Bartali et al used age and serum vitamin E concentrations to predict physical decline in a community-dwelling elderly adult. The authors are from Cornell University, Yale University, University of South Carolina, University of Perugia, Azienda Sanitaria Firenze (Florence) and the National Institute of Aging.
Method of analysis: CART (classification and regression tree)
Measure of physical function: Short Physical Performance Battery (4 meter walking speed, repeated chair rises, standing balance from Guralnik et al in Chapter 37) with values ranging from 0 to 12
Patient selection: >= 65 years of age with excellent to poor functional status. A patient with very poor functional status was excluded since there was little to be lost.
Definition of functional decline: loss of >= 1 point in the performance battery over 3 years
Parameters:
(1) age in years
(2) serum vitamin E in µmol/L
Age
Serum Vitamin E
Percent of Patients Showing Decline
65 to 69.44
NA
31%
69.45 to 81
<= 1.38 µg/mL
60%
69.45 to 81
> 1.38 µg/mL
42%
> 81
NA
84%
where:
• 164 days is approximately 0.45 years
• Figure 2 on page 313 reports vitamin E in µg/dL. The text on the same page refers to µg/mL with 1.38 µg/mL = 32 µmol/L. According to Tietz's Clinical Guide to Laboratory Tests the conversion factor for mg/dL to µmol/L is times 23.22 (or mg/L to µmol/L is 2.322). 1.38 µg/dL is about 0.03 µmol/L which is extremely low. 1.38 µg/mL is 3.22 µmol/L which is low but reasonable; however, this is 10% of the value given in the text.
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