You could also look at your local coverage determination policy from the Medicare carrier you bill. Also look at Medicaid and commercial plans.
For example, Missouri Medicaid/MoHealthnet states:
http://mmac.mo.gov/update-to-physician-manual-section-13-41-e/
In order to effectively treat chronic pain, physicians rely on drug testing to monitor prescribed medications and drugs of abuse. Urine Drug Screening tests which provide qualitative or semi-quantitative initial screen or preliminary results may not be reported with a quantitative code, i.e., codes in the Therapeutic Drug Assay or Chemistry Sections of the CPT book.
Initial screening tests may be performed and billed at point of care or at independent / hospital laboratories, but not both. A second screening of the same urine specimen is considered medically unnecessary. It is the responsibility of the ordering physician to coordinate billing of initial screening tests.
Certain Medicare LCDs I believe state that 2 immunoassay screening such as one via point of care drug test cup then a secondary presumptive immunoassay on lab instrument can go against their coverage policy.
CMS NCCI policy manual points out:
https://www.cms.gov/Medicare/Coding/NationalCorrectCodInitEd/index.html
Chapter 12
12. HCPCS code G0434 (drug screen..., by CLIA waived test or moderate complexity test, per patient encounter) is utilized to report urine drug screening performed by a test that is CLIA waived or CLIA moderate complex. The code is reported with only one (1) unit of service regardless of the number of drugs screened. HCPCS code G0431 (drug screen... by high complexity test method..., per patient encounter) is utilized to report drug urine screening performed by a CLIA high complexity test method. This code is also reported with only one (1) unit of service regardless of the number of drugs screened. If a provider performs urine drug screening, it is generally not necessary for that provider to send an additional specimen from the patient to another laboratory for urine drug screening for the same drugs. For a single patient encounter only G0431 or G0434 may be reported. The testing described by G0431 includes all CLIA high complexity urine drug screen testing as well as any less complex urine drug screen testing performed at the same patient encounter. HCPCS code G0431 describes a more extensive procedure than HCPCS code G0434. Physicians should not unbundle urine drug screen testing and report HCPCS codes G0431 and G0434 for the same patient encounter.