Key Concepts About Identifying Environmental Chemical Variable Names and File Locations
NHANES environmental chemical variables include laboratory measurements from blood and urine specimens. They are located in separate data files within the Laboratory section of the NHANES website for each two-year survey cycle. Data files are organized by type of specimens and chemical groups. The table below provides an example of how the data files are organized for the years 1999-2004. As evident, the availability of the chemicals differs by survey cycle.
Environmental Chemical Groups and File Names
|
Chemical Group s |
Specimen |
1999-2000 File Names |
2001-2002 File Names |
2003-2004 File Names |
|
Tobacco smoke (Cotinine) |
Serum |
LAB06 |
L06_B |
L06COT_C |
|
Metals |
|
|
|
|
|
Lead, Cadmium, Mercury |
Blood |
LAB06 |
L06_B |
L06BMT_C |
|
Heavy Metals |
Urine |
LAB06HM |
L06HM_B |
L06HM_C |
|
Mercury |
Urine |
LAB06 |
L06_B |
L06UHG_C |
|
Total Arsenic and Speciated Arsenics |
Urine |
na |
na |
L06UAS_C |
|
Persistent organic pollutants |
|
|
|
|
|
Dioxins, Furans, and Coplanar Polychlorinated Biphenyls (PCBs)
|
Serum |
LAB28POC |
L28POC_B |
L28DFP_C |
|
Non-dioxin-like Polychlorinated Biphenyls (PCBs) |
Serum |
LAB28POC |
L28POC_B |
L28NPB_C |
|
Organochlorine Pesticides |
Serum |
LAB28POC |
L28POC_B |
L28OCP_C |
|
Polybrominated Diphenyl Ethers and Polybrominated Biphenyl |
Serum |
na |
na |
L28PBE_C |
|
Polyfluoroalkyl compounds (pooled) |
Surplus Serum |
SSPFC_A * |
PFC_POOL * |
L24PFC_C |
|
Polycyclic Aromatic Hydrocarbons |
Urine |
PHPYPA |
PHPYPA_B |
L31PAH_C |
|
Phthalates |
Urine |
PHPYPA |
PHPYPA_B |
L24PH_C |
|
Phytoestrogens |
Urine |
PHPYPA |
PHPYPA_B |
L06PHY_C |
|
Pesticides |
Urine |
LAB26PP |
L26PP_B |
L26UPP_C |
|
Environmental Phenols |
Urine |
na |
na |
L24EPH_C |
|
Acrylamide and Glycidamide |
Blood |
na |
na |
L06AGE_C |
|
Perchlorate |
Urine |
na |
na |
L04PER_C |
|
Volatile Organic Compounds |
Blood |
LAB04 |
L04VOC_B |
L04VOC_C |
* Pooled serum results, not individual sample.
Phthalate Data (1999-2004): Instructive procedures and program
For the purpose of this tutorial, you can go through the procedures to download data , prepare an analytic dataset, and analyze urinary phthalates data from NHANES 1999-2004.
On each two-year survey cycle page on the NHANES website, click the Laboratory link, and then the Variable List link. Use the search feature to locate variables related to "phthalate." Note the number of environmental chemicals available and the name of the file that contains the variables. Variable names and SAS labels may change across survey cycles, so it is important to check for changes between survey cycles.
The corresponding data files for 1999-2000, 2001-2002, and 2003-2004 are PHPYPA, PHPYPA_B, and L24PH_C. Consult the documentation to determine which specific urinary phthalate metabolites were measured in each survey cycle and if there are any auxiliary variables, for example, the variable indicating the Limit of Detection for each metabolite or the urine creatinine variable. In this example, the number of urinary phthlate metabolites measured changed over three survey cycle periods: 7 were measured in 1999-2000 survey, 12 were measured in 2001-2002, and 13 were measured in 2003-2004 survey cycle. In addition, a variable indicating a comment about the Limit of Detection was included in 2003-2004 data, but not in the 1999-2000 and 2001-2002 data files for this group of environmental chemicals.
Phthalate Files and Variables
| Survey years | 1999-2000 | 2001-2002 | 2003-2004 |
|---|---|---|---|
| File name | PHPYPA | PHPYPA_B | L24PH_C |
| Variable name for Mono-(2-ethyl)-hexyl phthalate | URXMHP | URXMHP | URXMHP |
| Variable name for Mono-(2-ethyl)-hexyl phthalate comment | na | na | URDMHPLC |
