Preliminary experiments were performed to determine how the concentration of BAL fluids affected recovery of D dimer and whether BAL fluids inhibited D dimer measurement by EIA. Plasma was obtained from patients with disseminated intravascular coagulation, pooled, and diluted serially with normal saline solution. The undiluted and diluted plasma samples were screened for D dimer by latex agglutination (Dimertest II Latex, American Diagnostica, NY) and were found to have D dimer at a level between 3,200 and, 6,400 ng/ml of plasma as expected for patients with disseminated intravascular coagulation.
The D dimer in the pooled plasma quantitated by EIA gave a level of 4,150 ng/ml, concurring well with the latex method. Plasma total protein concentration was measured (44 mgfail), and the plasma was diluted with normal saline solution to concentrations encompassing the range of BAL total protein levels (0.05, 0.1, 0.5, 1.0, and 5.0 mg/ml). Expected D dimer levels were calculated for each plasma dilution. The plasma preparations were concentrated 100 times in M inicon В15 concentrator chambers and D dimer levels were assayed by EIA. For plasma dilutions of 0.5,1.0, and 5 mg/ml, measured D dimer levels were 19, 12, and 22 percent, respectively, of expected levels, indicating that 78 to 88 percent of the D dimer in BAL fluids was lost during the concentration step. The D dimer was not detected in concentrates of plasma dilutions of 0.05 and 0.1 mg/ml, indicating that at some protein concentrations below 0.5 mg/ml, the recovery of D dimer was less than at higher protein concentrations. The significance of this finding is that the same level of measurable D dimer in the BAL fluids of subjects with a high BAL total protein level could go undetected in subjects with low BAL total protein.
To determine if BAL fluid inhibited the D dimer EIA, D dimer assay standards were mixed with BAL fluids from healthy individuals that were previously found to have no detectable D dimer. Treated standards assayed in parallel with untreated standards gave similar D dimer levels, indicating that BAL fluids were not inhibitory in this assay.