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In two studies of HAA² exposure in humans (1, 2), we expressed urinary HAA levels in units of creatinine due to the fact that 8 h urine samples were being analyzed. In his letter, Dr. W. Pfau takes issue with this approach, arguing that individual creatinine values are influenced by recent meat consumption. He presents a hypothetical example of two individuals with similar levels of HAA exposure: one (subject A) with relatively low intake of heavily cooked meat; and (b) the other (subject B) with a higher intake of lightly browned meat. Our method of adjustment would create a spurious difference in HAA excretion level between the two subjects in that subject B will show a lower HAA value than subject A.

We have reanalyzed the data sets in the studies cited above using the actual values of urinary HAA excretion (i.e., without creatinine adjustment; all units in pg/ml). Our results show that among whites and Asian Americans, PhIP values, with or without adjustment,are quite similar; in whites, the unadjusted mean is 1.14, whereas the adjusted mean is 1.18. In Asian Americans, the unadjusted mean is 3.12,whereas the adjusted mean is 3.33. This is not the case in the African Americans; the unadjusted mean is 28% higher than the adjusted mean(4.29 versus 3.36). The same holds true for MeIQx; the unadjusted mean in African Americans is 34% higher than the adjusted mean (5.07 versus 3.78). Based on unadjusted means, African Americans clearly possess the highest levels of HAAs, with intermediate and lowest values in Asian Americans and whites, respectively. These data of the unadjusted HAA means among the three groups are given in Table 1. Our results show that with or without adjustment, HAA values are statistically different across the three racial/ethnic groups.

Adjustment has relatively little influence on the interrelationship between PhIP and MeIQx values within individuals. With adjustment, we found perfect concordance among the subjects to be 47% (Table 3 in Ref. 2). Without adjustment, the degree of perfect concordance is slightly lower (41%). However, extreme discordance also decreased from 8% based on adjusted values to 5% using unadjusted values.

With or without adjustment, there is no association between urinary PhIP level and intake frequencies of various meats (Table 4 in Ref. 2). Also, with or without adjustment, there are no associations between urinary PhIP level and NAT2 phenotype, cigarette smoking, and intake of selected types of vegetables. Without adjustment, the association between MeIQx excretion and intake frequencies of various meats is in accord with the earlier study (Table 2 in Ref. 1), showing a relatively higher MeIQx exposure in frequent consumers of pork (including bacon),a lower MeIQx exposure in frequent consumers of pork (including bacon),and a lower MeIQx exposure in frequent consumers of chicken.