Table of Contents

Locator Record

Title: Unmetabolized Folic Acid (Surplus Sera) (SSFOL_A )
Contact Number: 1-866-441-NCHS
Years of Content: 1999 - 2000
First Published: October, 2009
Revised: July, 2010
Access Constraints: None
Use Constraints: None
Geographic Coverage: National
Subject:Unmetabolized folic acid
Record Source: NHANES 1999 - 2000
Survey Methodology: NHANES 1999 - 2000 is a stratified multistage probability sample of the civilian non-institutionalized population of the U.S.
Medium: NHANES Web site; SAS transport files

Component Description

Measurement of unmetabolized folic acid from stored sera specimens from NHANES 1999-2000 in participants >= 60 years of age.

Eligible Sample

Participants >= 60 years of age from NHANES 1999-2000 with stored sera.

Description of Laboratory Methodology

Measurement of Unmetabolized Folic Acid in Serum. Folic acid and 5MeTHF concentrations were determined using the affinity/HPLC method with electrochemical (coulometric) detection method Which was developed by us at the USDA Human Nutrition Research Center at Tufts University (Bagley et al., 1997; Kalmbach et al., 2008) with the following modifications to increase throughput and precision. Serum samples (0.2 mL) were diluted with 1.2 mL of 50mM potassium tetraborate in 1% sodium ascorbate and vortexed. Twenty picomoles of ethyltetrahydrofolate (eTHF) was added as an internal standard. The mixture was boiled for 30 minutes and then cooled on ice and kept covered overnight at 4° C. The mixture was centrifuged for 20 minutes at 4° C at 36,000xg and filtered. An aliquot (0.9ml) of the supernatant fraction was injected onto the affinity/HPLC system. The revised affinity/HPLC system consisted of two affinity columns, containing immobilized folate binding protein (FBP), that were connected via a 10 port, two position switching valve to an analytical column (Betasil Phenyl 250 x 4.6 mm; Keystone Scientific). This allows one affinity column to be loaded with the sample and subsequently washed with a pH 7.0 phosphate buffer, while the second is eluted into the analytical column with an acetonitrile gradient at acid pH and into the electrochemical detector. At the end of the run, a signal is sent to switch the direction of the mobile phases to allow the elution of the loaded column for folate analysis and simultaneous loading of the second column with the new sample. Folate activity was determined by using an ESA Four Channel Coularray Detector set at 0, 300, 500 and 600mV. Quantification and identification of individual folates was done by comparison to external and internal folate standards of known concentration. Limit of detection was 0.18 pmol/ml for 5-methyltetrahydrofolate and folic acid. Recovery was 92.2% (5-methyltetrahydrofolate) and 98.9% (folic acid). CV’s for samples ran alone or spiked with 5, 10, and 20 pmol of folate were 5.2-8.6% for 5-methyltetrahydrofolate (within day) and 3.2-6.3 (between days) and for folic acid 5.3-6.4% (within day) and 3.5-7.3 (between days). Run time for the HPLC was reduced to 30 min per sample (40-45 samples analyzed per 24 hours).

Total folate determined by this method highly correlated (r2=0.93, p< 0.001) with values obtained by the microbial assay

Data Processing and Editing

Data was received after all the laboratory testing was complete. The data were not edited.
Data Access: All data are publicly available.

Laboratory Quality Assurance and Monitoring

See description above.

Analytic Notes

There are 7 variables:
SEQN=Respondent sequence number
SSMETSI=Methyltetrahydrofolate (pmol/ml) 
        Value Range: (1.57-291.03)
SSFOLSI=Folic Acid (pmol/ml) 
        Value Range: 0=undetectable, 
        Value Range: (0.185 -272.99)
SSFOLTSI=Total Folate (pmol/ml) 
        Value Range: (1.57-432.61)
SSMET=Methyltetrahydrofolate (ng/ml) 
        Value Range: (0.69-128.34)
SSFOL=Folic Acid (ng/ml) 
        Value Range: 0=undetectable, 
        Value Range: (0.082 -120.39)
SSFOLTOT=Total Folate (ng/ml) 
        Value Range: (0.69-190.78)

References

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:
SEQN
SAS Label:
Respondent sequence number
English Text:
Respondent sequence number.
Target:
Both males and females 60 YEARS - 150 YEARS

SSMETSI - Methyltetrahydrofolate pmol/ml

Variable Name:
SSMETSI
SAS Label:
Methyltetrahydrofolate pmol/ml
English Text:
Methyltetrahydrofolate pmol/ml
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1.5737312812 to 205.19886608 Range of Values 1353 1353
. Missing 1 1354

SSFOLSI - Folic Acid pmol/ml

Variable Name:
SSFOLSI
SAS Label:
Folic Acid pmol/ml
English Text:
Folic Acid pmol/ml
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 272.98746201 Range of Values 1354 1354
. Missing 0 1354

SSFOLTSI - Total Folate pmol/ml

Variable Name:
SSFOLTSI
SAS Label:
Total Folate pmol/ml
English Text:
Total Folate pmol/ml
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1.5737312812 to 432.61322188 Range of Values 1353 1353
. Missing 1 1354

SSMET - Methyltetrahydrofolate ng/ml

Variable Name:
SSMET
SAS Label:
Methyltetrahydrofolate ng/ml
English Text:
Methyltetrahydrofolate ng/ml
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.694015495 to 90.49269994 Range of Values 1353 1353
. Missing 1 1354

SSFOL - Folic Acid ng/ml

Variable Name:
SSFOL
SAS Label:
Folic Acid ng/ml
English Text:
Folic Acid ng/ml
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 120.38747074 Range of Values 1354 1354
. Missing 0 1354

SSFOLTOT - Total Folate ng/ml

Variable Name:
SSFOLTOT
SAS Label:
Total Folate ng/ml
English Text:
Total Folate ng/ml
Target:
Both males and females 60 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.694015495 to 190.78243085 Range of Values 1353 1353
. Missing 1 1354