Researchers in Italy studied the effect of hemolysis on five commonly-ordered coagulation tests at 15 Italian hospitals.

Two-hundred-sixty-nine hemolyzed samples were tested and compared with results from non-hemolyzed samples drawn from the same patient. All samples were tested within four hours of collection. The greatest variation occurred with aPTTs and D-dimers. Fibrinogens and antithrombins were less effected, however, still to a significant degree. Protimes were only slightly influenced. 

The mean differences were as follows:

• protimes---0.1 second
• aPTTs---1.1 seconds
• D-dimers---1025 ng/mL
• fibrinogen---0.04 g/L
• antithrombin---1.4%.

The degree of hemolysis was rated "moderate to severe" in more than 95% of the samples. However, the researchers found no correlation between the degree of hemolysis and its affect on any of the four assays. Therefore, no correction factor can be reliably applied. They also found there to be no agreement between an objective visual assessment of hemolysis and the objective measurements reported by the coagulation instrument.

In conclusion, the researchers recommend continued rejection of hemolyzed samples for most coagulation tests and that visual assessments of hemolysis are unreliable. 

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