Link to other blood tests

Prepared by: Ben Schöttker, German Cancer Research Center, Clinical Epidemiology and Ageing research, Heidelberg, Germany

Contents:

1. Summary of lung function assessment in cohorts
2. Harmonized vitamin D variables
3. Availability of eligible data in cohorts for the harmonized vitamin D variables
4. Additional comments
5. Missing information
6. References

1. Summary of vitamin D assessment in cohorts

Details of collected information about vitamin D measurement from the CHANCES cohorts are displayed in the attached Excel table.

Eight cohorts have vitamin D data (EPIC-ELDERLY, ESTHER, MORGAM, UOR, NHS, RES, SENECA and Zutphen). ESTHER is the only cohort with repeated measures.

Cohorts show the following common ground:

• 25(OH)-vitamin D has been measured.
• Vitamin D has been measured from frozen stored serum samples. Exception: In NHS vitamin D was measured from plasma samples within 48 hours after blood donation.
• The date of blood donation is known, so that seasonal changes in vitamin-D-levels can be taken into account.

Cohorts vary in the following:

• Other types of vitamin D than 25(OH)-vitamin D are available in UOR, only.
• Apparatus and assays used vary: Radioimmunoassay in NHS and Zutphen; Immunoassay in ESTHER and MORGAM and protein-binding assay in SENECA.
• Temperature for sample storage varied from -20°C to -80°C.
• UOR is not a random sample of a general population and the NHS and EPIC-ELDERLY Greece have vitamin D data only for specific disease-defined sub-populations plus controls.

2. Harmonized vitamin D variables

The following vitamin D variables have been defined in document Definitions of variables:

• BLOOD_VITD - 25(OH) Vitamin D
• BLOOD_VITD_MO - Month of blood donation for Vitamin D measurements

3. Availability of eligible data in cohorts for the harmonized vitamin D variables

The variables are codable for all seven cohorts for at least one contact. Repeated measures are available in ESTHER.

Table 8 – Number of available vitamin D measurements in CHANCES cohorts for general population analyses

Notes: UOR is not listed because it doesn’t reflect a general population sample. NHS is not listed because vitamin D was only measured for nested case control studies for subjects with hypertension, colon cancer, breast cancer and colorectal adenoma and EPIC-ELDERLY Greece because only measures for colorectal, breast, lymphoma and prostate cancer sites are available.

4. Additional comments

• The differences of assays (and maybe storage-conditions of blood samples) will have resulted in incomparable vitamin D assessments (14). The assays have been calibrated to different references because only since the end of 2009 a gold standard became available for 25(OH)-vitamin D assay calibration (15;16). A promising way for CHANCES would be to calibrate the assays used in the different CHANCES cohorts with the new standard calibration solution for 25(OH)-vitamin D2 and D3 (17). If this will not be done, parallel analyses in individual cohorts are strongly recommended with percentile-based cut-offs in each cohort and avoidance of defined cut-points for 25(OH)-deficiency such as 50 nmol/l.
• The UOR is not a general population sample and can not be pooled with other cohorts.
• The NHS and EPIC-ELDERLY GREECE can not be used for general population analyses because vitamin D was only measured for nested case control studies.

5. Missing information

• Assay type and apparatus used in RES and UOR; apparatus used in SENECA and NHS.
• Serum used in UOR?

References

Collected information on vitamin D_15.05.2011.xls (application/vnd.ms-excel)