Can hemolysis of a blood sample cause false elevated results of lactate dehydrogenase (LD) and D-dimer?

Hemolysis Effects on Lactate Dehydrogenase and D-Dimer

Yes, hemolysis causes falsely elevated lactate dehydrogenase (LD) results even at visually undetectable levels, while D-dimer is affected at moderate to high hemolysis levels, making both tests unreliable in hemolyzed samples.

Lactate Dehydrogenase (LD) - Highly Sensitive to Hemolysis

LD is one of the most hemolysis-sensitive analytes and becomes falsely elevated at extremely low levels of hemolysis that cannot be detected by visual inspection alone. 1

Critical Thresholds for LD Interference

• LD shows clinically meaningful interference at plasma hemoglobin concentrations <0.5 g/L, which corresponds to hemolysis that is essentially invisible to the naked eye 1
• This occurs because red blood cells contain approximately 150 times more LD than plasma, making even minimal cell lysis catastrophic for accurate measurement 1
• Samples should be rejected for LD testing when the hemolysis index (H-index) indicates any detectable hemolysis, as the analytically significant bias occurs before clinically significant bias can be assessed 2

Mechanism of LD Elevation

• Red blood cells are extraordinarily rich in LD (particularly LDH1 and LDH2 isoenzymes), and their rupture releases massive amounts of this enzyme into the surrounding plasma 1
• The interference is mechanical and unavoidable - there is no correction formula that can reliably adjust for hemolysis effects on LD 2

Practical Management

• Automatic measurement of H-index is essential rather than relying on visual inspection, as LD interference occurs below the threshold of visual detection 2
• When H-index values reach ≥10 g/L hemoglobin, all laboratory data become unreliable and should be suppressed entirely 2
• The only acceptable solution is to reject the sample and request recollection - corrective formulas are discouraged due to inaccuracy and imprecision 2

D-Dimer - Moderately Sensitive to Hemolysis

D-dimer testing is affected by hemolysis, but requires higher levels of hemolysis than LD to produce clinically significant interference.

Critical Thresholds for D-Dimer Interference

• D-dimer results remain reliable up to hemolysis index +2 (hemoglobin 1.01-2 g/L) for most assays, though this varies by manufacturer 3
• At hemolysis index +2 and above, D-dimer samples should be rejected as "hemolyzed sample" to ensure accuracy 3
• Some manufacturer information may underestimate hemolysis interference - one study found the Improgen kit was affected at lower hemolysis levels than stated in the package insert (which claimed tolerance up to hemoglobin >5 g/L) 3

Assay-Specific Variability

• Different D-dimer assays use different monoclonal antibodies to fibrin fragments, creating substantial variability in hemolysis susceptibility between manufacturers 4
• The Fibrin Assay Comparison Trial demonstrated considerable variations in specificity for crosslinked fibrin across 12 different D-dimer manufacturers 4
• Laboratories must validate hemolysis interference under their own conditions rather than relying solely on manufacturer specifications 3

Mechanism of D-Dimer Interference

• While the exact mechanism is not fully elucidated in the provided evidence, hemolysis likely interferes through release of cellular components that cross-react with the monoclonal antibodies used in D-dimer assays 4
• Fibrin degradation products (FDPs) and other fragments can cause over- or underestimation of D-dimer depending on the specific assay methodology 4

Practical Management

• Samples with hemolysis index +2 or higher should be rejected for D-dimer testing and a new sample requested 3
• When H-index indicates moderate hemolysis (1.01-2.50 g/L hemoglobin), results can potentially be released with a comment describing potential bias and recommending recollection if the variation might exceed the reference change value 2
• For critical clinical decisions (such as ruling out pulmonary embolism or deep vein thrombosis), never rely on D-dimer results from visibly hemolyzed samples - always request a new specimen 5

Common Pitfalls to Avoid

• Never use visual inspection alone to assess hemolysis for LD testing - automated H-index measurement is mandatory 2
• Do not apply correction formulas to adjust for hemolysis interference in either LD or D-dimer - these are unreliable and should be avoided 2
• Verify manufacturer claims about hemolysis tolerance under your own laboratory conditions, as package insert information may be inaccurate 3
• For D-dimer specifically, remember that a positive result cannot confirm thrombosis regardless of sample quality - imaging confirmation is always required before anticoagulation 5
• When hemolysis is severe (H-index ≥10 g/L), suppress all results rather than attempting selective reporting 2