimes a flag (H for high, L for low) if your result falls outside that range. The reference range is the key context you need.
Reference ranges are calculated from population data - specifically, they represent the range within which approximately 95% of healthy adults fall. This means that by statistical definition, about 5% of healthy people will have a result outside the reference range for any given test. A single flagged result in an otherwise normal panel may not be clinically meaningful. Multiple flagged results, or results significantly outside range, warrant more attention.
The reference range also varies by lab, by the population the lab used to establish its norms, and sometimes by age and sex. Two labs can run the same test on the same blood sample and report slightly different reference ranges. This is normal and expected.
Common markers and what they mean
Metabolic panel
Glucose - measures blood sugar at a point in time. Fasting glucose above 100 mg/dL is considered prediabetic range; above 126 mg/dL on two tests is diagnostic for diabetes. Values fluctuate with recent meals, stress, and activity.
HbA1c - reflects average blood sugar over the past 2 to 3 months. More useful than a single glucose reading for understanding metabolic health trends. Below 5.7% is normal; 5.7–6.4% is prediabetic range.
Insulin - fasting insulin above 10 µIU/mL is increasingly recognized as a meaningful signal for insulin resistance, even when fasting glucose appears normal. Not always included in standard panels.
Lipid panel
Total cholesterol - context-dependent. High total cholesterol alone is a poor predictor of cardiovascular risk without knowing the composition.
LDL cholesterol - the standard “bad cholesterol” marker. Standard care aims for below 100 mg/dL in most adults, lower in those with cardiovascular risk.
HDL cholesterol - generally, higher is better. Below 40 mg/dL in men or 50 mg/dL in women is considered a risk factor.
Triglycerides - strongly influenced by diet and carbohydrate intake. Below 150 mg/dL is normal; above 200 mg/dL is elevated.
ApoB - measures the number of atherogenic (plaque-forming) particles rather than the weight of cholesterol. Increasingly recognized as a more informative cardiovascular risk marker than LDL alone. Not always included in standard panels.
Inflammation markers
hs-CRP (high-sensitivity C-reactive protein) - a general marker of systemic inflammation. Below 1.0 mg/L is low risk; 1.0–3.0 mg/L is moderate; above 3.0 mg/L is elevated. Rises with illness, injury, and stress - a single elevated reading should be repeated before drawing conclusions.
Homocysteine - elevated levels (above 15 µmol/L) are associated with cardiovascular and cognitive risk. Responsive to B vitamin supplementation in many cases. Not included in standard panels but available at additional cost or through comprehensive testing services.
Thyroid
TSH (thyroid-stimulating hormone) - the primary screening test for thyroid function. High TSH suggests an underactive thyroid; low TSH suggests an overactive thyroid. Standard reference range is roughly 0.5–4.5 mIU/L, though some providers use narrower ranges for optimal function.
Free T3 and Free T4 - the active thyroid hormones. Often added when TSH is abnormal or symptoms suggest thyroid dysfunction despite a normal TSH.
Hormones
Testosterone (total and free) - reference ranges are age-dependent and vary significantly by lab. Free testosterone is often more clinically meaningful than total, but many standard panels only report total. Time of day matters - testosterone is highest in the morning; draw before 10 AM for most accurate results.
Estradiol and progesterone - vary significantly by phase of menstrual cycle and menopausal status. Results require cycle-phase context to interpret correctly.
DHEA-S - an adrenal androgen that declines with age. Low levels are associated with fatigue and decreased libido in both men and women.
Reference range vs. optimal range
Preventive testing services like Function Health and InsideTracker report results against both standard reference ranges and what they call “optimal” or “InnerAge” ranges - levels associated with better long-term outcomes rather than just the absence of disease. These tighter ranges will flag more results as suboptimal.
This approach is useful for proactive health management but can also create anxiety about results that are technically within normal range. The distinction matters: a result in the standard reference range but flagged by a preventive testing service’s “optimal” algorithm is an area to monitor and discuss with your provider, not necessarily a diagnosis or an emergency.
When to follow up with a provider
Follow up when: a result is significantly outside the reference range (not just slightly), multiple related markers are flagged in the same direction, a result is abnormal on two consecutive tests, or you have symptoms that correlate with an abnormal result.
Don’t panic over: a single mildly flagged result, especially H or L on a panel where everything else looks normal. A single reading in the absence of symptoms often reflects normal variation, collection timing, or dietary factors. Repeat testing is often more informative than a single data point.
See our lab testing services comparison for a full breakdown of at-home testing options and our biomarker guide for a deep dive on which markers matter most for longevity-focused testing.