Haemolysis Screen Interpreter — LDH, Haptoglobin, Retics, DAT
Haemolysis Screen Interpreter — LDH, Haptoglobin, Retics, DAT
Enter the haemolysis screen — LDH, haptoglobin, reticulocytes, unconjugated bilirubin and the direct antiglobulin test — with the film, urine, inflammation, recent transfusion and whether the sample itself was haemolysed. It says whether haemolysis is likely, then immune or non-immune and intravascular or extravascular, and it catches the two classic traps: a haemolysed sample, and a haptoglobin held up by inflammation.
Haemolysis screen
LDH + haptoglobin + retics + DAT → patternLDH raised (below 4 × ULN), haptoglobin low, reticulocytes raised, unconjugated bilirubin raised, DAT IgG positive, spherocytes, no haemoglobinuria, no inflammation, sample not haemolysed, not transfused
What each marker does, and what fools it
| Marker | In haemolysis | False positive | False negative |
|---|---|---|---|
| LDH | Raised; about 4–5 × ULN when intravascular | Tissue damage, tumours, a haemolysed sample | Mild extravascular haemolysis |
| Haptoglobin | Low or undetectable | Liver impairment, malnutrition, congenital deficiency | Inflammation, smoking, nephrotic syndrome hold it up |
| Reticulocytes | Raised | Bleeding, recovery from deficiency | About 20% of adults with AIHA have reticulocytopenia |
| Unconjugated bilirubin | Raised | Gilbert’s syndrome | Mild haemolysis |
| DAT | Positive in immune haemolysis | Healthy people, hospital patients, IVIG, recent transfusion | DAT-negative AIHA |
Is it haemolysis, is it immune, and where are the cells breaking?
No single test diagnoses haemolysis. The screen combines markers of red cell breakdown — LDH, unconjugated bilirubin, and haptoglobin, which binds free haemoglobin and is consumed — with a marker of the marrow’s response, the reticulocyte count. Haptoglobin is the most discriminating: in Marchand’s 1980 study a level of 25 mg/dL or less separated haemolytic from other disorders with a sensitivity of 83% and a specificity of 96%.
The laboratory trap comes first. A sample that haemolyses in the tube releases LDH and potassium and looks like haemolysis in the patient. The haemolysis index flags it but cannot say where it happened; a normal haptoglobin says it was the tube, a low one says it may have been the patient. See the haemolysis, icterus and lipaemia interpreter.
The clinical trap is inflammation. Haptoglobin is an acute-phase protein, raised by inflammation, smoking and nephrotic syndrome, and that can mask haemolysis (Barcellini 2015). Reticulocytes mislead too: about a fifth of adults with autoimmune haemolysis have a low count.
Once haemolysis is established, the DAT separates immune from non-immune — IgG for warm autoimmune haemolysis, C3d alone for cold antibodies — and the film and urine separate intravascular from extravascular. Fragments mean microangiopathy and are urgent. For the numbers, see the absolute reticulocyte count calculator, haptoglobin unit converter and indirect bilirubin calculator.
Frequently asked questions
What tests confirm haemolysis?
A combination: raised LDH, raised unconjugated bilirubin and raised reticulocytes, with a low haptoglobin. Haptoglobin is the most specific single marker; the direct antiglobulin test and the blood film then show the cause.
Can haptoglobin be normal in haemolysis?
Yes. Haptoglobin is an acute-phase protein and rises with inflammation, smoking and nephrotic syndrome, which can mask haemolysis. A normal haptoglobin in an inflamed patient is less reassuring than in a well one.
Can a haemolysed blood sample raise LDH and potassium?
Yes. Red cells broken in the tube release LDH and potassium, raising both with nothing wrong with the patient. A normal haptoglobin points to the tube; a low haptoglobin suggests the haemolysis may be in the patient.
What does a positive DAT mean?
Antibody or complement is coating the red cells. With haemolysis, IgG suggests warm autoimmune haemolytic anaemia and C3d alone a cold antibody; after a recent transfusion, a delayed transfusion reaction. Without haemolysis, a positive DAT is common and does not by itself mean disease.
How do you tell intravascular from extravascular haemolysis?
Intravascular haemolysis releases haemoglobin into the circulation: LDH around 4–5 times the upper limit, haemoglobinuria and haemosiderinuria, undetectable haptoglobin. Extravascular haemolysis happens in the spleen and liver, with a milder LDH rise and often spherocytes.
Related calculators
References
- Barcellini W, Fattizzo B. Clinical applications of hemolytic markers in the differential diagnosis and management of hemolytic anemia. Dis Markers. 2015;2015:635670. — haptoglobin "increases in inflammatory diseases, in cigarette smokers, and in nephrotic syndrome, possibly masking an underlying hemolytic condition"; reduced haptoglobin also in "liver impairment, malnutrition, and congenital hypohaptoglobinemia"; LDH "slightly increased" in extravascular haemolysis and "4-5-fold the upper normal limit" in intravascular; reticulocytopenia in about 20% of adults with autoimmune haemolytic anaemia; DAT-negative cases often severe.
- Marchand A, Galen RS, Van Lente F. The predictive value of serum haptoglobin in hemolytic disease. JAMA. 1980;243(19):1909–1911. — haptoglobin of 25 mg/dL or less separated haemolytic from non-haemolytic disorders with sensitivity 83% and specificity 96% (as quoted by Barcellini 2015).
- Hill QA, Stamps R, Massey E, et al. The diagnosis and management of primary autoimmune haemolytic anaemia. Br J Haematol. 2017;176(3):395–411. — the British Society for Haematology guideline; classification of autoimmune haemolysis by the direct antiglobulin test (IgG, C3d). Cited for the classification; specific statements on this page are sourced to Barcellini 2015.
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/