Chromatography of serum on Sep-pak C18 corrects falsely elevated vitamin D metabolite levels measured by protein binding assay.
Using a commercial kit method we obtained a vitamin D metabolite level within the normal range in a patient with biopsy-proven osteomalacia. This suggested that the ethanol extraction method employed had not removed serum factors known to falsely elevate the measurement of vitamin D metabolites. We therefore compared the levels measured after ethanol extraction and after purification by chromatography on Sep-pak C18 or Sephadex LH-20. Vitamin D metabolite levels after ethanol extraction of sera correlated with, but were higher than, those after chromatography on Sep-pak C18 cartridges (r = 0.84; 134 +/- 76 vs 76 +/- 46 nmol/l: mean +/- SD; p less than 0.01). Results were similar after chromatography on Sep-pak C18 and Sephadex LH-20 (r = 0.95; 79 +/- 46 vs 68 +/- 41 nmol/l). Sera from 5 patients (4 with osteomalacia, 1 with chronic pancreatitis/malabsorption) had vitamin D metabolite levels in the normal range after ethanol extraction but had low levels after Sep-pak C18 chromatography; four of these sera also had low levels after chromatography on Sephadex LH-20. These findings indicate that chromatography of serum on Sep-pak C18 cartridges corrects falsely elevated vitamin D metabolite levels measured by protein binding assay.
Dean
B
B
Endocrine Laboratory, Royal Melbourne Hospital, Parkville, Victoria, Australia.
Kolavcic
M S
MS
Wark
J D
JD
Harrison
L C
LC
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002850:Chromatography, Gel / Q000379:methods; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011485:Protein Binding; D011933:Reagent Kits, Diagnostic; D012016:Reference Values; D012822:Silicon Dioxide; D014807:Vitamin D / Q000097:blood*
D011933:Reagent Kits, Diagnostic; D014807:Vitamin D; D012822:Silicon Dioxide; C042953:octadecyl silane-bonded silica