Blood Tests You Should Understand

You go to the doctor, have blood drawn, and a few days later you receive a report filled with numbers, abbreviations, reference ranges, and flags.

Maybe your doctor says, “Everything looks fine.” Maybe one number is marked high or low. Maybe you open the results yourself and have absolutely no idea what you're looking at.

I think you should understand the basics of what these numbers mean. That doesn't mean diagnosing yourself from a laboratory report, and it doesn't mean everybody needs every test available. It means becoming educated enough to have a better conversation about your own health.

Don't just collect numbers. Understand what the numbers are measuring.

Reference Ranges Are Not the Whole Story

Most laboratory reports show your result next to a reference range. That range helps identify results that fall within or outside the laboratory's expected range, but it isn't a perfect dividing line between healthy and unhealthy.

Results need context. Your age, sex, medical history, medications, symptoms, whether you were fasting, other laboratory results, and changes over time can all matter. Different laboratories can also use different methods and reference ranges.

That's why I don't want you looking at one number and immediately deciding, “I'm healthy,” or “Something is terribly wrong.”

A laboratory result is information. Interpretation requires context.

A1C

Hemoglobin A1C, usually shortened to A1C, gives an estimate of your average blood glucose over roughly the previous two to three months, with more recent weeks contributing more to the result.

Unlike a single glucose measurement, A1C gives you a broader picture of glucose exposure over time. It's commonly used in screening for and monitoring diabetes, although certain medical conditions can make A1C less reliable.

If you're working on improving your metabolic health, this can be an important number to understand when it's appropriate for you to have it measured.

Fasting Glucose

Fasting glucose measures the amount of glucose in your blood at a particular point in time after you've gone without calories for the required fasting period.

That's different from A1C. A1C gives you information about longer-term average glucose, while fasting glucose is a snapshot.

Neither number should automatically be interpreted without context. But understanding the difference between them helps you understand why a healthcare professional might look at both.

A1C is a longer-term picture. Fasting glucose is a point-in-time measurement.

Lipids

A lipid panel usually gives you several measurements related to fats and cholesterol in your blood. Instead of looking at the word cholesterol as though it's one number, understand that a lipid panel contains different pieces of information.

Common measurements include total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides. These values can help with cardiovascular-risk assessment, but they shouldn't necessarily be reduced to one number without considering the rest of the person's risk factors.

Triglycerides

Triglycerides are a type of fat circulating in your blood. Their levels can be influenced by factors including diet, alcohol use, metabolic health, certain medications, and genetics.

When you're looking at a lipid panel, don't skip over triglycerides and focus exclusively on total cholesterol. They're another part of the metabolic and cardiovascular picture.

HDL

HDL is commonly called the “good cholesterol.” That's a useful shorthand, but biology is more complicated than simply labeling one cholesterol measurement good and another bad.

Higher HDL levels have historically been associated with lower cardiovascular risk in many populations, but HDL shouldn't be interpreted as a guarantee of protection. It's one measurement within the larger picture.

Don't judge your cardiovascular health from HDL alone.

LDL

LDL cholesterol is one of the major measurements used when assessing cardiovascular risk. Higher LDL levels can contribute to the development of atherosclerotic cardiovascular disease, which is why LDL receives so much attention in medicine.

But the meaning of your LDL result depends on your overall risk. Someone with established cardiovascular disease, diabetes, high blood pressure, smoking history, strong family history, or other risk factors may be evaluated differently from someone without those factors.

Understand the number, but understand the person behind the number too.

Liver Enzymes

Bloodwork may include liver-related measurements such as ALT and AST. These enzymes can become elevated when cells are injured, including in conditions affecting the liver, although they aren't perfectly specific to the liver.

Other measurements may also appear on a liver panel. The important point is that an abnormal liver enzyme doesn't automatically tell you exactly what's wrong, and a normal result doesn't answer every possible question about liver health.

If a result is abnormal, the next question isn't simply, “How do I lower this number?” The better question is:

“Why might this number be abnormal?”

That's something to work through appropriately with your healthcare professional.

Kidney Markers

Common kidney-related measurements include creatinine and an estimated glomerular filtration rate, usually written as eGFR.

Creatinine is a waste product measured in the blood, while eGFR uses information including creatinine to estimate kidney filtration. These numbers can be influenced by factors beyond kidney disease, which is another reason they need to be interpreted in context.

Kidney health may also be evaluated with urine testing, depending on the situation. Again, the point isn't that everybody needs every kidney test. The point is to understand what you're looking at when these measurements appear on your laboratory report.

Thyroid Markers

We already covered thyroid testing in detail in an earlier article, so I'm not going to repeat the entire chapter here.

The main laboratory measurements used when evaluating primary hypothyroidism are typically TSH and free T4. Depending on the circumstances, additional testing such as thyroid antibodies may help answer different questions.

Remember the distinction:

A test can measure thyroid function, help identify the cause of thyroid disease, or investigate a particular clinical situation. Those aren't necessarily the same question.

Don't order every thyroid test you've ever heard about simply because it exists. Testing should have a reason behind it.

Vitamin D

Vitamin D is another measurement you'll commonly hear discussed. Blood vitamin D status is generally evaluated using 25-hydroxyvitamin D, often written as 25(OH)D.

Vitamin D is important for bone and mineral health, but this is another area where more isn't automatically better. A low result may warrant attention, while taking increasingly large amounts of vitamin D simply to chase a higher laboratory number isn't the goal.

The objective isn't to create the most impressive laboratory report. It's to improve your health.

Don't Compare Yourself With Somebody on the Internet

One of the problems with having immediate access to laboratory results is that you can type any number into the internet and find someone telling you exactly what it supposedly means.

Then you find someone with the same A1C, LDL, TSH, or vitamin D result and assume whatever happened to that person must apply to you.

It doesn't work that way.

Your laboratory results belong inside your medical context. Learn what the measurements mean, ask questions, and understand why something is being tested, but don't diagnose yourself by comparing your numbers with a stranger online.

Look at Trends When Trends Matter

Just as one weigh-in doesn't tell the entire story of your weight loss, sometimes one laboratory measurement doesn't tell the entire story of your health.

Suppose a marker is measured more than once over time. Is it improving? Worsening? Staying relatively stable? Was there something different about the circumstances surrounding one test?

Your healthcare professional may care about both the actual result and the pattern over time.

One number is a data point. Multiple appropriate measurements can reveal a trend.

Don't Order Everything Just Because You Can

I don't want this article to become a giant shopping list of blood tests.

More testing isn't automatically better healthcare. Some tests are appropriate as routine screening for certain people. Others are appropriate because of symptoms, medical history, medications, risk factors, or an abnormal result that needs further investigation.

Unnecessary testing can also produce incidental or borderline abnormalities that lead to additional testing without necessarily improving your health.

The question isn't, “How many tests can I get?” The question is, “Which information is actually useful for me?”

Blood Tests and Weight Loss

The scale tells you what you weigh. Your waist tells you something different. Your strength tells you something different. Your laboratory results can tell you something different again.

Someone might lose weight and also see meaningful improvements in glucose-related or other metabolic markers. Those changes may be important even though you can't see them in a progress photo.

That's why the previous chapter emphasized looking beyond the scale.

Your weight is one measurement. Your health is a much bigger picture.

At the same time, don't become obsessed with trying to “optimize” every laboratory number. The purpose of losing excess body fat and improving your lifestyle isn't to turn your life into one giant spreadsheet.

Ask Better Questions

When you receive bloodwork, instead of simply looking for HIGH, LOW, or NORMAL, ask better questions.

What does this test measure? Why was it ordered? Is my result concerning in my particular situation? How does it compare with previous results? Does anything need to change? Does it need to be checked again?

You don't need to become a physician to ask intelligent questions about your own health.

Become an informed participant in your healthcare.

The Simple Rule

Understand the major laboratory markers that are relevant to you without trying to diagnose yourself from individual numbers.

Know what A1C and fasting glucose tell you about glucose regulation. Understand the basic pieces of a lipid panel, including triglycerides, HDL, and LDL. Know why liver enzymes, kidney markers, thyroid markers, and vitamin D might appear on your bloodwork.

But don't assume everybody needs every test, and don't assume that being inside or outside a reference range tells the entire story.

Know what the number measures. Understand the context. Watch meaningful trends. Ask questions when you don't understand something.

Your laboratory report shouldn't just be a page full of mysterious numbers.

Learn what matters, understand what you're measuring, and use that information to make better decisions about your health.

Simple = Success. Commitment = Accountability. Accountability = Results.

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