U01.04.013 Erythrocyte sedimentation rate

The Erythrocyte Sedimentation Rate (ESR) is a common blood test used to detect inflammation in the body. Under normal conditions, red blood cells (RBCs) are separated by negative charges, which prevent them from clumping together. However, during inflammation, products such as fibrinogen coat RBCs, reducing their negative charge and promoting RBC aggregation. These denser RBC aggregates fall faster within a pipette tube, resulting in an increased ESR. ESR is often co-tested with C-reactive protein (CRP), which is a more specific marker of inflammation.

Mechanism of ESR Increase:

Inflammatory Products: Fibrinogen and other inflammatory products reduce the negative charge on RBCs.
RBC Aggregation: Reduced charge leads to RBC clumping, forming heavier aggregates.
Increased Sedimentation: Heavier RBC aggregates fall faster in a pipette tube, raising the ESR value.

Conditions Affecting ESR

Increased ESR

ESR can be elevated in a variety of conditions, including:

Anemias: Most forms of anemia.
Infections: Systemic or localized infections.
Inflammatory Conditions: Such as giant cell arteritis and polymyalgia rheumatica.
Cancer: Metastases, multiple myeloma.
Renal Disease: End-stage renal disease or nephrotic syndrome.
Pregnancy: ESR naturally increases during pregnancy.

Decreased ESR

Conversely, ESR can be reduced in the following conditions:

Sickle Cell Anemia: The altered RBC shape hinders aggregation.
Polycythemia: Increased RBC count dilutes aggregation factors.
Heart Failure (HF): Can decrease ESR.
Microcytosis: Small RBCs reduce sedimentation rate.
Hypofibrinogenemia: Low fibrinogen levels decrease ESR.

Table: Conditions Affecting ESR

Condition	Effect on ESR
Most Anemias	Increased
Infections	Increased
Giant Cell Arteritis	Increased
Polymyalgia Rheumatica	Increased
Metastases	Increased
Multiple Myeloma	Increased
End-Stage Renal Disease	Increased
Nephrotic Syndrome	Increased
Pregnancy	Increased
Sickle Cell Anemia	Decreased
Polycythemia	Decreased
Heart Failure	Decreased
Microcytosis	Decreased
Hypofibrinogenemia	Decreased

Table: Conditions Affecting ESR

Points to Remember

ESR and Inflammation: ESR increases in response to inflammation due to RBC aggregation.
Co-Testing: ESR is often tested alongside CRP, a more specific inflammation marker.
Diagnostic Use: ESR helps in diagnosing and monitoring various conditions, but it is non-specific and should be used in conjunction with other tests.
ESR Variations: ESR values can be influenced by multiple factors, including anemia, infections, cancer, and pregnancy.

USMLE Step 1 Review Series

Curriculum

U01.04.013 Erythrocyte sedimentation rate

Mechanism of ESR Increase:

Conditions Affecting ESR

Increased ESR

Decreased ESR

Table: Conditions Affecting ESR

Points to Remember

Modal title