Anti-D Titre – Serum Test
Overview
The Anti-D Titre test is a serological test used to detect and quantify anti-D antibodies in the serum of Rh-negative individuals. The D antigen is part of the Rhesus (Rh) blood group system, and when Rh-negative individuals are exposed to Rh-positive red blood cells, they may develop anti-D antibodies. This test is especially important in pregnancy management and blood transfusion safety.

Sample Type
Specimen Required: Serum

Collection Method: Blood is drawn from a vein using a sterile technique. After clotting, the sample is centrifuged to separate the serum for testing.

Purpose of the Test
To detect the presence of anti-D antibodies in Rh-negative individuals.

To monitor antibody levels during pregnancy in Rh-negative women carrying Rh-positive fetuses.

To evaluate the risk of hemolytic disease of the fetus and newborn (HDFN).

To guide decisions on Rh immunoglobulin administration and fetal monitoring.

Who Needs This Test?
Rh-negative pregnant women, especially those with a history of:

Miscarriage or abortion

Blood transfusion

Previous Rh-positive pregnancy

Individuals preparing for blood transfusions

Mothers previously sensitized to the D antigen

Testing Method
The test is usually performed using the Indirect Antiglobulin Test (IAT).

The patient's serum is serially diluted and mixed with Rh-positive red cells.

The highest dilution that still shows agglutination (clumping) is recorded as the titre.

Interpretation of Results
Negative: No anti-D antibodies detected.

Low Titre (e.g., 1:2 to 1:8): Minimal concern; routine monitoring.

Critical Titre (≥1:16 or ≥1:32):

Indicates a higher risk of HDFN.

May require intensive fetal monitoring, including Doppler ultrasound or amniocentesis.

Rising Titre: Suggests increasing antibody production and rising fetal risk.

Note: The threshold for a "critical titre" may vary depending on institutional guidelines, but a titre of 1:16 is often used as a clinical benchmark.

Clinical Significance
The test helps:

Prevent fetal complications by guiding early interventions.

Determine the need for intrauterine transfusion, early delivery, or closer surveillance.

Evaluate the effectiveness of Rh immunoglobulin given to Rh-negative mothers to prevent sensitization.

Limitations
Does not indicate the severity of fetal anemia directly.

Cannot differentiate between IgG subclasses, some of which are more harmful.

Must be interpreted along with clinical findings and ultrasound results.

Conclusion
The Anti-D Titre test is a critical tool in managing Rh incompatibility, especially in pregnancy. By measuring anti-D antibody levels in serum, it helps detect maternal sensitization early and allows for timely interventions to reduce the risk of hemolytic disease of the fetus and newborn (HDFN).