Normal Reference Values for Vital Signs and Laboratory Parameters
The normal reference values for vital signs and laboratory parameters should be based on population-specific data that accounts for age, sex, ethnicity, and other relevant factors, as these significantly impact the interpretation of clinical measurements.
Vital Signs Reference Values
Blood Pressure
- Normal BP: <120/80 mmHg 1
- Elevated BP: 120-129/<80 mmHg 2
- Stage 1 Hypertension: 130-139/80-89 mmHg 2
- Stage 2 Hypertension: ≥140/90 mmHg 2
Blood pressure values should be interpreted with consideration of demographic factors:
- BP tends to be higher in older adults 2
- Women may have lower normal thresholds than men 2
- Ethnic variations exist, with different reference ranges needed for different populations 2
Heart Rate
Respiratory Rate
- Normal range: 10-29 breaths per minute for adults 2
- Abnormal: <10 or >29 breaths per minute 2
- For infants <1 year: <20 breaths per minute is abnormal 2
Oxygen Saturation
- Normal: ≥94% 1
- Mild hypoxemia: 90-94% (PaO₂ 60-80 mmHg) 1
- Moderate hypoxemia: 80-90% (PaO₂ 45-60 mmHg) 1
- Severe hypoxemia: <80% (PaO₂ <45 mmHg) 1
- Profound hypoxemia: <56% (PaO₂ <30 mmHg) 1
Temperature
- Standard normal body temperature is approximately 37°C (98.6°F)
- For accurate oral temperature measurement, the thermometer should remain in the mouth for 6-7 minutes 3
Laboratory Parameters Reference Values
Hematology
Hemoglobin (Hb)
Men: Normal range varies by kidney function:
- eGFR >80 mL/min/1.73m²: Reference value
- eGFR 70-80 mL/min/1.73m²: 0.1 g/dL lower
- eGFR 60-70 mL/min/1.73m²: 0.1 g/dL lower
- eGFR 50-60 mL/min/1.73m²: 0.2 g/dL lower
- eGFR 40-50 mL/min/1.73m²: 0.8 g/dL lower
- eGFR 30-40 mL/min/1.73m²: 1.4 g/dL lower
- eGFR 20-30 mL/min/1.73m²: 3.9 g/dL lower
- eGFR <20 mL/min/1.73m²: 1.9 g/dL lower 2
Women: Similar pattern of decline with decreasing kidney function 2
Anemia definition: <13.0 g/dL in males and <12.0 g/dL in females 2
Hematocrit (Hct)
- Follows similar patterns to hemoglobin, decreasing with declining kidney function 2
Cardiac Function Parameters
- Left Ventricular Ejection Fraction:
Blood Glucose
- For critically ill patients, blood glucose measurements should account for:
- Sampling site (arterial, venous, capillary)
- Technology used for measurement
- Patient factors like hematocrit 2
Important Considerations
Population-specific reference ranges: Reference values should be obtained from studies of "normal" or "healthy" subjects with the same anthropometric characteristics (sex, age, height) and ethnic background as the patient being tested 2.
Measurement technique matters: For example, blood pressure should be measured on the upper arm while the arm is resting at approximate heart level 3.
Technology and sampling considerations: The accuracy of measurements depends on the technology used and sampling method. For example, capillary blood sampling in hemodynamically unstable patients can introduce significant errors 2.
Clinical context: Normal ranges may differ in specific populations. For instance, COPD patients may tolerate lower oxygen saturation levels (as low as 80%) 1.
Outcome-based reference values: The most logical way to define health-related reference ranges is by relating diagnostic measurements to clinical outcomes rather than just statistical distributions 2.
Temporal considerations: For some measurements, the timing and frequency of assessment are important factors in interpretation 2.
By understanding these reference values and their context-specific variations, clinicians can more accurately interpret vital signs and laboratory parameters to guide clinical decision-making.