11/08/2026
🧪 TUESDAY LAB UPDATE | C-REACTIVE PROTEIN (CRP) TEST 🩸
🔬 WHAT IS CRP?
C-Reactive Protein (CRP) is an acute-phase protein synthesized primarily by the liver. Its concentration in the blood increases in response to inflammatory processes, particularly following stimulation by inflammatory cytokines such as IL-6.
CRP is one of the most commonly used laboratory biomarkers for detecting and monitoring systemic inflammation, infection, and tissue injury.
Unlike ESR, CRP generally responds more rapidly to changes in inflammation, making it useful for assessing the current inflammatory state and monitoring changes over time.
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🎯 CLINICAL PURPOSES OF CRP TESTING
CRP measurement may be requested to:
🔹 Detect and assess the presence of systemic inflammation
🔹 Support the evaluation of suspected bacterial or other infections
🔹 Assess the severity of inflammatory conditions
🔹 Monitor disease activity in autoimmune and inflammatory disorders
🔹 Monitor response to treatment
🔹 Help detect complications or worsening inflammation
🔹 Assist in the clinical assessment of tissue injury and some postoperative complications
⚠️ CRP is a non-specific marker. An elevated result indicates inflammation but does not, by itself, identify the underlying cause or location.
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🧫 SPECIMEN REQUIREMENT
The specimen depends on the analytical method used.
Common specimens:
• Serum
• Plasma, where validated by the laboratory method
For serum testing, venous blood is collected into an appropriate plain or serum-separator tube and allowed to clot before centrifugation.
Proper specimen identification, collection, processing, storage, and handling are essential for reliable results.
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⚙️ PRINCIPLE OF CRP TESTING
CRP can be measured using different analytical techniques, including:
🔬 Immunoturbidimetry
🔬 Latex agglutination
🔬 Nephelometry
🔬 Other automated immunoassay methods
In an immunoturbidimetric or latex-enhanced method, CRP in the patient's sample reacts with specific anti-CRP antibodies. The resulting immune complexes produce changes in turbidity or light scattering that are measured by the analyzer.
The measured signal is proportional to the concentration of CRP in the sample within the assay's analytical range.
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🧪 BASIC LABORATORY PROCEDURE
Using an automated immunoturbidimetric method:
1️⃣ Collect and properly identify the patient's blood specimen.
2️⃣ Process the specimen to obtain serum or appropriate plasma.
3️⃣ Load the sample and required reagents according to the manufacturer's instructions.
4️⃣ The analyzer combines the specimen with CRP-specific reagent.
5️⃣ Antigen-antibody complexes are formed.
6️⃣ The analyzer measures the resulting optical change.
7️⃣ The instrument calculates and reports the CRP concentration, commonly in mg/L.
📌 Important: Exact reagent volumes, incubation times, wavelengths, calibration procedures, quality-control requirements, and reference intervals depend on the specific analyzer and reagent manufacturer's instructions.
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📊 HOW SHOULD CRP RESULTS BE INTERPRETED?
CRP reference intervals are method- and laboratory-dependent, so the laboratory's validated reference range should always be used.
Generally:
🔹 Normal/low CRP: No significant systemic inflammatory response is detected at the time of testing.
🔹 Mild elevation: May occur with mild inflammation, infection, chronic inflammatory conditions, or other causes.
🔹 Moderate to marked elevation: May be associated with significant inflammation, infection, tissue injury, or autoimmune disease.
🔹 Very high CRP: Can occur in severe bacterial infections and other major inflammatory or tissue-injury states.
⚠️ A CRP result should never be interpreted in isolation.
Clinical interpretation should consider the patient's:
• Signs and symptoms
• Medical history
• Duration of illness
• FBC/CBC findings
• ESR
• Microbiological results
• Other relevant biochemical and immunological investigations
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🦠 CRP AND INFECTION
CRP can increase significantly during acute bacterial infections, but an elevated CRP does not prove that an infection is bacterial.
Viral infections can also produce elevated CRP, particularly when inflammation is substantial.
Therefore, CRP should not be used alone to distinguish bacterial from viral infection.
It is most useful when interpreted alongside clinical findings and other investigations.
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📈 CONDITIONS THAT MAY INCREASE CRP
CRP may be elevated in:
• Bacterial and viral infections
• Autoimmune diseases
• Rheumatoid arthritis
• Systemic lupus erythematosus
• Vasculitis
• Tissue injury or trauma
• Surgery
• Some malignancies
• Cardiovascular inflammatory conditions
• Other acute or chronic inflammatory disorders
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❤️ WHAT IS hs-CRP?
High-sensitivity CRP (hs-CRP) is a more sensitive assay designed to detect low concentrations of CRP.
It is primarily used in specific clinical contexts, particularly cardiovascular risk assessment, rather than as a general replacement for conventional CRP testing.
The interpretation of hs-CRP is different from conventional CRP and should follow the applicable clinical guidelines.
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⚠️ FACTORS THAT CAN AFFECT CRP
CRP concentrations can be influenced by:
• Acute infection
• Chronic inflammation
• Obesity and metabolic factors
• Smoking
• Tissue injury
• Pregnancy
• Certain medications
• Age and other patient-related factors
Therefore, laboratory results must always be interpreted in the appropriate clinical context.
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🧠 MLT TAKE-HOME MESSAGE
CRP is a sensitive but non-specific biomarker of inflammation.
Its greatest clinical value is not simply in identifying an elevated result, but in helping healthcare professionals assess inflammatory activity and monitor changes over time.
A falling CRP may indicate a reduction in inflammatory activity or response to treatment, while a persistently elevated or rising CRP may warrant further clinical assessment.
🔬 The laboratory does more than produce numbers—we provide reliable information that supports clinical decision-making.
🩸 Accurate Testing. Reliable Results. Better Patient Care.
