Lab Analysis: Interpreting Results

Introduction to Lab Analysis

• This lecture series is about analyzing laboratory results, especially for hospitalized patients.
• Lab results offer objective data that enhances subjective information in patient assessment.
• A crucial skill for healthcare professionals is the ability to understand and use lab data.

Objective Data in Patient Assessment (SOAP Note)

• Objective data includes physical exam findings, signs and symptoms, and lab results like CBC and CMP.
• The series will explore how to interpret and act on lab findings methodically.
• A CBC includes white blood cell count, hemoglobin, hematocrit, platelet count, and mean corpuscular volume.
• Chem7 includes sodium, potassium, chloride, CO2 (bicarbonate), blood urea nitrogen, creatinine, and glucose.

Lab Analysis as Instruments

• Lab analysis is like using instruments to fly a plane, offering critical data.
• The clinical view is like looking out the window; in difficult cases (a storm), you need lab results.
• The instruments give a deeper insight into the patient's internal condition.
• Instruments must be interpreted given the patient's clinical presentation.

The Importance of Trending Lab Data

• Lab results reflect a single point in time.
• Observing trends in previous lab results is more informative than a single data point.
• Sodium levels within the normal range of 135-145 may indicate developing hypernatremia if on an upward trajectory.
• Proactive monitoring in critical, particularly in the ICU.
• Monitoring the rate at which lab values change is vital, like a pilot watching instruments.
• Clinicians determine the frequency and selection of lab orders, unlike the fixed instruments in a plane.
• Accurate diagnosis relies on ordering the correct tests like CT angio for pulmonary embolism, CBC for anemia, ABG for hypercapnia.

Lab Errors and Reliability

• Lab errors exist, with a significant error rate of about 0.45%.
• Most errors arise from sample drawing or mix-ups, not lab machines.
• One example is a potassium level that suddenly spikes and then normalizes, which suggests a likely lab error.
• Unlike pilots who are generally told to trust their instruments, clinicians should combine lab data with observations.
• If a lab result is clinically implausible, repeat the test to confirm before taking action.
• Drawing blood near an IV (e.g., central line with D5) can distort results, like falsely elevating glucose.
• If potassium is high, order an EKG to check for peaked T-waves, which would confirm hyperkalemia.

Key Takeaways

• Clinical impression should be supplemented by lab data, considering them in unison.
• Data trends are more valuable for demonstrating movement than single data points.
• Since lab results can be incorrect, trust but verify, and repeat if something seems wrong.
• Key considerations:
  • Which blood tests to order
  • How often the tests should be ordered
  • How low/high values must be to warrant automatic action