Laboratory Studies You Must Know

Lactate, D-Dimer, ammonia, CBC, coags, the BMP electrolytes one by one, kidney, liver, pancreas and cardiac markers — what each one means at the bedside.

Laboratory Studies You Must Know

*Please review your own organization's lab value ranges*

Lactate

Commonly used in the ER to help assess a patient's perfusion status. It's a byproduct of anaerobic metabolism, meaning the body isn't getting the blood flow or oxygen it needs, so it turns to anaerobic metabolism and lactate is a result of it. The higher the lactate the worse the patients perfusion status may be. A normal lactate is less than 2 mmol/L. The higher the worse off the patient may be, and typically from what I've seen, lactate levels above 5 indicate a very sick patient.

D-Dimer

When the body is breaking down a blood clot somewhere, D-Dimer is produced. The higher the D-Dimer, the higher chances a blood clot is actually present, and many providers will use a cut off of 500ng/ml when it comes to pulmonary embolisms. If the patient has a D-Dimer above 500, then a ct scan with contrast will most likely be ordered to rule out or in a PE.

Ammonia

A waste that is usually cleared by the liver and when there is a build up, it can result in patients presenting with altered mental status. Keep this in mind in patiens who have a history of liver failure and or chronic alcohol use. Normal is less than 80 mcg/dL.

CBC

• WBC: white blood cells fight infections, if you have a high amount, there is an infection somewhere in the body. Normal is 4.5-10. Neutrophils are mature wbc's while bands are the immature version. When a patient has a bad infection and they start having a higher number of bands, its called a Left shift, indicating that the body is unable to keep up with the infection and is even throwing immature wbc's at it. • Hemoglobin: in the ER, commonly used to evaluate if a patient will need a blood transfusion. The typical threshold is that a hgb less than 7 g/dL will get a blood transfusion. Of course, this is a rule of thumb. If your patient is actively bleeding, their hemoglobin may not be low when the labs result because the body hasn't had time to adjust and redistribute accordingly. • Platelets: clotting. If very low, less than 50, spontaneous bleeding can occur.

Coags

• Pt, INR, Ptt: the body's overall clotting ability. Useful when patients are on blood thinners. Checked when patients are having any sort of bleed like a GI and intracranial bleed to ensure they don't need to be reversed.

Thromboelastography (Teg)

Body clotting ability but shown with specific clotting factors. Used in patients with severe bleeding to help decide if the patient needs more PRBC's, plasma, platelets or even cryo. It helps guide therapy.

BMP: Electrolytes

Sodium

Normal is 135-145 mEq/L. • Hypernatremia: commonly as a result of Dehydration (Sepsis, DKA, working outside on a hot day and not drinking water) • Hyponatremia: Very critical when under 120. Water gets pulled into brain tissue and can cause seizures and other neuro symptoms, with seizures being the most important. A common cause is volume overload, others include cancers, medications, renal/liver failure. o Below 120s is critical r/t potential for seizures and other symptoms: key issue is to replace sodium slowly because if its done too fast a condition called osmotic demyelination syndrome can occur which essentially results in severe neuro symptoms. When the patient is actively seizing as a result of hyponatremia, the providers will be more aggressive in replacing sodium, once seizure stop, the replacement is done slowly. o If mild hyponatremia, the providers may order normal saline (sodium of 156) to replenish, if more severe, they may order 3% hypertonic saline. In emergencies, amps of sodium bicarbonate may be administered as it has sodium and most importantly readily available. o Nursing: Frequent neuro checks, monitor electrolytes, watch our for seizures, replace sodium slowly (yes the docs are putting in the orders, but you're giving it, so ensure you're doing it right.)

Potassium

Normal is 3.5-5 mEq/L. • Hyperkalemia: Critical when levels are above 6 and or with ECG changes (peaked T waves, widening QRS, Sine wave in cardiac arrest). Commonly as a result of muscle breakdown and kidney injury/failure. Hyperkalemia is very toxic and irritating to heart muscle, so a level above 6 specially when combined with ecg changes needs to be treated asap. Other signs besides the ECG are weakness and numbness/tingling. HyperK medications include calcium, insulin/dextrose, bicarb, lasix, albuterol, kayexalate and if needed dialysis. • Hypokalemia: Commonly as a result of gastrointestinal and absorption disorders, think poor oral intake, diarrhea and vomiting. Also irritating to the heart and needed by muscles to function, so levels below 3.5, but specially below 3, need to be replaced. Symptoms include weakness, numbness/tingling, muscle cramps and of course deadly heart rhythms. To replace, providers may order PO doses or IV. If PO, large pills, can irritate the stomach, but safer otherwise. If IV, must be on cardiac monitor, on a pump, no more than 10mEQ per hour on peripheral IV. If central line, most facilities allow up to 20mEq per hour.

Calcium

Normal 8.5-10.5 mg/dL. • Severe hypocalcemia can cause arrhythmias (QT prolongation), seizures and airway issues. Symptoms include tingling and cramps. Providers may order IV calcium such as calcium gluconate to replace. When patients receive large amounts of blood (think massive transfusion protocol), calcium may have to be replaced, as blood contains citrate, which binds calcium. If the total calcium level comes back low, providers may order an ionized calcium level, which is the active form of calcium. If ionized calcium level is low, this warrants prompt management. Calcium is very important to monitor in critical patients, remember that it also helps the heart contract, also causes hypotension when low and it stabilizes a lot of things. • Important for cardiac conduction, so keep in mind when patients present with bradyarrhythmia's-arrhythmias. • Hypercalcemia can also cause arrhythmias (QT shortening) and weakness. A common cause is dehydration, others include cancers and medications. To manage, providers may start with IV fluids to address the dehydration.

Magnesium

Normal 1.7-2.3 mg/dL. • Important for cardiac conduction and conduction throughout body • Low magnesium: places patient at a higher risk for arrhythmias, think ventricular arrhythmias, especially Torsades. It can also cause weakness and seizures. To manage, providers may order IV magnesium sulfate. Also keep in mind that low magnesium levels will make it hard to appropriately replace potassium. When replacing have pt on cardiac monitor and close monitoring as it can cause hypotension, flushing and at times sedation. (Be mindful that providers may order magnesium even if the level is not low, think COPD/Asthma exacerbations) • High magnesium levels are more uncommon, but deadly. It can lead to arrhythmias, respiratory depression and cardiac arrest. Providers may order IV calcium gluconate, it stabilizes the heart. (Just as with high levels of potassium.)

CO2 on the Chemistry

Normal 22-24. • On the chemistry, Co2 represents bicarbonade, so its useful for knowing acid-base status (Remember: not the same as respiratory co2) • Low CO2: represents metabolic acidosis, too much acid present. Causes can include dka, sepsis, shock (anything that leads to high levels of metabolic acidosis). So it signifies poor perfusion and worsening of the patients illness. • Useful in determining if metabolic acidosis is present. • Anion gap: Sodium - Chloride + CO2 (BICARB) o Normal is between 10-12

Kidney

• Creatinine: used to assess kidney function. Greater than 1.5 kidney function is beginning to show compromise. Is the perfusion to the kidneys compromised? Is the kidney itself damaged? Or is something past the kidney causing issues such as stone blocking the kidney from emptying? • GFR: Helps assess kidney function, normal is greater than 90. Useful to gauge whether the patients kidneys can tolerate contrast for CT and whether they can clear certain medications. • BUN: helps assess kidney function and whether the patient is dehydrated, low perfusion causes BUN to rise, 10-21 is normal. Also rises with protein breakdown. • BUN/CREATININE Ratio o High BUN with mildly elevated creatinine, think dehydration. o High BUN and High Creatinine, think kidney injury and renal dysfunction.

Liver

• ALT/AST: used to assess for liver dysfunction, the higher the worst off the liver is. ALT is more Liver specific. Causes of liver injury that result in high levels include alcohol use, medication toxicity (like acetaminophen OD), hepatitis. • Liver and INR, Bilirubin and Albumin. A high INR can indicate the liver is struggling to produce clotting factors. Elevated bilirubin can indicate the liver is not clearing and processing waste appropriately. Low albumin means the liver isn't producing what it should appropriately.

Pancreas

• Lipase/Amylase: used to assess function of pancreas, lipase is more specific. Causes of pancreatic issues can include alcohol use and gallstones.

Heart

• Troponins: useful in determining if heart damage is occurring. Start to rise in the blood at approximately 2 hours from injury. Used to gauge severity of heart damage occurring. Important to trend troponin levels, often repeated at 3 hour or 6 hour mark by providers to evaluate for a rise in troponin which may indicate heart damage is occurring. Often paired with an ECG. Troponins can rise from STEMIs, NSTEMIs, Arrythmias, heart failure, Pes. (The list goes on.) • BNP: used to assess for heart failure. Normal bnp is 100 ng/L. A bnp above 500 is typically a sign of a heart failure exacerbation. In my patient population, I commonly see Bnp's in the thousands.

Urine

• Urine Tox Screen: looks for illicit drugs like amphetamines and opioids • Urinalysis: measures and looks for a variety of things inside the urine like wbcs, nitrate, ketones, bacteria, blood, myoglobin, specific gravity, etc • Urine Culture: looks for bacteria in the urine

Blood Cultures

Looks for bacteria in the blood and helps us figure out which abx would work best for the patient.

Updated 12 Sep 2026