A primary caretaker is a potential reservoir of bacteria for an infant child and can be evaluated during a child's caries risk assessment. The aim of this study was to investigate an indirect method for assessing Streptococcus mutans and Streptococcus sobrinus (MS) and lactobacillus (LB) levels in a caretaker's saliva. Thirty-eight primary caretakers participated in the study to determine whether a 2-step method to assess the intracellular adenosine triphosphate (ATP) levels in saliva (saliva i-ATP method) predicted higher MS and LB levels. This method was tested against a 1-step swab-based total ATP testing of dental plaque (plaque t-ATP method). Receiver operating characteristic (ROC) curves were used to examine the relationship between specificity and sensitivity of the two diagnostic tests. Although the area under the ROC curves of both the saliva i-APT (0.823) and the plaque t-ATP (0.774) methods were shown to be statistically different (p <.05) than the null hypothesis test of a random coin flip, the diagnostic predictability of the ATP tests to assess high levels of MS and LB remained low. The optimal cutoff, which was defined by the Youden index, for the saliva i-ATP method produced a sensitivity/specificity of 60.7/100.0 for MS and 78.6/88.9 for LB. Applying these results to populations of low or high bacterial level prevalence produced undesirable positive and negative predictive values for future potential patients. A pair-wise comparison of both area under the ROC curve values of the saliva i-ATP and plaque t-ATP did not find a statistically significant difference in using one test over the other (MS, p =.629; LB, p =.737). The findings of this study can educate dental clinicians that diagnostic tests, such as the 2-step saliva i-ATP method, can be found to be statistically significant but not ideal for patient use in terms of diagnostic predictability.