“Blood levels” covers a wide range of tests, and the numbers your doctor checks depend on what they’re looking for. The most common blood work includes blood sugar, cholesterol, blood cell counts, kidney and liver function, thyroid hormones, and key vitamins and minerals. Here’s what healthy ranges look like for each.
One important note before diving in: reference ranges can vary slightly between labs because different facilities use different testing methods. The numbers printed on your lab report are the ones to compare your results against. The ranges below reflect widely accepted standards and will help you understand what your results mean.
Blood Sugar (Glucose and A1C)
Blood sugar is one of the most frequently tested values, used to screen for prediabetes and diabetes. Two main tests measure it: fasting blood glucose (a snapshot of your blood sugar right now) and A1C (an average of your blood sugar over the past two to three months).
For A1C, the ranges break down clearly:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
To put those percentages into practical terms, an A1C of 6% corresponds to an average blood sugar of about 126 mg/dL. An A1C of 7% means an average around 154 mg/dL, and by 9% you’re looking at an average of 212 mg/dL. If you already have diabetes, your A1C is the number your care team watches most closely to see how well your blood sugar is being managed over time.
Cholesterol and Triglycerides
A lipid panel measures several types of fat in your blood. For adults 20 and older, healthy levels look like this:
- Total cholesterol: less than 200 mg/dL
- LDL (“bad” cholesterol): less than 100 mg/dL
- HDL (“good” cholesterol): 60 mg/dL or higher is ideal. Below 40 mg/dL for men or below 50 mg/dL for women is considered low.
- Triglycerides: below 150 mg/dL
LDL is the number most tied to heart disease risk, so it gets the most attention. HDL works in your favor by helping clear cholesterol from your arteries, which is why higher is better. Triglycerides tend to rise with diets high in sugar and refined carbohydrates, and elevated levels add to your overall cardiovascular risk.
Blood Cell Counts (CBC)
A complete blood count, or CBC, is one of the most routine blood tests. It measures your red blood cells, white blood cells, and platelets. The values doctors focus on most are hemoglobin (the protein in red blood cells that carries oxygen) and white blood cell count (a marker of immune function and infection).
Healthy hemoglobin levels differ by sex:
- Men: 13.2 to 16.6 grams per deciliter
- Women: 11.6 to 15.0 grams per deciliter
Hemoglobin below these ranges can indicate anemia, which often causes fatigue, weakness, and shortness of breath. White blood cell counts normally fall between about 3.4 and 9.6 billion cells per liter. A count above that range can signal infection or inflammation, while a count below it may mean your immune system is suppressed.
Kidney Function
Your kidneys filter waste from your blood, and two numbers tell you how well they’re doing the job: creatinine and GFR (glomerular filtration rate). Creatinine is a waste product from normal muscle activity. When your kidneys aren’t filtering efficiently, creatinine builds up.
Normal creatinine ranges:
- Men: 0.74 to 1.35 mg/dL
- Women: 0.59 to 1.04 mg/dL
Your lab will also calculate a GFR score from your creatinine level. A GFR of 60 or above is generally considered normal. A score below 60 suggests some degree of kidney disease, and the lower the number, the less effectively your kidneys are filtering. This score matters more than creatinine alone because it accounts for factors like age and body size.
Thyroid Function (TSH)
TSH, or thyroid-stimulating hormone, is the standard screening test for thyroid problems. Your brain releases TSH to tell your thyroid gland to produce hormones that regulate metabolism, energy, and body temperature. The typical reference range for adults falls between roughly 0.5 and 4.5 mIU/L, with most healthy people landing between 1.0 and 1.5 mIU/L.
A TSH above the upper limit suggests your thyroid is underactive (hypothyroidism), meaning your brain is working harder to stimulate a sluggish thyroid. A TSH below the lower limit suggests an overactive thyroid (hyperthyroidism). Symptoms of an underactive thyroid include fatigue, weight gain, and feeling cold, while an overactive thyroid can cause weight loss, anxiety, and a rapid heartbeat.
Electrolytes: Sodium and Potassium
Electrolytes keep your nerves, muscles, and heart functioning properly. The two most commonly tested are sodium and potassium.
- Sodium: 135 to 145 mEq/L
- Potassium: 3.5 to 5.0 mEq/L
Sodium levels outside the normal range can cause confusion, headaches, or in severe cases, seizures. Potassium is especially important for heart rhythm. Levels that are too high or too low can cause dangerous irregular heartbeats, which is why potassium is monitored closely in people taking certain blood pressure medications.
Vitamin D
Vitamin D is measured through a blood test that checks your 25-hydroxyvitamin D level. The thresholds are straightforward:
- Sufficient: above 30 ng/mL
- Insufficient: 12 to 30 ng/mL
- Deficient: below 12 ng/mL
Vitamin D deficiency is extremely common, particularly in people who live in northern latitudes, have darker skin, or spend most of their time indoors. Low levels are linked to bone weakness, fatigue, and muscle pain. Many people with levels in the “insufficient” range don’t notice obvious symptoms but may benefit from supplementation, especially during winter months.
Iron Stores (Ferritin)
Ferritin measures how much iron your body has stored away. It’s different from a simple iron test because it reflects your reserves, not just what’s circulating right now. Normal ranges:
- Men: 24 to 336 micrograms per liter
- Women: 11 to 307 micrograms per liter
Low ferritin is the hallmark of iron deficiency and often shows up before your hemoglobin drops enough to qualify as full-blown anemia. Symptoms of low iron stores include persistent fatigue, brain fog, hair thinning, and feeling cold. Women who menstruate are at higher risk because of monthly blood loss.
Which Tests Require Fasting
Some blood tests need you to fast for 8 to 12 hours beforehand, meaning nothing but plain water. The tests that typically require fasting include blood glucose, a lipid panel (cholesterol and triglycerides), and a basic metabolic panel. Liver and kidney function tests sometimes require fasting as well, depending on your provider’s instructions. If you eat before a fasting test, the results may come back artificially high, particularly for blood sugar and triglycerides.
How to Read Your Lab Report
When you get your results, each value will appear alongside a reference range specific to that lab. Results flagged as “H” (high) or “L” (low) fall outside the lab’s expected range. A single out-of-range value doesn’t always mean something is wrong. Dehydration, a recent meal, intense exercise, or even the time of day can shift certain numbers temporarily. What matters more is the pattern: results that are consistently out of range, or that are trending in one direction over time, carry more clinical significance than a one-time blip.
Because different labs use different testing methods, you can’t reliably compare results from one lab to another. If you’re tracking a value over time, try to use the same lab and the same test for consistency.