AARP Smart Guide to Understanding Your Routine Lab Work

11. Non-HDL cholesterol

Your provider or lab calculates this metric using your other cholesterol numbers. It measures all the bad cholesterol particles, not just LDL, so it’s “a more comprehensive marker [of your risk] than simply LDL,” Shapiro says. The goal is less than 130 mg/dl. Some labs include a similar measure called a cholesterol ratio, which is your total cholesterol divided by your HDL. A lower ratio suggests a lower risk.

12. ApoB (Apolipoprotein B)

This measurement is not always part of a traditional lipid panel, but your doctor might order it to get a better read on your heart health. This blood test is similar to non-HDL in that it reveals the number of particles carrying bad cholesterol in your bloodstream, but it’s slightly more precise, Plutzky says.  The goal is 66-133 mg/dl for men and 60-117 mg/dL for women.

13. Lipoprotein(a)

Lipoprotein(a), or Lp(a), is another fatty particle that circulates in your bloodstream, and some models show it’s six or seven times more dangerous than LDL. Lp(a) is genetically inherited and is now recognized as a key reason why some healthy people without typical risk factors have heart attacks and strokes. Shapiro says he tests for it in every patient, adding that a growing number of providers are following suit and including it as part of a standard cholesterol screening. According to the American Heart Association, a reading of 50 mg/dL or higher increases your risk of cardiac conditions.

COMPREHENSIVE METABOLIC PANEL: THE BASICS

14. Types of metabolic panels

Doctors typically order one of two metabolic panels. A basic metabolic panel (BMP) is a routine blood test that measures eight factors, including electrolytes, glucose and kidney function markers. A comprehensive metabolic panel (CMP) includes those tests plus others that measure certain proteins and liver function. Both panels can help your health care provider detect health conditions, disorders and diseases.

15. Glucose (blood sugar)

This test measures your blood sugar after you’ve fasted for eight to 12 hours. A high result is often the first clue that your body isn’t making or using insulin the way it should, Koncilja says. The normal range is 70 to 99 mg/dL. A blood sugar level of 126 mg/dL or higher may indicate type 2 diabetes. If it’s between 100 and 125 mg/dL, that points to prediabetes, a warning sign that you’re on the path toward diabetes.

To confirm the diagnosis, your doctor will likely order another test called the A1C. The good news? Prediabetes is reversible, and knowing you have it is “like a big siren saying ‘get your health together,’ ”  Koncilja says. Eating a healthy diet, staying active, losing even a small amount of weight and getting enough sleep can help bring your blood sugar back into a healthy range. (AARP: 11 Simple Ways to Lower Your Blood Sugar)

16. Total calcium

Calcium is one of the most important minerals for good health, and this test measures the amount in your blood. The normal range is 8.8 to 10.4 mg/dL, though different labs may have different ranges. Too much calcium (hypercalcemia) can be a sign of kidney, bone or thyroid disorders, or certain cancers, Koncilja says. Low calcium (hypocalcemia) may indicate problems with your liver, kidney or pancreas, or could just indicate that you’re not getting enough calcium, vitamin D or magnesium in your diet. Some medications can also affect calcium levels. Because high or low calcium levels can be a sign of so many different conditions, if your levels are off it’s important to talk to your provider about next steps, says Koncilja. (Note: This test does not measure the amount of calcium in your bones.)

COMPREHENSIVE METABOLIC PANEL: KIDNEY FUNCTION TESTS

17. Blood urea nitrogen (BUN)

Urea nitrogen is a waste product that comes from the breakdown of proteins in the foods you eat, and this test measures the amount in your blood. While the “normal” BUN levels typically range from 5 to 20 mg/dL, they can vary with age, sex and health conditions. While they tend to increase as you get older, a high level can suggest kidney problems, says Koncilja, adding that your BUN level may be most helpful when looked at as a ratio with your creatinine level (below). If your BUN-to-creatinine ratio is over 20, that’s a sign of dehydration, Koncilja says: “It’s one of the most common things you see, because people don’t drink enough water.”  (AARP Smart Guide to Kidney Health)

18. Creatinine

Creatinine is a waste product your body makes when you use your muscles, says Suzanne Watnick, a nephrologist and professor of medicine at the University of Washington in Seattle. (Normal ranges are 0.5-1.1 mg/dL for women and 0.6-1.2 mg/dL for men.) Your kidneys usually filter it out, so high levels can indicate kidney problems. Low levels may point to liver issues. However, creatinine levels can be off in people who are fluid-depleted, take certain medications or have very high or very low muscle mass, Watnick says.

For instance, an 80-year-old, 90-pound woman without a lot of muscle mass might have a low creatinine level that looks normal on paper but could actually signal kidney disease for her. That’s why “you really need to meet with your primary care provider” to help interpret results, says Watnick. This is typically done in conjunction with a urinalysis, or your doctor may order a kidney function test called cystatin-C, which can offer a more accurate read.

19. Estimated glomerular filtration rate (eGFR)

Labs calculate your estimated GFR using your creatinine level, your age and other factors to give you a better snapshot of how well your kidneys are working compared to creatinine alone, says nephrologist John Friedewald, medical director of kidney and pancreas transplantation at Northwestern Memorial Hospital in Chicago. The normal range is above 90 mL/min for those younger than 60; above 85 for those between 60 and 69; and above 75 for those over 70. A low eGFR can signal kidney disease. It can also indicate that your medications need to be adjusted or that you simply need to drink more water, Friedewald says. As with creatinine, having very high or very low muscle mass can skew the results.

COMPREHENSIVE METABOLIC PANEL: LIVER FUNCTION TESTS

20. Bilirubin

A bilirubin test measures the levels of bilirubin in your blood. (The normal range is 0.3 to 1 mg/dL.) Bilirubin is a yellowish waste product that’s created when your body breaks down old red blood cells. Normally, the liver helps clear it out, Koncilja says, but if you have liver disease, a bile duct blockage like gallstones or a disease that destroys red blood cells, bilirubin can build up. If it gets too high, you can develop jaundice, a yellowing of the skin and eyes.  

21. Albumin

This protein is made in your liver. It transports important substances through your bloodstream and helps keep the right balance of fluids in your blood vessels. Typical ranges are 3.5 to 5 g/dL, though that can vary by lab. Low levels can signal liver or kidney disease, digestive diseases or malnutrition from a condition like cancer or anorexia, Koncilja says. High levels can be caused by dehydration and certain medicines such as steroids and insulin. Your provider should check your urine for albumin, too, Watnick says. If you have a serious kidney disease, your body will be wasting a lot of this protein in the urine, and your blood levels will be low.

22. Total protein

This test measures the total amount of protein in your blood, including albumin and a type of protein called globulin. It is often used to assess overall health and to investigate potential causes of symptoms such as swelling, fatigue or unexplained weight loss. The normal range is 6 to 8.3 g/dL. Low levels could indicate liver or kidney disease, malnutrition or a digestive condition like celiac disease or Crohn’s disease. High levels can be a marker of an infection or blood cancer.

23. Liver enzymes (ALT, AST and ALP)

These enzymes — ALT (alanine transaminase), AST (aspartate transaminase) and ALP (alkaline phosphatase) — are made in the liver. They’re often released into the blood if the liver is damaged or inflamed. Elevated levels may point to liver disease, but they can also signal other issues. For example, high ALP might suggest bone disorders, and elevated AST can result from muscle injury or systemic inflammation, Koncilja says. The ranges on these tests are most helpful when interpreted in conjunction with other lab results.

COMPREHENSIVE METABOLIC PANEL: ELECTROLYTE TESTS

24. Sodium

This is a measure of the sodium concentration in your blood. Like other electrolytes, sodium helps control fluid balance and keeps your blood pH at a healthy level. The normal range is 135 to 145 mmol/L (millimoles per liter). Your sodium level can be affected by how much salt you eat, and it’s closely linked to blood pressure. If your blood sodium levels are too high or too low, it may mean that you have a kidney problem, dehydration or another medical condition. To bring levels down, avoid high-sodium packaged and prepared foods, drink more water, and consider using salt substitutes.

25. Chloride

This is another electrolyte in the body. It comes from salt and, like sodium, helps regulate the body’s fluid balance. The normal range is 96-106 mmol/L. Elevated chloride can indicate dehydration, kidney disease or metabolic imbalances, while low levels can be a sign of heart failure, lung problems or Addison’s disease, a disorder in which the body stops making critical hormones.

26. Potassium

Potassium is an essential mineral, and it’s another electrolyte that helps your nerves and muscles, including the heart, function properly. (Normal ranges are 3.7-5.2 mmol/L.) Too much potassium in your blood can be harmful and is often a sign of kidney disease, Watnick says. High potassium can also be a sign of Addison’s disease, poorly controlled diabetes or another medical condition, while low potassium can signal dehydration, nutritional deficiencies or an adrenal gland disorder. Your potassium levels can also be affected by certain medications or, in rare cases, a diet that’s too high or too low in potassium.

27. CO2/Bicarbonate

This test measures carbon dioxide (CO2) in your blood, which tells doctors your bicarbonate level. Bicarbonate is important because it helps regulate the acidity of your blood. The normal range is 23 to 29 mmol/L. Abnormal levels may indicate lung or kidney problems or metabolic imbalances. Some medications can also affect this test. 

COMPLETE BLOOD COUNT

28. White blood cell count (WBC)

This test measures your white blood cells, a key component of your immune system that helps your body fight infections and disease, says Christian. The normal range is 4,500 to 11,000 cells per microliter (μL). A high count most often indicates an infection, but it can also point to inflammation or an allergy. A low count can indicate some types of cancer, HIV or an autoimmune disorder. One part of this test, called a differential, identifies levels of different types of white blood cells, which can signal specific diseases, disorders or infections. “That can then help the doctor figure out the next set of tests,” Christian says. 

29. Red blood cell count (RBC)

Your red blood cells carry oxygen throughout your body, and this test measures the number of these cells present in a unit of your blood. (The normal range is 4.6 to 6.2 million/μL in men and 4.2 to 5.4 million/μL in women.) A low count may be a sign of anemia, malnutrition, kidney problems or certain types of cancer, while a high count can signal dehydration, heart or lung disease or some cancers. Your doctor will use this test in conjunction with other red blood cell measurements to better understand your health, says Christian.

30. Hemoglobin

Hemoglobin is the protein in red blood cells that binds to oxygen and distributes it from your lungs to the rest of your body. The normal range is 13 to 18 g/dL in men and 12 to 16 g/dL in women. A low hemoglobin level most often signals anemia, a condition that affects about 10 to 15 percent of adults age 60-plus. If you’re anemic, “it’s very, very important” to have your iron levels checked, Christian says, because low iron can indicate blood loss. Sometimes the cause is clear, such as recent major surgery or visible bleeding. But if there’s no obvious cause, doctors often recommend screening to examine the gastrointestinal tract for ulcers, polyps or even colon cancer that could be causing hidden blood loss. If your iron level is normal, other conditions associated with low hemoglobin include a lack of certain nutrients, liver or kidney disease and some cancers. Medications can also push down your levels. Elevated hemoglobin may indicate lung disease, heart disease or other conditions.

31. Hematocrit

This test measures the percentage of red blood cells in your body by volume. The normal range is 40 percent to 54 percent for men and 36 percent to 48 percent for women, but those figures can vary. It’s another test that can help a health care provider diagnose anemia. In addition to anemia, a lower-than-normal number could mean kidney problems, a lack of certain nutrients or leukemia. High levels can indicate lung disease, heart problems or dehydration. (AARP: What Every Older Adult Should Know About Anemia)

32. Platelet count

Platelets are blood cells that help with clotting, rushing to the site of a cut or injury to stop the bleeding. They are important, and your body has a lot of extra ones as a safety net. “A platelet count of 100 is all you need for us to say it’s fine for you to go to neurosurgery,” Christian says. (The normal range is 150,000/μL to 400,000/μL.) However, she says it’s still important for your doctor to investigate the cause if your count is low.  A low level can be a sign of cancer, while high levels put you at greater risk for blood clots. 

33. Mean corpuscular volume (MCV)

This test measures the average size of your red blood cells. The normal range is 80-100 femtoliters (fL). If they’re too small or too large, it can be a sign of anemia, liver disease or other conditions. However, this test is mostly used to help your doctor better understand what’s going on with your red blood cells, says Christian. For example, if someone is anemic and their red blood cells are small, that suggests an iron deficiency, while large cells indicate a B12 deficiency. If your other blood count levels are normal, you probably don’t need to worry too much if your MCV is out of range, Christian says.

34. Mean corpuscular hemoglobin (MCH)

This measures the average amount of hemoglobin in each red blood cell. The normal range is 27 to 31 picograms (pg) per cell. As with MCV, low scores indicate anemia caused by iron deficiency, while high scores can indicate a B vitamin deficiency. 

35. Mean corpuscular hemoglobin concentration (MCHC)

This number tells you how concentrated the hemoglobin is in your red blood cells. (The normal range is 32 to 36 g/dL.) Low hemoglobin content usually correlates with a low MCHC, Christian says, and often suggests iron deficiency. High MCHC is rare and can indicate a few rare conditions. But again, Christian stresses that if your other tests are normal, abnormalities on this test aren’t usually concerning.  

OTHER TESTS

36. Thyroid panel

The thyroid, a small gland in the front of your neck, produces hormones that help regulate brain activity, breathing, heart rate, temperature, nervous system, weight, metabolism and more. The most basic thyroid test measures levels of thyroid-stimulating hormone (TSH). Normal levels are between .4 and 4.0 milli-international units per liter (mIU/L). If your levels are too high, that could indicate hyperthyroidism, or an overactive thyroid. If your levels are too low, it’s a sign of hypothyroidism, or an underactive thyroid. Left untreated, both conditions can lead to serious health problems.

37. PSA test

The PSA test is a screening for prostate cancer. It detects levels of a protein in the blood called prostate-specific antigen (PSA). Elevated levels can signal prostate cancer; however, you’ll need additional testing to confirm that. High PSA levels can also appear when you have an enlarged prostate or a urinary tract infection.

According to the M.D. Anderson Cancer Center, doctors typically label PSA levels as either "elevated" or "non-elevated," because the range of what’s considered normal varies by age. For men age 59 or younger, the reading should be at or below 2.5 ng/mL. For men age 60 or older, it should be at or below 4.0 ng/mL.