What lab tests measure and why your doctor orders them

A lab test takes a sample of your blood, urine, or other body fluid and measures what is in it. The results tell your doctor whether something is working the way it should—your kidneys, liver, heart, blood sugar, cholesterol, or how fast your blood clots. Most seniors have at least one lab test a year as part of a checkup. Some tests screen for disease before you feel sick. Others check whether a medicine you are taking is working or causing harm.

Lab tests are not the same as imaging (like X-rays or ultrasounds) or procedures where a doctor looks inside your body. A lab test is usually quick—often just a blood draw—and the results come back in days or sometimes hours.

Key Takeaways

  • Common lab tests for seniors measure blood sugar, cholesterol, kidney function, liver function, and how fast blood clots.
  • Your doctor orders tests based on your age, medical history, medicines you take, and symptoms you report.
  • Blood tests require a small sample drawn from your arm; urine tests use a sample you provide in a cup.
  • Results are usually ready within a few days, and your doctor will explain what they mean and whether you need to change anything.
  • Ask your doctor why a test is being ordered and what the results will be used for if you are unsure.

Common lab tests for seniors

Complete Blood Count (CBC) measures red blood cells, white blood cells, and platelets. It can show whether you have anemia (too few red blood cells), infection, or a bleeding disorder. This is one of the most common tests ordered during a checkup.

Basic Metabolic Panel (BMP) checks kidney function, liver function, blood sugar, and electrolytes (sodium, potassium, and other minerals your body needs). Your doctor uses this to make sure your kidneys and liver are handling waste the way they should and that your blood chemistry is balanced.

Lipid Panel measures cholesterol and triglycerides (a type of fat in your blood). High cholesterol raises your risk of heart attack and stroke. This test is usually done after you have fasted (not eaten) for 9 to 12 hours.

Hemoglobin A1C shows your average blood sugar over the past two to three months. It screens for diabetes and helps your doctor see whether diabetes medicines or diet changes are working. Unlike a single blood sugar reading, this test does not require fasting.

Thyroid Stimulating Hormone (TSH) checks whether your thyroid is working correctly. An underactive thyroid can cause fatigue, weight gain, and depression. An overactive thyroid can cause weight loss, anxiety, and heart problems.

Urinalysis examines urine for signs of kidney disease, urinary tract infection, diabetes, or blood in the urine. You provide a sample in a cup, and the lab checks it with a dipstick and under a microscope.

Why your doctor orders specific tests

Your doctor does not order every possible test at every visit. Instead, the choice depends on your age, your medical history, any symptoms you mention, and medicines you are taking. For example, if you take a blood thinner, your doctor will order a test called PT/INR to make sure the dose is right. If you take a statin for cholesterol, your doctor may order liver function tests to make sure the medicine is not harming your liver.

Screening tests are ordered when you have no symptoms but your doctor wants to catch disease early. A 65-year-old with no history of diabetes might have an A1C test as part of a routine checkup. Someone with a family history of kidney disease might have kidney function tests more often than someone without that risk.

If you are sick or have new symptoms, your doctor may order tests to figure out what is wrong. A test result can also lead to more tests. For example, if your kidney function is low, your doctor might order an ultrasound to look at your kidneys more closely.

How lab tests are done and what to expect

Most lab tests for seniors are blood tests. A nurse or technician will ask you to sit in a chair, tie a band around your upper arm, and insert a needle into a vein. The needle stays in for only a few seconds while blood fills a tube or tubes. You may feel a pinch or slight sting. Some people feel lightheaded, but this passes quickly. The whole process usually takes less than five minutes.

For some tests, you will be asked to fast beforehand—usually for 9 to 12 hours. This means no food or drink except water. Your doctor will tell you if fasting is needed when the test is scheduled. If you forget and eat anyway, tell the lab staff before they draw blood, because some results are not reliable if you have eaten.

Urine tests are simpler. You provide a sample in a cup in a bathroom at the lab or doctor's office. For some urine tests, you may be asked to collect urine over 24 hours at home and bring it to the lab.

After the test, you can usually go about your day. Some people have a small bruise where the needle went in, but this fades in a few days. If you feel dizzy or faint after a blood draw, sit down and tell a staff member.

Understanding your lab results

Lab results come with a number and a range called the "reference range" or "normal range." Your result is compared to this range. If your number is within the range, it is usually considered normal. If it is outside the range, it may be high or low, and your doctor will explain what that means for you.

The reference range is not the same as a target for you personally. For example, a cholesterol level of 200 is within the normal range for most people, but your doctor might want yours lower if you have heart disease. Conversely, a result that is slightly outside the range might not mean anything is wrong—it might just be how your body works, or the result might be affected by medicine you take, food you ate, or stress.

Your doctor will contact you with results and explain what they mean. If a result is concerning, your doctor will tell you what to do next—whether that is a change in medicine, a change in diet or exercise, more tests, or a referral to a specialist. Do not assume a result is bad just because you have not heard from your doctor; many labs report normal results automatically, and your doctor may not call unless something needs to change.

Questions to ask your doctor about lab tests

Before a test is done, you can ask your doctor why it is being ordered and what the results will be used for. Ask whether you need to fast or stop taking any medicines beforehand. Ask when results will be ready and how you will find out about them—by phone, email, patient portal, or at your next visit.

If a result comes back abnormal, ask your doctor what it means, whether you need more tests, and what changes (if any) you should make. Ask whether the result could be caused by a medicine you are taking or something else that is not serious. If your doctor recommends a big change—like starting a new medicine or a strict diet—ask what the goal is and how you will know whether it is working.

If you do not understand an explanation, ask your doctor to explain it a different way or to write it down. Lab results can be confusing, and your doctor should be willing to take time to help you understand.

When lab tests are repeated and what changes mean

Some lab tests are done once a year as part of a routine checkup. Others are done more often if you have a chronic condition like diabetes or heart disease. If you start a new medicine, your doctor may order tests a few weeks later to see how your body is handling it.

A change in your results from one test to the next can be important. For example, if your kidney function drops from one year to the next, your doctor may adjust your medicines or order more tests. If your cholesterol goes down after you started a statin, that shows the medicine is working. Small changes from test to test are usually not a concern—lab results can vary slightly depending on the time of day, what you ate, how much water you drank, and stress.

Keep a record of your lab results if you can. Many doctor's offices have patient portals where you can see your results online. If you see a new doctor, bring your old results so they can see your health history and whether anything has changed over time.

Frequently Asked Questions

Do I need lab tests if I feel fine?

Yes. Many serious conditions like high blood pressure, high cholesterol, diabetes, and kidney disease have no symptoms in the early stages. Lab tests can catch these before you feel sick, when treatment is easier and more effective. Your doctor will recommend screening tests based on your age and risk factors.

Can I eat or drink before a blood test?

It depends on the test. Some tests require fasting (no food or drink except water for 9 to 12 hours). Others do not. Your doctor will tell you when you schedule the test. If you are unsure, call the lab or doctor's office before you go.

What if my result is slightly outside the normal range?

A result just outside the range is not always a sign of disease. It could be caused by medicine you take, stress, dehydration, or just normal variation in your body. Your doctor will look at your result along with your symptoms, medical history, and other tests to decide whether anything needs to change.

How long does it take to get lab results?

Most routine lab tests come back within one to three days. Some results are ready the same day. Your doctor will tell you when to expect results and how you will be notified. If you have not heard anything after a week, call your doctor's office to check.

Do I need to stop my medicines before a lab test?

Usually no. In fact, stopping a medicine without your doctor's permission can be dangerous. Tell the lab and your doctor what medicines you take, because some can affect test results. Your doctor will tell you if any medicine needs to be stopped before a specific test.