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Audit of Claims Submitted by Dr. Khuong Nguyen to MassHealth Objectives, Scope and Methodology

An explanation of what the audit examined and how it was conducted.

Table of Contents


In accordance with Section 12 of Chapter 11 of the Massachusetts General Laws, the Office of the State Auditor (OSA) has conducted a performance audit of certain activities of Dr. Khuong Nguyen for the period July 1, 2011 through December 31, 2016.

We conducted this performance audit in accordance with generally accepted government auditing standards. Those standards require that we plan and perform the audit to obtain sufficient, appropriate evidence to provide a reasonable basis for our findings and conclusions based on our audit objectives. We believe that the evidence obtained provides a reasonable basis for our findings and conclusions based on our audit objectives.

Below are the question we intended our audit to answer, the conclusion we reached regarding our objective, and where the objective is discussed in the audit findings.




  1. Did Dr. Nguyen properly bill MassHealth for vision care services he provided to its members?

No; see Findings 1, 2, and 3

We gained an understanding of the control environment at Westborough Eye Care and evaluated the controls over billing processes we deemed significant to our audit objective.

To perform our audit procedures, we obtained from the state’s Medicaid Management Information System (MMIS) all data for claims paid by MassHealth to Dr. Nguyen. We relied on the work performed by OSA in a separate project that tested certain information system controls in MMIS, which is maintained by the Executive Office of Health and Human Services. As part of the work performed, OSA reviewed existing information, tested selected system controls, and interviewed knowledgeable agency officials about the MMIS claim data. Additionally, we performed other validity and integrity tests on all claim data for this audit, including (1) testing for missing data, (2) scanning for duplicate records, (3) looking for dates outside specific time periods, and (4) tracing a sample of claims queried to source documents. Based on these procedures, we determined that the claim data obtained from MMIS were sufficiently reliable for the purposes of this audit.

Through interviews with Dr. Nguyen, we learned that he has traveled to Department of Youth Services (DYS) facilities and Department of Children and Families (DCF) programs throughout the Commonwealth to provide vision care to youths in DYS and DCF custody. We interviewed DYS and DCF officials to gain an understanding of their experience working with Dr. Nguyen when he provided vision care to youths in their custody, including asking them about any policies and procedures for allowing medical professionals into their facilities. We also requested medical service contracts for the vision care provided by Dr. Nguyen.

We selected a statistically random sample of 180 out of 18,130 paid vision care claims from the audit period, using an expected error rate of 50%, a desired precision range of 15%, and a confidence level of 95%, to determine whether Dr. Nguyen properly billed MassHealth for these services. Expected error rate is the anticipated rate of occurrence of the error of improper billing for services; 50% is the most conservative. Desired precision is a measure of how precise the actual error rate is. Confidence level is the numerical measure of how confident one can be that the sample results reflect the results that would have been obtained if the entire population had been tested. For this audit, we designed our sample so that we would be 95% confident that the actual error rate in the sample of 180 vision care claims would be within a range of +/- 7.5%, or 15% (point estimate), of the error in the population of 18,130 claims.

To determine whether Dr. Nguyen properly billed MassHealth for vision care, we reviewed information in members’ medical records for the sampled claims, including the servicing provider name, date of service, description of chief complaint, documentation of physical examinations, review of physiological systems, and medical decision-making.

The statistical sampling method described above allows us to extrapolate the sampled findings to the entire population of vision care claims paid. We did not project any identified errors to the population of vision care services for Finding 1 because we extrapolated these errors in Finding 3 and we performed 100% testing of all dispensing services for Finding 2. For Finding 3, the actual error rate in our sample was 21.67%, and when projecting this to the total population of paid vision care claims, we are 95% confident that at least 16.74% (at the lower limit) or at most 27.30% (at the upper limit) of Dr. Nguyen’s vision care claims were overpaid. In OSA’s opinion, the lower limit (the most conservative amount), 16.74%, is the minimum amount that Dr. Nguyen must repay to the Commonwealth.

Since Dr. Nguyen did not maintain complete medical records at his office documenting services provided to members residing in DYS facilities and DCF programs, contrary to MassHealth recordkeeping requirements, we performed the following additional procedures to verify that he performed the vision care services at those locations:

  • We interviewed DYS and DCF nurse managers and other DYS and DCF officials about their processes and procedures for obtaining Dr. Nguyen’s services. We also had discussions with DYS officials, and performed our own additional research, on DYS’s requirement that people entering its facilities successfully complete training on the Prison Rape Elimination Act of 2003.
  • For a judgmental sample of seven DYS facilities, we reviewed visitor logbooks and operations logbooks (a total of 69 logbooks) for evidence that Dr. Nguyen actually entered the facilities to provide vision care to the members for whom he billed. All DYS facilities maintain a visitor logbook that requires visitors, including medical professionals, to sign in and out when visiting. Additionally, DYS staff members maintain an operations logbook, updated for each resident in 15-minute increments, that is signed daily by all DYS staff members on a shift. This logbook tracks the location of each youth in custody and notes all visitors who come into contact with each youth, including medical professionals.
  • For a judgmental sample of three DCF programs, we interviewed program directors and obtained and reviewed medical documentation supporting vision care provided by Dr. Nguyen to youths in DCF custody.
  • For the 39 out of the 180 sampled claims that were billed using procedure codes 99328 and 99337 for services provided to DYS and DCF youths, we obtained and reviewed Dr. Nguyen’s supporting documentation from the facilities and programs. Our review consisted of examining whether Dr. Nguyen properly documented the services provided and included all of the required components when billing for a higher-complexity evaluation and management service in accordance with the Centers for Medicare and Medicaid Services’ 1995 Documentation Guidelines for Evaluation and Management Services.

To determine whether Dr. Nguyen properly billed for dispensing services, we performed the following tests:

  • We compared all dispensing service claims to orders for materials for the same member to determine whether Dr. Nguyen placed the material order with MassHealth’s optical supplier, Massachusetts Correctional Industries, and reviewed the timing of when he submitted a claim for dispensing services.
  • We reviewed all dispensing claim data to determine whether Dr. Nguyen billed for multiple dispensing orders when only one pair of eyeglasses was ordered.
  • For all DYS and DCF youths who received eyeglasses, we confirmed with DYS and DCF officials and with Dr. Nguyen himself that he mailed the eyeglasses to the facilities and programs.
Date published: July 16, 2018