For example, if a patient had a D-dimer level of > 2.80 ug/mL and C4 level of ≤ 0.05 mg/mL, the probability of lupus activity could be computed as follows: z = -1.612 + 0.361 × 4 + 0.325 × 4 + 0.093 × 4 × 4 = 2.620. This evidence concerns the gene C4A and systemic lupus erythematosus.