By Laura Hays, MD, FACEP

Visiting the emergency department (ED) can be unnerving, so understanding as much of the process as possible may help to ease anxiety and uncertainty.

When you arrive at the emergency department (ED), an initial assessment is performed to evaluate your “chief complaint” or primary reason for the visit, as well as your vital signs.  After that, a team member will decide which, if any, specialized testing is indicated.  This often includes drawing your blood for specific lab tests. These tests provide crucial information about your health, guiding your medical team in making accurate diagnoses and decisions about your care. But, what do they mean?  Do all abnormal results equate with badness?

Heres an overview of some of the most common lab tests performed in the ED and what they help to reveal about your health.  Remember, it’s your health, they’re your lab results, so be sure to ask questions and advocate for yourself and your loved ones.

Complete Blood Count (CBC)

A CBC measures different components of your blood, including red blood cells (RBCs), white blood cells (WBCs), platelets, hemoglobin and hematocrit.

WBCs help to fight infection but are often also elevated in times of acute stress and inflammation.  When a “differential” is performed on your CBC, it allows the WBCs to be broken down further into types of WBCs, with certain ones more specifically related to certain types of infection, cancers or bone marrow disorders.

Platelets help with blood clotting.  When you bleed, your body mobilizes platelets to start forming a clot in order to stop the bleeding process.  In the emergency department, we are mostly looking for abnormally LOW levels which may make you more prone to excessive or prolonged bleeding.

Related to RBCs, hemoglobin and hematocrit measure the oxygen-carrying capacity of your blood.  Abnormal levels can reveal anemia, other blood disorders, or may be elevated in dehydration.

Basic Metabolic Panel (BMP)

The BMP tests for several key electrolytes while also assessing overall kidney function and glucose metabolism.

Specific electrolytes included in a BMP include sodium, potassium, chloride and bicarbonate.  These electrolytes are important for all cellular functions and fluid regulation.  Abnormalities in any of these be affected by a number of medications, or may be indicative of or lead to acute illness or chronic conditions.  Imbalances in either direction (high or low) depending on the electrolyte can lead to various health issues, from dehydration, weakness and fatigue, to heart problems.

Also included in a BMP are blood urea nitrogen (BUN) and creatinine levels.  These represent kidney function and may fluctuate slightly based on hydration status.  However significant changes or abnormal elevation may indicate more serious kidney disease or insult.

The other component of a BMP is glucose which measures the blood sugar level at that point in time.  This is a more nuanced test.  Glucose levels that are very high or very low are concerning for diabetes or hypoglycemia.  However, keep in mind that most people coming to the emergency department are not fasting, may have just eaten a big meal or are acutely ill.  In these circumstances, blood glucose levels may be slightly higher than normal as your body naturally responds to food or stress, but not necessarily worrisome.

Comprehensive Metabolic Panel (CMP)

A CMP includes all the tests in a BMP, plus a few more that assess for liver function and protein.

Liver Enzymes include ALT, AST, alkaline phosphatase and bilirubin.  Elevated levels can indicate liver damage, liver disease or bile duct issues.  Also included in the CMP are total protein and albumin levels which are generally a marker of nutritional status.

Troponin (Tn)

If you experience chest pain, shortness of breath or other symptoms that suggest heart damage or heart attack, the primary cardiac enzyme – troponin – will be measured. Since the heart is a muscle, when it is stressed or damaged, it releases enzymes into the blood stream which can be measured at various intervals.  Troponin is the most specific and sensitive marker for heart damage and continues to rise over time.  Therefore, most protocols involve serial troponin testing, often upon arrival, then again at 1 and 3 hour intervals.  Certain conditions such as acute or chronic kidney failure can cause falsely elevated troponin levels.  For this and other reasons, the actual number is less important than the change (or “delta”) in subsequent measurements.  There may be a good reason they kept sticking you for blood!


A D-dimer test is often used when a blood clot is suspected, such as in cases of deep vein thrombosis (DVT) or pulmonary embolism (PE).  However, it is a relatively nonspecific inflammatory marker and may be elevated in other conditions.  It is used in “low risk” patients and is reassuring if negative.  Positive or elevated d-dimer levels do not necessarily indicate blood clot, but do prompt further workup usually in the form of imaging.  Keep in mind that there are adjustments made for age and pregnancy status and will be discussed by your doctor.

Arterial Blood Gas (ABG)

ABG tests measure the levels of oxygen and carbon dioxide in your blood, along with the blood’s pH. This test is vital for evaluating respiratory function and identifying conditions like respiratory failure, diabetic ketoacidosis (DKA) or other potential life-threatening conditions.

Urinalysis (UA)

A urinalysis can be used to assess for infections along the urinary tract.  If you are experiencing symptoms of a urinary tract infection (UTI), such as burning, discomfort, urgency, frequency, fevers or flank pain, it’s important that a UA is obtained using a “clean catch” technique.  Contaminated samples may skew results, hindering appropriate treatment plans.

The UA can also provide insight into potential kidney disease or kidney stones by assessing for blood or protein in the urine, as well as diabetes and hydration status through urine glucose and ketone levels.

Blood Cultures

When a serious bacterial infection is suspected, blood cultures are often obtained to look for bacteria in the blood stream, also known as bacteremia.  One caveat to blood cultures is that they generally take about 48 to 72 hours to result, which may influence your overall treatment course days later.

Ok, take a breath.  That may seem like information overload.  But, knowledge is power when it comes to your health.  These common lab tests provide essential information that helps emergency physicians make timely and accurate decisions, ensuring you receive the best possible care during your visit to the ED.

Understanding what these tests are and what they measure can help demystify the process and make your experience in the emergency department less stressful.

Dr. Laura Hays is an emergency physician with MEMA and co-founder of Lasting Impact Wellness Group – a health & well-being coaching and consulting company.  Check out her website at and tune in to her podcast “Lasting Impact Wellness” for more valuable insight and tips for optimal well-being.