This case-sensitive code system http://hl7.org/fhir/uv/genomics-reporting/CodeSystem/pharmgkb-evidence-level-custom-cs defines the following codes:

Code	Display	Definition
1A	PGKB 1A	High level of evidence. Supported by a guideline or FDA label with variant specific prescribing guidance. Additionally, supported by at least one publication.
1B	PGKB 1B	High level of evidence. But, NOT supported by a guideline or FDA label with variant specific prescribing guidance. Additionally, supported by at least one publication.
2A	PGKB 2A	Moderate level of evidence. Supported by being a KNOWN pharmacogene on https://www.pharmgkb.org/vips. Also, found in multiple studies but may have a minority of studies that did not support the majority opinion. Supported by at least two indpendent publications.
2B	PGKB 2B	Moderate level of evidence. NOT in the list of very important, KNOWN pharmacogenes. Found in multiple studies but may have a minority of studies that did not support the majority opinion. Supported by at least two indpendent publications.
3	PGKB 3	Low-level of evidence. Where either the assocation is based on a single study, failed to be reproduced, or preliminary evidence.
4	PGKB 4	The evidence does not support an association between the variant and the drug phenotype. (negative)