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A Pretty Thorough Guide to Reading Lab Results

Kevin Whipple

If, like most of us, you receive medical information from your doctor’s office through a patient portal, you’re probably familiar with the slight panic that sets in when you receive a message letting you know your lab results are ready. 

Lab results often feature dizzying lists of percentages, ratios and mysterious abbreviations. One thing you probably won’t find are clear explanations of what it all means. If anything’s amiss, your doctor should reach out and talk you through the concerning findings. But even if everything looks OK, it’s still useful to know how to decipher your results. Here’s a breakdown of common lab tests and what they tell you.

Understanding lab test basics

In the past, average, healthy patients might have received lab tests about once a year. But in recent years, the US Preventive Services Task Force, which makes evidence-based recommendations for preventive care, has adjusted its guidelines for routine blood and urine screening. Now, you’re more likely to get lab tests done less frequently, and they’ll be tailored to your symptoms, age and family medical history.

“A long time ago, people would come in for a physical and they would get a urine test, a cholesterol test — even if they were 30 years old,” says Elizabeth Cory, a nurse practitioner at Valley Medical Group in Easthampton, Massachusetts. “But all of that, when it was studied, turned out not to be beneficial in decreasing mortality.” 

Some providers do still conduct routine screenings in order to obtain baseline information about their patients’ health. Essentially, this helps them understand what’s normal for your body. A standard lab panel measures blood count and cholesterol, and checks for anemia and potential thyroid issues, says Dr. Carl Beauzile, a physician at Chicopee Health Center in Massachusetts. 

Doctors might order specific lab tests more often for patients at a high risk of developing life-threatening diseases and others who are currently living with certain conditions. Obesity, diabetes, smoking, and family history of certain diseases, like cancer or anemia, are common reasons doctors might approach testing this way. 

Other lab tests become important as you get older: Cholesterol screening for healthy adults generally begins around age 40, while men need PSA tests (prostate cancer screenings) around 55, and women start getting regular thyroid testing, called TSH, in their 50s. 

How to know if your results are normal

It’s not your responsibility to interpret lab results or determine if they warrant follow-up care. Those tasks fall to your doctor. But lab results are a source of insight into your health, and knowing how to read them can be both useful and empowering. Most lab results posted to a patient portal include both absolute values and reference ranges. A reference range gives you a high value and low value — anything between them is typically considered normal.

If a result is outside the reference range, don’t panic. Results that fall slightly out of range are very common and occur for many reasons, and they don’t necessarily require intervention. “There’s no one-size-fits-all with lab tests; it’s very individualized,” Beauzile explains.

Cory adds, “Things can be a little bit off in any of the labs, but it really has to be a pattern for us to be concerned. It all depends on how much it’s out of range, and why we did the test in the first place.” 

The reference range will be expressed in the same format as the corresponding result, which varies by test. It’s usually listed as a ratio (e.g., 32-36 milligrams per deciliter, or mg/dL, of blood.) 

Common lab test results and how to understand them

 The most common lab tests require submitting a blood or urine sample. Basic blood and urine tests screen for common medical conditions, such as high cholesterol, pre-diabetes and thyroid disorders. Providers can also order more complex panels from these samples.

Here’s a breakdown of what’s usually included in common lab tests. (This list isn’t exhaustive, so talk to your doctor if you have questions about specific tests.)

Urine tests

Urine tests (also called urinalysis) have been a useful diagnostic tool for millennia. Doctors might order urine tests to screen for prediabetes or diabetes, measure liver and kidney function, and/or check for sexually transmitted infections (STIs) or other non-sexual infections. Basic information about your urine, like its color and smell, also provide useful insights into your body’s health.

  • When you review your urine test results, you’ll likely see measures of the acidity (pH) of your urine, and its gravity, which assesses its density compared to the density of water. You’ll also see an assessment of its clarity (is it clear or cloudy?) and color. This basic information helps your provider gauge your hydration levels and assess your kidney and liver health. 
  • The amount of glucose and ketones in your urine are both connected to the overall sugar levels throughout your body; high or low sugar levels can be a sign that something’s off. Along with other factors, doctors look at your sugar levels when screening for diabetes.
  • Bilirubin is a component in bile, a substance produced by the liver. High levels of bilirubin in the urine — or its by-product, urobilinogen — can indicate a liver issue.
  • The amount of protein in your urine is used to evaluate your kidney function. Trace amounts of protein are normal, but too much can be a sign the kidneys aren’t working properly.
  • The amount of leukocytes and/or nitrites in your blood can indicate a bacterial infection. For instance, a urinary tract infection is a common cause of an uptick of leukocytes in the urine. 

Further, microscopic analysis of urine checks for trace amounts of other substances, such as:

  • Blood, which can be a sign of kidney disease and other serious conditions. 
  • Bacteria, which can be a sign of a bacterial infection. 
  • Amorphous crystals, which form in the urine and can become kidney stones.
  • Epithelial cells, which are cells on bodily surfaces that can slough off and end up in your urine. High numbers can indicate you might have a urinary tract infection or liver disease. 

Having small amounts of these substances is normal — your results might say “occasional” or “few,” instead of a number — but if your provider is concerned, they might order further testing.

Blood tests 

Your blood is a rich source of health data. Doctors use blood tests to identify signs of conditions including anemia, iron deficiency, heart disease, high cholesterol and autoimmune or bone marrow disorders. Blood tests can also provide insight into major organs, including the kidneys, liver and lungs, and how well they’re functioning.

If your doctor orders basic blood tests to gauge your overall state of health, here are some of the results you might see: 

A complete blood count (CBC) is a panel that measures the concentration of cells that make up your blood.

  • RBC is the number of red blood cells, which carry oxygen from the lungs. Healthy blood contains many more red blood cells than white ones.
  • WBC is the number of white blood cells, which fight infection. (Your doctor might also order a CBC differential panel, which shows the makeup of different types of white blood cells.)
  • Platelets (Plt), also called thrombocytes, are cell fragments that help prevent clotting. This value is presented as the number (in thousands) of platelets per microliter of blood. 
  • Hemoglobin (Hgb or Hb) is a protein molecule that helps red blood cells carry oxygen; the amount of hemoglobin in your blood indicates how well your body is transporting oxygen.
  • Hematocrit (Hct or Ht) is the percentage of your blood that’s composed of red blood cells.

A lipid panel analyzes the amount of cholesterol and other types of fats in your blood, collectively called lipids. High levels of certain types of cholesterol can cause heart disease. High cholesterol is also linked to conditions including diabetes, alcoholism and hypothyroidism. A standard panel measures:

  • Total cholesterol, the sum of all the cholesterol found in your blood
  • Low-density lipoprotein (LDL), your “bad cholesterol”
  • High-density lipoprotein (HDL), your “good cholesterol”
  • Triglycerides, a type of fat found in blood, derived mainly from food 

Your results will be expressed in milligrams of cholesterol per deciliter of blood (mg/dL). They might be presented on a chart showing normal, borderline high and high values, for context.

A basic metabolic panel (BMP), also called an electrolyte panel, measures eight different substances in your blood:

  • Urea nitrogen is a natural waste product. Measuring it can help assess kidney functioning.
  • Carbon dioxide (CO2) is a waste product created when you expend energy. Measuring it can help assess kidney and lung functioning.
  • Creatinine is a by-product of creatine, a compound broken down by muscles. Creatinine-dense blood can be a sign of kidney malfunction.
  • Glucose comes from the carbs we eat. Measuring blood glucose levels can help assess pancreatic functioning and screen for diabetes and hypoglycemia.
  • Chloride, which comes from salt, is an electrolyte that helps balance bodily fluids. Abnormal amounts can indicate digestive or intestinal issues.
  • Potassium is a mineral and an electrolyte; it’s important for nerve and muscle function. Abnormal amounts can indicate kidney disease.
  • Sodium is another mineral and electrolyte that’s found in food and important for nerve and muscle function. Low levels can indicate a condition called hyponatremia; high levels can indicate the  opposite problem, hypernatremia.
  • Calcium, a mineral consumed through food and supplements, strengthens bones and teeth. Low or high levels can be a sign of issues including bone and thyroid disease and kidney malfunction.

Should you fast before receiving a lab test?

Your provider should tell you whether or not to fast before a specific test. In general, fasting isn’t considered as critical as it once was. 

New research suggests eating normal-sized meals before blood tests doesn’t impact lab results, like levels of cholesterol and triglycerides, as much as previously thought. Other studies show that fasting before cholesterol tests has little effect on predicting future heart problems. And a 2020 study found no significant impact of black coffee on metabolic blood test results.

Not to mention, “people’s lives are moving faster now,” says Catherine Reed, a laboratory director at a Massachusetts hospital. “We’d much rather have them get their labs while they see their provider, sort of a one-stop-shop, rather than try to schedule that time back into their life on a day where they’ve fasted.”

Should you Google your lab results?

Advanced technology has made lab testing more efficient, but quick turnaround times mean that a patient might read their results before their provider has time to review them or add notes with useful context. 

“It’s okay to check the internet!” Beauzile says. “But we are here to clarify things, to reassure, and to take action.” 

If you’re concerned about a result, you can always send a message to your medical team. “Your provider is going to put your results in perspective with your whole medical history,” Reed adds. 

The next time your labs land in the patient portal, don’t freak out. Instead, use that time to understand what the results mean. The values tell you what’s going on in your body today, so you can care for it for years to come. 

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