Understanding Laboratory Tests: 10 Commonly Used Blood Tests for Older Adults

In this article, I’ll address a real mainstay of modern medicine: laboratory tests that require drawing blood.

This is sometimes referred to as “checking labs,” “doing bloodwork,” or even “checking blood.”

Most older adults have been through this. For instance, it’s pretty much impossible to be hospitalized without having bloodwork done, and it’s part of most emergency room care. Such testing is also often done as part of an annual exam, or “complete physical.”

Last but not least, blood testing is usually — although not always — very helpful when it comes to evaluating many common complaints that affect aging adults.

Fatigued and experiencing low energy? We should perhaps check for anemia and thyroid problems, among other things.

Confused and delirious? Bloodwork can help us check on an older person’s electrolytes (they can be thrown off by a medication side-effect, as well as by other causes). Blood tests can also provide us with information related to infection, kidney function, and much more.

Like much of medical care, blood testing is probably overused. But often, it’s an appropriate and an important part of evaluating an older person’s health care concerns. So as a geriatrician, I routinely order or recommend blood tests for older adults.

Historically, laboratory results were reviewed by the doctors and were only minimally discussed with patients and families. But today, it’s becoming more common for patients to ask questions about their results, and otherwise become more knowledgeable about this aspect of their health.

In fact, one of my top recommendations to older adults and family caregivers is to always request a copy of your laboratory results. (And then, keep it in your personal health record!)

This way, if you ever have questions about your health, or need to see a different doctor, you’ll be able to quickly access this useful information about yourself.

In this article, I’m going to list and briefly explain the blood tests that are most commonly used, for the primary medical care of older adults.

Specifically, I’ll cover four “panels” which are commonly ordered, and then I’ll list six more blood tests that I find especially useful.

In other words, we’re going to cover my top ten blood tests for the healthcare of aging adults.

I’ll finish with some practical tips for you to keep in mind, when it comes to blood tests.

4 common “panels” in laboratory blood testing

1. Complete Blood Count (CBC)

What it measures: A CBC is a collection of tests related to the cells in your blood.  It usually includes the following results:

• White blood cell count (WBCs): the number of white blood cells per microliter of blood
• Red blood cell count (RBCs): the number of red blood cells per microliter of blood
• Hemoglobin (Hgb): how many grams of this oxygen-carrying protein per deciliter of blood
• Hematocrit (Hct): the fraction of blood that is made up of red blood cells
• Mean corpuscular volume (MCV): the average size of red blood cells
• Platelet count (Plts): how many platelets (a smaller cell involved in clotting blood) per microliter of blood

The CBC can also be ordered “with differential.” This means that the white blood cells are classified into their subtypes. For more information on the CBC test, see Medline: CBC blood test. For details on the white blood cell count differential, and what the results might signify, see Medline: Blood differential test.

What the CBC is often used for:

• Anemia may be diagnosed if the red blood cell count, hemoglobin, and hematocrit are lower than normal.
  • I explain anemia in more depth here: Anemia in the Older Adult: 10 Common Causes & What to Ask.
• The white blood cell count usually goes up if a person is fighting an infection. Some medications, such as corticosteroids, can also cause an increase in the white blood cell count.
• If several types of blood cells (i.e. red blood cells, white blood cells, and platelets) are low, this can be a sign of a problem with the bone marrow.
• Occasionally an older person’s platelet count may be lower than normal (or even higher than normal). This usually requires further evaluation.

2. Basic metabolic panel (basic electrolyte panel)

What it measures: Although it’s possible to request a measurement of a single electrolyte, it’s far more common for electrolytes to be ordered as part of a panel of seven or eight measurements. This is often referred to as a “chem-7,”  and usually includes:

• Sodium 
• Potassium 
• Chloride
• Carbon dioxide (CO2) (sometimes referred to as “bicarbonate,” as this is the chemical form of carbon dioxide which is more common in the bloodstream)
• Blood urea nitrogen (BUN)
• Creatinine (often accompanied by an estimated “glomerular filtration rate,” or “eGFR”result)
• Glucose

What the basic metabolic panel is often used for:

• Medication side-effects can cause electrolytes such as sodium or potassium to be either too high or too low.
  • These electrolytes are often monitored when people take certain types of medications, such as certain blood pressure medications, or diuretics.
• Carbon dioxide levels reflect the acidity of the blood.
  • This can be affected by kidney function and by lung function. Severe infection can also change acid levels in the blood.
• Creatinine and BUN levels are most commonly used to monitor kidney function. Both of these measurements can go up if kidney function is temporarily impaired (e.g. by dehydration or a medication side-effect) or chronically impaired.
  • It is common for older adults to have at least mild decreases in kidney function.
  • Many medications must be dosed differently, if a person has decreased kidney function.
  • Laboratories now routinely use the patient’s age and creatinine level to calculate an “estimated glomerular filtration rate,” which represents the filtering power of the kidneys. This is considered a better measure of kidney function than simply relying on creatinine and BUN levels.
• Glucose levels represent the amount of sugar in the blood.
  • If they are higher than normal, this could be due to undiagnosed diabetes or inadequately controlled diabetes.
  • If the glucose levels are on the low side, this is called hypoglycemia. It is often caused by diabetes medications, and may indicate a need to reduce the dosage of these drugs.

For more details on these tests, see Medline: Basic Metabolic Panel. From this page, you can find links to additional pages which explain each of the above electrolytes and metabolic components in detail, including common causes of the result being abnormally high or low.

3. Comprehensive metabolic panel 

What it measures: This panel includes the items above in the basic metabolic panel, and then usually includes an additional seven items. For this reason, it’s sometimes referred to as a “chem-14” panel. Beyond the seven tests included the basic panel (see above), the comprehensive panel also adds:

• Calcium
• Total protein
• Albumin
• Bilirubin (total)
• Alkaline phosphatase
• AST (aspartate aminotransferase)
• ALT (alanine aminotransferase)

What the comprehensive metabolic panel is often used for:

• Calcium levels are usually regulated by the kidneys and by certain hormones.
  • Blood calcium levels are not usually a good way to assess calcium intake or total calcium stores in the bones and body.
  • High or low blood calcium levels can cause symptoms, including cognitive dysfunction, and usually indicate an underlying health problem. They can also be caused by certain types of medication.
• Albumin is one of the key proteins in the bloodstream. It is synthesized by the liver.
  • Low albumin levels may indicate a problem with the liver or a problem maintaining albumin in the bloodstream.
  • Malnutrition may cause low albumin levels.
• AST and ALT are enzymes contained in liver cells.
  • An elevation in these enzymes often indicates a problem affecting the liver. This can be caused by medications or by a variety of other health conditions.
• Bilirubin is produced by the liver, and usually drains down the bile ducts and into the small intestine. Some bilirubin is also related to the breakdown of red blood cells.
  • An increase in bilirubin can be caused by gallstones or another issue blocking the bile ducts.
• Alkaline phosphatase is found throughout the body, but especially in bile ducts and also in bone.
  • Higher levels are often caused by either a blockage in the liver or by a problem affecting bone metabolism.

For more details on these tests, and the possible causes of abnormal results, see Medline: Comprehensive Metabolic Panel.

4. Lipid (cholesterol) panel

What it measures: These tests measure the different types of cholesterol and related fats in the bloodstream. The panel usually includes:

• Total cholesterol
• High-density lipoprotein (HDL) cholesterol, sometimes known as “good” cholesterol
• Triglycerides
• Low-density lipoprotein (LDL) cholesterol, sometimes known as “bad” cholesterol
  • LDL results are usually calculated, based on the other three results

People are often asked to fast before having their cholesterol checked. This is because triglycerides can increase after eating, and this can cause a falsely low LDL to be calculated. However, experts have recently concluded that in most cases, it’s not necessary for people to fast; it’s inconvenient and only makes a small difference in test results.

What the lipid panel is often used for:

• These tests are usually used to evaluate cardiovascular risk in older adults.
• Higher than normal total or LDL cholesterol levels are sometimes treated with a medication, such as a statin. They can also be reduced by dietary changes (see Your Guide to Lowering Cholesterol with Therapeutic Lifestyle Changes, from the NIH).
• For more on these tests, see Medline:  Cholesterol testing and results.

6 more blood tests that I order often

Here are six other types of tests that I often order on my older patients:

1. Tests related to thyroid function

What these measure: These tests can be used to screen for thyroid disorders, or to help calibrate the dosage of thyroid replacement medications.  The most commonly used tests are:

• Thyroid stimulating hormone (TSH)
• Free thyroxine (“free T4” or FT4)

In more complicated situations, other tests related to thyroid function may also be ordered.

What these tests are often used for:

• Thyroid problems are common in older adults (especially older women), and are associated with symptoms such as fatigue and cognitive difficulties.
• If an older person is having symptoms that could be related to a thyroid problem, the first step is to check the TSH level.
• TSH usually reflects the body’s determination of whether the available thyroid hormone is sufficient or not.
  • If the thyroid gland is not making enough thyroid hormone, TSH should be higher than normal.
• Free T4 is often used to confirm a thyroid hormone problem, if the TSH is abnormal.

For more information about thyroid problems in older adults, see HealthinAging.org: Thyroid Problems. You can also read a more in-depth scholarly article here: Approach to and Treatment of Thyroid Disorders in the Elderly.

2.  Tests related to vitamin B12 levels

What these measure: These measure the serum levels of vitamin B12 and provide information as to whether the level is adequate for the body’s needs.  The two tests involved are:

• Vitamin B12
• Methylmalonic acid

Depending on the situation, if an older adult is found to have low vitamin B12 levels, additional testing may be pursued, to determine the underlying cause of this vitamin deficiency.

What these tests are often used for:

• Vitamin B12 deficiency is quite common in older adults, and can be related to common problems such as fatigue, memory problems, and walking difficulties.
• Methylmalonic acid levels in the body are related to vitamin B12 levels, and can help confirm a vitamin B12 deficiency.
  • It is especially important to check this, if an older person has vitamin B12 levels that are on the low side of normal.
  • Low vitamin B12 levels are associated with higher-than-normal methylmalonic acid levels
• For more information, see: How to Avoid Harm from Vitamin B12 Deficiency.

3. Glycated hemoglobin (Hemoglobin A1C)

What it measures: Glycated hemoglobin is formed in the body when blood glucose (blood sugar) attaches to the hemoglobin in red blood cells.  It is normal for glucose to do this, but if you have more glucose in the blood than normal, your percentage of glycated hemoglobin will be higher than normal. The higher one’s average blood sugar level, the greater percentage of glycated hemoglobin one will have. A result of 6.5% or above is suggestive of diabetes. For more information:

• Hemoglobin A1C test

What this test is usually used for:

• This test is most often ordered to monitor the blood sugar control of people with diabetes.
  • Whereas a blood glucose level (which can be checked by fingerstick or as part of a basic metabolic panel) reports the blood glucose level at a specific moment in time, a hemoglobin A1C reflects how high a person’s blood sugar has been, on average, over the prior three months.
• A hemoglobin A1C test can also be used as part of an evaluation for possible diabetes or pre-diabetes.
• Older adults should work with their doctors to determine what A1C goal is right for them. It is often appropriate to aim for a slightly higher goal in older adults than in younger adults. For more on this, see HealthinAging.org: Diabetes Care & Treatment.

4. Prothrombin time (PT) and International Normalized Ratio (INR)

What it measures: These two tests are used as a measure of how quickly a person’s blood clots. People taking the blood-thinner warfarin (brand name Coumadin) must have this regularly monitored. For more information:

• Prothrombin time (PT)

What this test is usually used for:

• The INR is calculated by the laboratory, based on the prothrombin time. In people taking warfarin, the usual goal is for the INR to be between 2.0 and 3.0.
  • The most common reason older adults take warfarin is to prevent strokes related to atrial fibrillation.
  • Warfarin may also be prescribed after a person has experienced a blood clot in the legs, lungs, or elsewhere.
• The prothrombin time is also sometimes checked if there are concerns about unexplained bleeding, severe infection, or the ability of the liver to synthesize clotting factors.

5. Brain natriuretic peptide (BNP) test

What it measures: Despite the name, BNP levels are mainly checked because they relate to heart function (not brain function!). BNP levels go up when a person’s heart cannot pump blood as effectively as it should, a problem known as “heart failure.” For more information on this test:

• Brain natriuretic peptide (BNP) test

A related, but less commonly used, test is the “N-terminal pro-B-type natriuretic peptide” (NT-proBNP) test.

What this test is used for:

• Checking a BNP level is mainly used to evaluate for new or worsening heart failure. This is a common chronic condition among older adults, which can occasionally get worse.
• The BNP test can be especially useful in evaluating a person who is complaining of shortness of breath.
  • Shortness of breath can be caused by several different problems, including pneumonia, chronic obstructive pulmonary disease, pulmonary edema, angina, and much more.
  • A low BNP level means that at that moment, the shortness of breath is unlikely to be due to heart failure.
• Checking BNP levels over time is also sometimes used to monitor a person’s heart failure and response to treatment.
• For more about heart failure, see MayoClinic.org: Heart failure tests and diagnosis and also HealthinAging.org: Heart failure.

6. Ferritin

What it measures: The body’s serum ferritin level is related to iron stores in the body. For more about this test:

• Ferritin

Depending on the situation, if an older person’s iron levels need further evaluation, additional tests can be ordered.

What this test is used for:

• Ferritin levels are most commonly used as part of an evaluation for anemia (low red blood cell count). A low ferritin level is suggestive of iron-deficiency, which is a common cause of anemia.
  • Studies estimate that only a third of anemias in older adults are due to deficiencies in iron or other essential elements.
  • It’s important to confirm iron deficiency by checking ferritin or other tests, before relying on iron to treat an older person’s anemia.
• Ferritin levels are also influenced by inflammation, which tends to make ferritin levels rise.
• If the ferritin levels are borderline, or if there are other reasons to be concerned about an older person’s ability to manage iron, additional blood tests related to iron may be ordered.
• For more on evaluating and treating anemia in older adults, see Anemia in the Older Adult: 10 Common Causes & What to Ask.

Obviously, there are many more tests that can be ordered as part of the medical care of older adults. But the tests I cover above are, by far, the ones I order the most often.

Tips to help you benefit from your blood tests and results

Here are my top tips:

1. Be sure you understand why a given test is being ordered. Is it meant to help evaluate a symptom? Monitor a chronic condition? Assess whether a treatment is working?

You will understand your own health issues better, if you ask questions about the purpose of the blood tests your doctors are proposing.

In general, blood tests should only be ordered for a reason, such as to evaluate a concerning symptom, to monitor a chronic disease, or to check for certain types of medication side-effect.

Keep in mind that it’s only occasionally appropriate to order blood tests for “screening.” A screening test means a person doesn’t have any symptoms. Such screening blood tests are only recommended for a handful of conditions.

For more on preventive health care and screening tests that may be appropriate for older adults, see 26 Recommended Preventive Health Services for Older Adults.

2. Ask your doctor to review the results and explain what they mean for your health. Try to look at the report with your doctor. It’s especially important to ask about any result that is flagged as abnormal by the laboratory system.

For instance, I have found that many older adults are unaware of the fact that they have mild or moderate kidney dysfunction, even though this has been evident in prior laboratory tests. This happens when people do not review reports and ask enough questions.

Wondering why the doctor wouldn’t tell an older person that the kidney function is abnormal?

Well, if it’s been going on for a while, the doctor might think the older person already knows about this issue. Or perhaps the doctor mentioned it before, but the older person didn’t quite hear it. It’s also not uncommon for doctors to just not get around to mentioning a mild abnormality that is pretty common in older people, such as mild anemia or mild kidney dysfunction.

3. Ask your doctor to explain how your results compare with your prior results. Laboratory reports will always provide a “normal” reference range. But what’s usually more useful is to see how a given result compares to your previous results.

For instance, if an older person’s complete blood count (CBC) shows signs of anemia, it’s very important to look at prior CBC results. This helps us determine what the “trajectory” of the blood count is. A blood count that is drifting down — or worse yet, dropping fairly suddenly — is much more concerning than one that has been lower-than-normal, but stable for the past year. Ditto test results suggesting diminished kidney function, and for many other abnormal blood test results.

Of course, you’ll want to understand what might be the cause of an abnormal result regardless of the trajectory. But a worsening blood test result usually means the issue is more urgent to sort out.

4. Request copies of your results, and keep them in your own record system. Past laboratory results provide incredibly useful information to health providers, and can be very useful to you as well.

If you keep your own copies of results, you’ll be better able to:

• Share them with new doctors, if you change health providers, move to a new city, or have to go to the emergency room.
• Research your health condition, in order to better understand it and know what questions to ask your doctor.

For instance, one of my family members recently had a “routine” cholesterol panel done. He takes no medications, is quite fit, and is in good health, so he was surprised when some of his results came back higher than normal. We promptly reviewed his previous results, from three years ago, and found that those results were within normal range. So this family member is now in the process of reconsidering his diet.

If he hadn’t had copies of his previous labs, he could have asked his doctor. But it’s much faster and more convenient to be able to look in your own records!

And don’t just rely on looking up past results through a patient portal. Clinics will often remove your access, if you are deemed to have left the practice.  So it is very important to keep your own copies of results.

For more on the benefits of maintaining your own personal health record — or a health record for an older parent — see How to Use a Personal Health Record to Improve an Older Person’s Healthcare.