What are the limitations of the dat interpretation?

While the dat interpretation is highly validated, it should not replace clinical judgment. OpiCalc provides the latest evidence-based limitations for the dat interpretation to ensure safe bedside use and optimal diagnostic accuracy.

How does the dat interpretation compare to other Hematology scores?

The dat interpretation is a gold-standard diagnostic tool. OpiCalc provides side-by-side clinical guidance to help clinicians choose the most specific evidence-based tool for their patient's presentation.

Is the dat interpretation free to use?

Yes. OpiCalc provides the dat interpretation completely ad-free and optimized for mobile bedside use, ensuring you can calculate medical risk swiftly and without distraction.

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DAT Interpretation Algorithm

DAT Interpretation: The pattern of IgG and Complement (C3) reactivity on the direct antiglobulin test (Coombs) defines the class of immune haemolysis.

Guidelines & Evidence

Clinical Details

Section 1

When to Use

Differentiating the types of Autoimmune Haemolytic Anaemia (AIHA).

Investigating suspected Haemolytic Disease of the Fetus and Newborn (HDFN).

Workup for suspected acute or delayed haemolytic transfusion reactions.

Evaluating drug-induced immune haemolytic anaemia (DIIHA).

Patient Population

Any patient with biochemical features of haemolysis and a positive direct Coombs test. The pattern of reactivity (IgG vs. C3) is the primary diagnostic classifier.

When Not to Rely on This Score Alone

DAT negative AIHA — a negative DAT does not 100% exclude immune haemolysis (requires specialized assays).

Asymptomatic positive DAT — many healthy individuals or those with hyperglobulinemia have a positive DAT without haemolysis.

To monitor response to therapy — clinical and biochemical markers (Hb, LDH, Retics) are superior for monitoring treatment response.

Section 2

Formula & Logic

Patterns of Reactivity

Pattern	IgG	C3d	Possible Diagnoses
Warm AIHA	+	±	Idiopathic, SLE, CLL, Drugs
Cold Agglutinin (CAD)	-	+	Idiopathic, Mycoplasma, EBV, Lymphoma
Mixed AIHA	+	+	Idiopathic, SLE
PCH	-	+	Syphilis (classic), Viral (children)
Drug-Induced	+	±	Penicillins, Cephalosporins, NSAIDs

Section 3

Pearls/Pitfalls

Thermal Amplitude

Warm AIHA antibodies (usually IgG) react optimally at 37°C. Cold antibodies (usually IgM) fix complement (C3d) at 4°C; thus, the DAT detects the C3 remnants on the red cell, not the IgM itself which dissociates at warmer temperatures.

The Donath-Landsteiner Test

Paroxysmal Cold Haemoglobinuria (PCH) typically shows a C3-only positive DAT. Secure diagnosis requires the biphasic Donath-Landsteiner functional assay.

Section 4

Literature

Development

The DAT (Direct Coombs Test) was first described by Coombs, Mourant, and Race in 1945. It remains the foundation of immuno-hematology for detecting in-vivo sensitization of red blood cells.

Last Comprehensive Review: 2026

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