From the Guidelines
C-reactive protein (CRP) is not typically measured as a percentage of total lymphocyte count (TLC), and instead, CRP is measured in mg/L or mg/dL, while TLC is a count of lymphocytes, measured in cells per microliter. These are separate laboratory values that aren't expressed as a ratio to each other in normal clinical practice.
Key Points
- CRP normal values are generally less than 10 mg/L or 1.0 mg/dL, though this can vary slightly between laboratories 1.
- TLC normal ranges are typically 1,000-4,800 cells/μL in adults.
- Both values are important in assessing inflammation and immune function, but they measure different aspects of the body's response to infection or inflammation.
- CRP rises rapidly in response to inflammation, while TLC may decrease during acute bacterial infections or increase during viral infections.
- These values should be interpreted separately within their own reference ranges rather than as a percentage relationship to each other.
Clinical Considerations
- The use of CRP and procalcitonin (PCT) can provide supportive and complementary information to clinical assessment in critically ill patients with a new fever and no clear focus of infection 1.
- Decisions on initiating, altering, or discontinuing antimicrobial therapy should not be made solely based on changes in PCT or CRP levels.
- Measuring PCT or CRP in critically ill patients with a low to intermediate clinical probability of bacterial infection is recommended in addition to bedside clinical evaluation, but not in patients with high clinical probability of bacterial infection 1.
From the Research
CRP and PCT in Normal TLC
- The studies provided do not directly address the normal range of CRP and PCT in relation to Total Leukocyte Count (TLC) 2, 3, 4, 5, 6.
- However, it can be inferred that CRP and PCT are biomarkers used to diagnose and monitor infections, sepsis, and inflammatory conditions 2, 3, 6.
- In patients with sepsis and septic shock, serum CRP and PCT levels are often elevated 2, 3, 6.
- A study on acute appendicitis found that TLC, CRP, and neutrophil count can be helpful in diagnosis when measured together, increasing their specificity and positive predictive value 4.
- Another study compared the utility of PCT and CRP as biomarkers of sepsis in ICU patients, finding that PCT had higher diagnostic accuracy and specificity 6.
- The normal range of CRP and PCT can vary depending on the laboratory and the specific assay used, but generally, a CRP level below 10 mg/L and a PCT level below 0.25 ng/mL are considered normal 3, 6.