What Your Lab Results Actually Mean – Part 2

YOUR HEALTH — Issue No. 8

Last week we covered the CBC, CMP, iron, and B12. This week we finish the picture.

These are the tests that drive some of the most important conversations in medicine — cholesterol management, thyroid function, diabetes monitoring, prostate health, and bone density. Most patients get these results back with little explanation.

Lipid Panel

A lipid panel measures the fats circulating in your blood. It is one of the most ordered tests in medicine — and one of the most misunderstood. It consists of a Total cholesterol, LDL, HDL, and Triglycerides.

Total Cholesterol

Total cholesterol is the sum of all cholesterol in your blood. It is the least useful number on your lipid panel in isolation — a high total cholesterol driven by high HDL tells a very different story than the same number driven by high LDL. Never judge a lipid panel by total cholesterol alone.

Normal: below 200 mg/dL is desirable. 200-239 is borderline. 240 and above is high.

LDL — Low Density Lipoprotein

LDL is the primary target of cholesterol treatment. It is the lipoprotein most directly associated with plaque buildup in artery walls — the process that leads to heart attack and stroke.

LDL goals are not one size fits all:

These targets exist because the evidence is clear — the lower the LDL in high risk patients the lower the risk of cardiovascular events. Your goal depends on your risk profile — not just your number.

HDL — High Density Lipoprotein

HDL is often called the good cholesterol. It helps remove cholesterol from artery walls and transport it back to the liver for processing.

Low HDL has long been considered an independent cardiovascular risk factor. However recent research has complicated that picture. Studies have shown that simply raising HDL pharmacologically — through medication — does not reduce cardiovascular risk the way lowering LDL does. Several drugs designed specifically to raise HDL failed in large clinical trials. Current thinking suggests that HDL function may matter more than HDL level — meaning how well it works, not just how much of it is present. For now low HDL remains a marker worth noting but raising it artificially is not the clinical goal it once appeared to be.

Exercise remains the most effective way to raise HDL naturally.

Triglycerides

Triglycerides are fats in your blood derived primarily from dietary carbohydrates and sugars. Elevated triglycerides are associated with cardiovascular risk and are a marker of metabolic dysfunction.

Normal: below 150 mg/dL Borderline: 150-199 mg/dL High: 200-499 mg/dL Very high: 500 mg/dL and above — risk of pancreatitis at this level

The fasting question — what most people get wrong:

Many patients believe fasting significantly affects their entire lipid panel. It doesn't — not equally.

Fasting mainly affects triglycerides. A non-fasting triglyceride reading can be significantly elevated simply from a recent meal — particularly one high in carbohydrates or fat. LDL, HDL, and total cholesterol are relatively stable regardless of fasting status.

This is why many providers now order non-fasting lipid panels for routine screening — the clinically important values are reliable either way. If your triglycerides come back elevated on a non-fasting draw your provider may ask you to repeat the test fasting before acting on it.

TSH and Thyroid Function Tests

The thyroid is a small gland at the base of your neck that produces hormones regulating metabolism, energy, temperature, heart rate, and many other body functions.

TSH — Thyroid Stimulating Hormone

TSH is produced by the pituitary gland — not the thyroid itself. It tells the thyroid how hard to work. Think of TSH as the thermostat and the thyroid as the furnace.

Normal TSH range: approximately 0.4-4.0 mIU/L — though ranges vary slightly by lab and age.

TSH is the best single screening test for thyroid dysfunction. For most patients once thyroid function is stable your provider will monitor TSH alone at regular intervals.

Subclinical dysfunction: Sometimes TSH is mildly outside the normal range while free T4 remains normal and the patient has no symptoms. This is called subclinical hypothyroidism or subclinical hyperthyroidism depending on the direction. The thyroid is technically still functioning but showing early strain. Whether to treat subclinical dysfunction is a nuanced decision that depends on the degree of abnormality, symptoms, age, and other factors — and is worth a direct conversation with your provider.

Free T4 and Free T3

When TSH is abnormal your provider will often add free T4 and sometimes free T3 to understand what the thyroid is actually producing.

Free T4 (thyroxine) is the primary hormone produced by the thyroid. It is converted in the body to the more active T3. A low free T4 with a high TSH confirms hypothyroidism. A normal free T4 with a mildly abnormal TSH may suggest subclinical dysfunction.

Free T3 (triiodothyronine) is the active form of thyroid hormone. It is less commonly ordered but useful in specific situations — particularly when a patient has symptoms of hypothyroidism despite normal TSH and T4, or in monitoring certain thyroid conditions.

TPO Antibodies — Thyroid Peroxidase Antibodies

TPO antibodies are ordered when hypothyroidism is confirmed or suspected — particularly to identify the underlying cause. Elevated TPO antibodies indicate an autoimmune attack on the thyroid.

Hashimoto's thyroiditis is the most common cause of hypothyroidism in the United States — and it is an autoimmune condition. The immune system mistakenly attacks thyroid tissue over time reducing its ability to produce hormone. Elevated TPO antibodies in the setting of hypothyroidism strongly suggest Hashimoto's as the cause.

Causes of hypothyroidism:

One important clinical note:

A single abnormal TSH does not always mean your thyroid is truly dysfunctional. TSH can fluctuate due to acute illness, certain medications, biotin supplementation, time of day variation, and lab error. This is why providers often recheck an abnormal TSH before diagnosing or treating — particularly when the value is only mildly outside the normal range.

A full Plain Medicine deep-dive on thyroid — including what the evidence says about treatment, over-diagnosis, and the questions worth asking your provider — is coming in a future issue.

A1c — Glycated Hemoglobin

The A1c measures your average blood sugar over approximately the past three months. It is the primary tool for diagnosing and monitoring diabetes.

How it actually works — the RBC lifespan explanation:

Red blood cells live approximately 90-120 days. During their lifespan glucose in the bloodstream attaches to hemoglobin — the protein inside red blood cells. The more glucose in the blood the more attaches. The A1c measures the percentage of hemoglobin that has glucose attached.

Because red blood cells live roughly three months — the A1c reflects your average blood sugar over that entire period. A single fasting glucose tells you what your blood sugar is right now. The A1c tells you what it has been doing for the past three months.

A1c ranges:

A1c goals in diabetes:

A healthy 55-year-old with newly diagnosed diabetes and no complications has every reason to pursue tight control — the evidence strongly supports it for reducing long-term complications. An 88-year-old with established heart disease, CKD, and limited life expectancy has a different priority — avoiding hypoglycemia, which in older adults can cause falls, cardiac events, and hospitalization. A slightly higher A1c in that patient is not failure. It is appropriate individualized care.

PSA — Prostate Specific Antigen

PSA is a protein produced by prostate tissue. The PSA test measures the amount of PSA in the bloodstream and is used primarily as a screening tool for prostate cancer and to monitor prostate health over time.

Normal PSA: generally below 4.0 ng/mL — though age-adjusted ranges exist and some providers use lower thresholds.

Why PSA can be elevated — it's not always cancer:

An elevated PSA does not mean prostate cancer. Many conditions raise PSA:

The controversy — why some agencies don't recommend routine PSA screening:

The United States Preventive Services Task Force (USPSTF) recommends shared decision making for PSA screening in men aged 55-69 — meaning the decision should be made individually between patient and provider rather than as a universal recommendation. For men 70 and older the USPSTF recommends against routine screening.

The concern is overdiagnosis — detecting slow-growing prostate cancers that would never cause symptoms or harm during a patient's lifetime, leading to unnecessary treatment with significant side effects including incontinence and erectile dysfunction.

The case for annual trend monitoring:

A single PSA reading is less useful than a trend over time. Establishing a baseline PSA and monitoring it annually allows your provider to detect meaningful change early — before a value crosses an absolute threshold. How a PSA moves over time tells a more complete story than any single number.

One thing worth knowing: if your PSA comes back elevated your provider may order a free PSA — also called percent free PSA — before recommending a biopsy. Total PSA circulates in two forms — bound to proteins and unbound (free). Prostate cancer tends to produce more protein-bound PSA while benign conditions like BPH produce more free PSA. A higher percentage of free PSA suggests a benign cause. A lower percentage increases concern for cancer. This simple additional test can help avoid unnecessary biopsies in men with mildly elevated PSA — and is worth asking about if your PSA comes back abnormal.

PSA after prostatectomy:

Men who have had their prostate removed should have an essentially undetectable PSA after surgery. A rising PSA after prostatectomy is a signal that warrants close monitoring — even in the absence of symptoms. This is why PSA monitoring continues after prostate removal and should never be stopped.

Vitamin D

Vitamin D is less a vitamin than a hormone — it is produced in the skin in response to sunlight and plays a role in calcium absorption, bone health, immune function, and muscle strength.

Vitamin D deficiency is an epidemic.

Studies estimate that over 40% of American adults are deficient in Vitamin D — with rates significantly higher in older adults, darker-skinned individuals, and people who spend limited time outdoors.

Normal 25-OH Vitamin D: 30-100 ng/mL Insufficient: 20-29 ng/mL Deficient: below 20 ng/mL

Sun exposure is the most natural way to produce Vitamin D. Approximately 10-30 minutes of midday sun exposure on the arms and legs several times per week can maintain adequate levels in many people — depending on skin tone, latitude, and season. Darker skin requires longer exposure to produce the same amount of Vitamin D as lighter skin due to higher melanin content.

Sunscreen significantly reduces Vitamin D production — SPF 30 blocks approximately 95% of UV-B rays responsible for Vitamin D synthesis. This doesn't mean avoiding sunscreen — skin cancer risk is real. It means sun exposure and supplementation together are often necessary for people who are diligent about sun protection.

Vitamin D2 vs Vitamin D3 — an important distinction:

Vitamin D3 (cholecalciferol) is the form produced naturally by the skin. It is more effectively absorbed and raises blood Vitamin D levels more efficiently than D2. Available over the counter.

Vitamin D2 (ergocalciferol) is the form most commonly prescribed — typically as a high dose weekly prescription of 50,000 IU. It is less potent than D3 but is prescribed because insurance may cover it as a prescription medication while OTC D3 supplements are not covered.

If you have been on prescription Vitamin D2 and your levels are slow to rise — ask your provider about switching to daily OTC Vitamin D3. For many patients D3 is more effective at achieving and maintaining adequate levels.

Vitamin D and calcium — the connection:

Vitamin D is essential for calcium absorption in the gut. Without adequate Vitamin D your body cannot absorb calcium effectively regardless of how much you consume. This is why Vitamin D deficiency and calcium deficiency often occur together.

The bone health connection:

Chronic Vitamin D deficiency leads to reduced calcium absorption — which the body compensates for by pulling calcium from bones. Over time this contributes to decreased bone mineral density, osteopenia, and osteoporosis — significantly increasing fracture risk.

For patients with osteoporosis or low bone density — correcting Vitamin D deficiency is a foundational step in treatment. Calcium supplementation without adequate Vitamin D is significantly less effective.

The Member deep-dive this week covers advanced lipid testing and whether APO testing is worth the cost, what the cardiovascular risk reduction data actually shows, the full breakdown of TSH fluctuation and why a single abnormal reading is often not what it seems, PSA velocity and doubling time — the numbers behind trend monitoring, biochemical recurrence after prostatectomy in detail, A1c complication risk reduction data, and Vitamin D dosing and osteoporosis management.

Next week: Putting it all together — real patient scenarios showing exactly how a PA thinks through lab results from first complaint to clinical decision.

Plain Medicine is published for educational purposes only and does not constitute medical advice or establish a patient-provider relationship. Always consult your healthcare provider before making medical decisions.

— Kyle