Rapid quantitative evaluation of plasma D-dimer levels in thrombotic states using an automated latex photometric immunoassay.

To evaluate a recently developed latex photometric immunoassay (LPIA) that which can measure 40 samples quantitatively within 30 minutes, we measured D-dimer levels in blood samples obtained from patients with disseminated intravascular coagulation (DIC). Linearity of D-dimer determination was shown over the range from 0.5 to 36 micrograms/ml, and recovery studies demonstrated 94 to 108% recovery. The intra-assay and inter-assay coefficients of variation ranged from 0.6 to 11.3% at plasma D-dimer levels of 0.54 to 30.1 micrograms/ml. No interference by lipids, bilirubin, haemoglobin, rheumatoid factor, or gamma-globulin was noted. The normal D-dimer range was less than 0.5 microgram/ml in healthy ambulatory subjects, while the level in elderly subjects with atherosclerosis (14%) or in immobilized subjects (38%) was well above this limit. There was a strong correlation between plasma and serum D-dimer levels (r = 0.993). D-dimer levels measured by this LPIA showed a good correlation with those determined using two kinds of ELISA. The LPIA D-dimer levels were elevated in some subjects with diseases predisposing to DIC, but remained below 10.0 micrograms/ml. On the other hand, the LPIA D-dimer levels in DIC subjects were almost always above 10.0 microgramS/ml. Our study showed that a hypercoagulable state should be suspected when the LPIA D-dimer level is greater than 0.5 microgram/ml and that DIC should be diagnosed when the level is greater than 10.0 micrograms/ml in the presence of an appropriate underlying disease. This LPIA system can rapidly evaluate the presence of a hypercoagulable state as accurately as any ELISA, and thus seems potentially valuable for both emergency and routine laboratory use.