CRP vs. Sed Rate

What's the Difference?

CRP (C-reactive protein) and Sed Rate (erythrocyte sedimentation rate) are two commonly used blood tests that help in assessing inflammation in the body. While both tests are indicators of inflammation, they differ in certain aspects. CRP measures the levels of a protein produced by the liver in response to inflammation, providing a more specific and sensitive marker for acute inflammation. On the other hand, Sed Rate measures the rate at which red blood cells settle in a tube of blood, which can be influenced by various factors and may not always accurately reflect the presence or severity of inflammation. Therefore, CRP is often considered a more reliable and precise indicator of inflammation compared to Sed Rate.


AttributeCRPSed Rate
Full FormC-Reactive ProteinSedimentation Rate
IndicationInflammation, infection, tissue injuryInflammation, infection, autoimmune diseases
Speed of ResultsRapid, within hoursSlower, usually within 1-2 days
InterpretationElevated levels indicate inflammation or infectionElevated levels indicate inflammation, but not specific to the cause

Further Detail


When it comes to assessing inflammation and potential underlying health conditions, medical professionals often rely on laboratory tests to provide valuable insights. Two commonly used tests in this regard are C-reactive protein (CRP) and erythrocyte sedimentation rate (sed rate). While both tests serve as markers for inflammation, they have distinct attributes that make them useful in different clinical scenarios. In this article, we will explore and compare the attributes of CRP and sed rate, shedding light on their differences and applications.

CRP: An Overview

C-reactive protein (CRP) is a protein produced by the liver in response to inflammation. It is part of the body's immune response and plays a crucial role in the detection and elimination of pathogens. CRP levels rise rapidly during acute inflammation and can be measured through a blood test. The test measures the concentration of CRP in the blood, indicating the presence and severity of inflammation.

CRP is a highly sensitive marker, meaning it can detect even low levels of inflammation. It is often used to monitor conditions such as infections, autoimmune diseases, and cardiovascular diseases. Additionally, CRP levels can help assess the effectiveness of treatment and track disease progression.

Sed Rate: An Overview

Erythrocyte sedimentation rate (sed rate), also known as the sedimentation rate or ESR, is a test that measures how quickly red blood cells settle at the bottom of a tube over a specific period. The test indirectly assesses the presence of inflammation in the body. During inflammation, certain proteins in the blood cause red blood cells to clump together, leading to a faster sedimentation rate.

Sed rate is a non-specific marker, meaning it does not pinpoint the exact cause of inflammation. It can be influenced by various factors, including age, gender, anemia, and certain medications. However, it is still a valuable tool in diagnosing and monitoring conditions such as infections, autoimmune diseases, and certain cancers.

Comparison of Attributes

Sensitivity and Specificity

CRP is known for its high sensitivity, making it an excellent marker for detecting inflammation even at low levels. It can rise rapidly within a few hours of the onset of inflammation, allowing for early detection and intervention. On the other hand, sed rate is less sensitive and may take longer to increase in response to inflammation. It is more useful for monitoring chronic or long-term inflammation.

Speed of Results

CRP provides relatively quick results, with levels typically available within a few hours. This rapid turnaround time allows for prompt decision-making in emergency situations or acute conditions. In contrast, sed rate results take longer to obtain, usually requiring several hours or even a day. Therefore, CRP is preferred when immediate results are necessary.

Interpretation of Results

CRP levels are measured in milligrams per liter (mg/L) and are often categorized into different ranges. Higher CRP levels indicate more severe inflammation or infection. However, it is important to note that CRP alone cannot diagnose a specific condition and should be interpreted in conjunction with other clinical findings. Sed rate results are reported in millimeters per hour (mm/hr). Similarly, higher sed rates suggest the presence of inflammation, but they do not provide specific information about the underlying cause.

Factors Affecting Results

Several factors can influence CRP levels, including age, gender, obesity, smoking, and certain medications. For example, CRP levels tend to be higher in older individuals and those with obesity. On the other hand, sed rate can be affected by factors such as anemia, pregnancy, and certain chronic conditions. It is crucial for healthcare providers to consider these factors when interpreting the results of either test.

Applications in Clinical Practice

CRP is particularly useful in diagnosing and monitoring acute infections, such as bacterial or viral infections. It can also aid in assessing the response to treatment and determining the risk of complications in conditions like pneumonia or sepsis. Additionally, CRP is valuable in evaluating the risk of cardiovascular diseases, as elevated levels are associated with an increased risk of heart attacks and strokes.

Sed rate, on the other hand, is commonly employed in the diagnosis and monitoring of chronic inflammatory conditions, such as rheumatoid arthritis and systemic lupus erythematosus. It can help healthcare providers assess disease activity and guide treatment decisions. Sed rate is also used in the evaluation of temporal arteritis, a condition characterized by inflammation of blood vessels in the head and neck.


CRP and sed rate are both valuable laboratory tests that provide insights into the presence and severity of inflammation. While CRP is highly sensitive and useful for detecting acute inflammation, sed rate is more suitable for monitoring chronic or long-term inflammation. The choice between the two tests depends on the clinical context and the specific condition being evaluated. By understanding the attributes of CRP and sed rate, healthcare providers can make informed decisions and provide optimal care to their patients.

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