There’s no single “blood level” to track. Your blood carries dozens of measurable substances, and each one has its own healthy range. The most commonly tested values fall into a few categories: blood sugar, cholesterol, vitamins, thyroid hormones, kidney and liver markers, and basic blood cell counts. Here’s what healthy looks like for each, and what the numbers actually mean.
Blood Sugar
Fasting blood sugar is one of the most frequently checked values, and the thresholds are straightforward. A normal fasting level is below 100 mg/dL. Between 100 and 125 mg/dL is considered prediabetes. A reading of 126 mg/dL or higher on two separate tests indicates diabetes.
Your doctor may also check your A1c, which reflects your average blood sugar over the past two to three months rather than a single snapshot. A normal A1c is below 5.7%. Between 5.7% and 6.4% falls into the prediabetes range. At 6.5% or higher, diabetes is diagnosed. If your A1c creeps above 6.0%, your five-year risk of developing diabetes jumps significantly, somewhere between 25% and 50%, so that’s the zone where lifestyle changes make the biggest difference.
Cholesterol and Triglycerides
Cholesterol panels measure several things at once, and the targets differ depending on which type you’re looking at.
- LDL (“bad” cholesterol): Less than 100 mg/dL is the healthy target for most adults.
- HDL (“good” cholesterol): 60 mg/dL or higher is ideal for both men and women. Higher is better here, because HDL helps clear cholesterol from your arteries.
- Triglycerides: Below 150 mg/dL is normal. Triglycerides aren’t cholesterol, but they’re measured on the same panel because elevated levels raise heart disease risk.
Your ideal targets may be stricter if you have a family history of heart disease or other risk factors. Some cardiologists now recommend getting a baseline cholesterol panel in your 30s or 40s, since prevention works best when it starts early.
Vitamin D
Vitamin D is measured as 25-hydroxyvitamin D in your blood, reported in nanograms per milliliter (ng/mL). Below 12 ng/mL is deficiency, which can lead to bone weakening and muscle problems. Between 12 and 20 ng/mL is considered inadequate for bone and overall health. At 20 ng/mL or above, most people have enough vitamin D for their body to function well.
Despite its popularity as a test, most guidelines don’t recommend routine vitamin D screening for healthy people. Testing makes more sense if you have a condition that affects vitamin D absorption, you take medications that lower it, or you have limited sun exposure. The Endocrine Society has specifically recommended against screening in people without risk factors.
Thyroid Function (TSH)
TSH, or thyroid-stimulating hormone, tells you how hard your brain is working to keep your thyroid active. The standard reference range is 0.4 to 5.0 mIU/L, though some experts argue the true healthy range is narrower, closer to 0.4 to 2.5 mIU/L.
A high TSH means your thyroid is underperforming and your brain is sending extra signals to compensate. That can cause fatigue, weight gain, and feeling cold all the time. A low TSH suggests an overactive thyroid, which can cause anxiety, weight loss, and a rapid heartbeat. TSH values also shift with age: older adults naturally run a bit higher without it being a problem.
Hemoglobin and Iron Stores
Hemoglobin measures how much oxygen-carrying protein is in your red blood cells. For men, the normal range is 13.2 to 16.6 grams per deciliter. For women, it’s 11.6 to 15 g/dL. Low hemoglobin is the hallmark of anemia, which causes fatigue, shortness of breath, and dizziness.
Ferritin measures your body’s iron reserves. The range is wide: 24 to 336 micrograms per liter for men, and 11 to 307 for women. A low ferritin level is one of the earliest signs your iron is dropping, often showing up before hemoglobin falls. If you’re experiencing unexplained fatigue, ferritin is worth checking even if your hemoglobin looks normal.
Kidney Function (eGFR)
Your kidneys filter waste from your blood, and the eGFR (estimated glomerular filtration rate) tells you how well they’re doing it. A score of 60 or higher is normal. Below 60 suggests kidney disease. At 15 or lower, the kidneys are failing and can no longer keep up with the body’s needs.
eGFR is calculated from a simple blood test that measures creatinine, a waste product from muscle activity. You won’t feel kidney disease in its early stages, which is why this number matters on routine bloodwork. It’s especially important to track if you have diabetes, high blood pressure, or a family history of kidney problems.
Liver Enzymes
Two liver enzymes show up on most standard panels. ALT normally runs between 7 and 55 units per liter, and AST between 8 and 48 U/L. These enzymes live inside liver cells. When the liver is irritated or damaged, the cells leak more of them into the bloodstream, and the numbers rise.
Mildly elevated levels can come from medications, alcohol, fatty liver, or even intense exercise. Persistently high readings, especially if they’re double or triple the upper limit, signal that something is actively stressing the liver and warrants further investigation.
Electrolytes: Sodium and Potassium
These two minerals control fluid balance, nerve signaling, and heart rhythm. Normal blood sodium is 135 to 145 mEq/L, and normal potassium is 3.5 to 5.0 mEq/L. Both high and low values in either direction can cause problems. Low potassium can trigger muscle cramps and irregular heartbeats. High sodium usually reflects dehydration rather than eating too much salt, since healthy kidneys are good at excreting excess sodium.
How Often to Get Tested
There’s no universal schedule that fits everyone. For cholesterol, a baseline panel in your 30s or 40s gives you and your doctor a reference point to track changes over time. Blood sugar testing becomes more important after age 45, or earlier if you carry extra weight or have a family history of diabetes. A complete blood count is commonly part of an annual physical, and tracking your personal trends over time is more useful than comparing to population averages.
If you’re looking at a lab report and a value falls just outside the reference range, that doesn’t automatically mean something is wrong. Ranges are built from population data, and a single slightly off reading can reflect hydration, timing of your last meal, or normal day-to-day variation. A pattern of abnormal results across multiple tests is far more meaningful than one isolated number.