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Your Lab Results Decoded

Wonder what all those numbers mean? So did we

En español l How’s your bilirubin level? And your BUN/creatinine ratio? Unless you enjoy reading Dictionary of Medical Terms, your routine lab results can seem downright cryptic. To help you decipher them, we asked Mark S. Lachs, M.D., author of  Treat Me, Not My Age, and Marie  A. Bernard, M.D., deputy director of the National Institute on Aging, to explain what all those numbers really mean.

Just be aware: Abnormal test results are fairly common, especially among older adults. “Fifty-plus folks tend to take more medications,” says Lachs, “and that can throw off test results. For example, diuretics can alter sodium and potassium levels; heparin can decrease your platelet count.” (These are real abnormalities that may need further treatment.) Plus, many older adults have chronic conditions that require more frequent testing — and the more you’re tested, the greater the likelihood of error. Finally, normal ranges are based on population averages, so normal for you might be slightly out of that range and of no significance. For instance, if you have Gilbert’s syndrome, a common, mild liver condition, you’d show elevated bilirubin, which could otherwise signal a serious liver dysfunction. “If you have known abnormalities, be sure to remind your doctor each time you get tested,” says Lachs.  

It’s a good idea to schedule a doctor’s appointment after undergoing lab work. That way, you can discuss any unusual results face-to-face.

Comprehensive Metabolic Panel - Measures kidney and liver function, electrolyte levels

What it is
Sugar in the blood

Normal Results
70 - 99 mg/dl

What a low number may mean 
Hypoglycemia, liver disease, adrenal insufficiency, excess insulin

What a high number may mean 
Hyperglycemia, certain types of diabetes, prediabetes, pancreatitis, hyperthyroidism

What it is
An electrolyte, which keeps your body in balance

Normal results
136 - 144 mEq/L

What a low number may mean 
Use of diuretics, diarrhea, adrenal insufficiency

What a high number may mean 
Kidney dysfunction, dehydration, Cushing's syndrome

What it is
An electrolyte and mineral

Normal results
3.7 - 5.2 mEq/L

What a low number may mean
Use of diuretics or corticosteroids (such as prednisone or cortisone)

What a high number may mean
Acute or chronic kidney failure, Addison's disease, diabetes, dehydration

What it is
An electrolyte

Normal results
96 - 106 mmol/L

What a low number may mean 
Emphysema, chronic lung diseases

What a high number may mean 
Dehydration, Cushing's syndrome, kidney disease

What it is
Gaseous waste product from metabolism

Normal results
20 - 29 mmol/L

What a low number may mean 
Kidney disease, certain toxic exposures, severe infection

What a high number may mean 
Lung diseases, including COPD

What it is
A waste product formed in liver and carried to kidneys, filtered out of blood, excreted through urine.

Normal results
7 - 29 mg/dL

What a low number may mean 
Malnutrition

What a high number may mean 
Liver or kidney disease, heart failure

What it is
A chemical waste produced by muscle metabolism

Normal results
0.8 - 1.4 mg/dL

What a low number may mean 
Low muscle mass, malnutrition

What a high number may mean 
Chronic or temporary decrease in kidney function

Normal results
10:1 to 20:1

What a low number may mean 
Malnutrition

What a high number may mean 
Blood in bowels, kidney obstruction, dehydration

What it is
A mineral stored in the hard part of bones

Normal results
8.5 - 10.9 mg/dL

What a low number may mean 
Calcium, magnesium, or Vitamin D deficiency; malnutrition;pancreatitis; neurological disorders

What a high number may mean 
Kidney disease, hyperparathyroidism, cancer, excess vitamin D intake

What it is
Chains of amino acids essential for the growth and repair of cells

Normal results
6.3 - 7.9 g/dL

What a low number may mean 
Malnutrition, liver or kidney disease

What a high number may mean 
Liver or kidney disease, dehydration, multiple myeloma

What it is
Protein that keeps fluid from leaking out of blood vessels and that nourishestissues and transports nutrients through the body

Normal results
3.9 - 5.0 g/dL

What a low number may mean 
Liver or kidney disease, malnutrition

What a high number may mean 
Dehydration

What it is
A pigment in the bile, a digestive fluid produced by the liver

Normal results
0.2 - 1.9 mg/dL

What a low number may mean 
Generally not a concern

What a high number may mean
Liver disease, bile duct disorder or red cell destruction

What it is
Enzyme found in the liver and bones

Normal Results
44 - 147 IU/L

What a low number may mean 
Malnutrition

What a high number may mean 
Paget's disease or certain cancers that spread to bone, bile duct obstruction, liver cancer

What it is
Enzyme found mostly in the liver

Normal Results
8 - 37 IU/L

What a low number may mean 
Generally not a concern

What a high number may mean 
Certain toxins such as excess acetaminophen or alcohol, hepatitis 

What it is
Enzyme found in liver, muscle, and other tissues

Normal results
10 - 34 IU/L

What a low number may mean 
Generally not a concern

What a high number may mean 
Excess acetaminophen, hepatitis, muscle injury

Health Turn: Your Lab Results Decoded - Key
Complete Blood Count (CBC) - Measures essential components of the blood

What it is
White blood cells defend the body against infection

Normal results
4,500 - 10,000 cells/mcL

What a low number may mean 
Autoimmune illness, bone marrow failure, chemotherapy, viral
infections

What a high number may mean 
Infection, inflammation, cancer, leukemia, intense exercise, stress,
corticosteroids

What it is
Red blood cells pick up oxygen from the blood and deliver it to tissues
throughout the body

Normal results
Male: 4.7 - 6.1 Mill/mcL
Female: 4.2 - 5.4 Mill/mcL

What a low number may mean 
Iron, vitamin B12, or folate deficiency; bone marrow
damage

What a high number may mean 
Dehydration, renal problems, pulmonary or congenital heart disease

What it is
Oxyrgen-carrying pigment in red blood cells

Normal results
Male: 13.8 - 17.2 g/dL
Female: 12.1 - 15.1 g/dL

What a low number may mean 
Iron, vitamin B12, or folate deficiency; bone marrow damage

What a high number may mean 
Dehydration, renal problems, pulmonary or congenital heart disease

What it is
The percentage of red blood cells in the blood

Normal Results
Male: 40.7% - 50.3%
Female: 36.1% - 44.3%

What a low number may mean 
Iron, vitamin B12, or folate deficiency; bone marrow
damage

What a high number may mean 
Dehydration, renal problems, pulmonary or congenital heart disease

What it is
Average size of red blood cells

Normal results
80 - 95 fL

What a low number may mean 
Iron deficiency

What a high number may mean 
Vitamin B12 or folate deficiency

What it is
The amount of hemoglobin in red blood cells

Normal Results
27 - 31 pg

What a low number may mean 
Iron deficiency

What a high number may mean 
Vitamin B12 or folate deficiency

What it is
Measures number of platelets — colorless blood cells integral to clotting

Normal Results
150 - 400 Thous/mcL

What a low number may mean 
Viral infections, lupus, leukemia, chemotherapy, pernicious anemia (due to vitamin B12 deficiency)

What a high number may mean 
Leukemia, myeloproliferative disorders (which cause blood cells to grow abnormally in bone marrow), inflammatory conditions

Health Turn: Your Lab Results Decoded - Key

Total Cholesterol
<200 mg/dL

HDL
>40 mg/dL

LDL
<130 mg/dL

Triglycerides
<150 mg/dL

Blood test: how to decode lab results

Photo by Science Photo Library/Getty Images

Frequent testing increases the likelihood of error.

These factors can throw off results:

  • Running or any high-intensity exercise can cause slight dehydration and show up as kidney insufficiency.
  • A sunburn can elevate white blood cell count, which typically signals inflammation.
  • Got a sick spouse or child but feel fine yourself? A nonsymptomatic cold virus can raise or lower white blood cell count.
  • An improper blood draw can cause a potassium spike; eating too much licorice can make it drop.
  • A specimen that sits for too long before testing by the lab can skew blood sugar readings.

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Also of interest: How to get patients to ask — and doctors to listen.

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