Acute fluid shifts influence the assessment of serum vitamin D status in critically ill patients.
BACKGROUND
Recent reports have highlighted the prevalence of vitamin D deficiency and suggested an association with excess mortality in critically ill patients. Serum vitamin D concentrations in these studies were measured following resuscitation. It is unclear whether aggressive fluid resuscitation independently influences serum vitamin D.


METHODS
Nineteen patients undergoing cardiopulmonary bypass were studied. Serum 25(OH)D(3), 1α,25(OH)(2)D(3), parathyroid hormone, C-reactive protein (CRP), and ionised calcium were measured at five defined timepoints: T1 - baseline, T2 - 5 minutes after onset of cardiopulmonary bypass (CPB) (time of maximal fluid effect), T3 - on return to the intensive care unit, T4 - 24 hrs after surgery and T5 - 5 days after surgery. Linear mixed models were used to compare measures at T2-T5 with baseline measures.


RESULTS
Acute fluid loading resulted in a 35% reduction in 25(OH)D(3) (59 ± 16 to 38 ± 14 nmol/L, P < 0.0001) and a 45% reduction in 1α,25(OH)(2)D(3) (99 ± 40 to 54 ± 22 pmol/L P < 0.0001) and i(Ca) (P < 0.01), with elevation in parathyroid hormone (P < 0.0001). Serum 25(OH)D(3) returned to baseline only at T5 while 1α,25(OH)(2)D(3) demonstrated an overshoot above baseline at T5 (P < 0.0001). There was a delayed rise in CRP at T4 and T5; this was not associated with a reduction in vitamin D levels at these time points.


CONCLUSIONS
Hemodilution significantly lowers serum 25(OH)D(3) and 1α,25(OH)(2)D(3), which may take up to 24 hours to resolve. Moreover, delayed overshoot of 1α,25(OH)(2)D(3) needs consideration. We urge caution in interpreting serum vitamin D in critically ill patients in the context of major resuscitation, and would advocate repeating the measurement once the effects of the resuscitation have abated.
Intensive Care Unit, Princess Alexandra Hospital, University of Queensland, Ipswich Road, Woolloongabba, QLD 4102, Australia.
Anand
A
Krishnan
Judith
J
Ochola
Julie
J
Mundy
Mark
M
Jones
Peter
P
Kruger
Emma
E
Duncan
Bala
B
Venkatesh
D000208:Acute Disease; D000368:Aged; D015415:Biomarkers / Q000097:blood; D016638:Critical Illness; D005260:Female; D018495:Fluid Shifts / Q000502:physiology*; D006438:Hemodilution / Q000009:adverse effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D013997:Time Factors; D014807:Vitamin D / Q000097:blood*; D014808:Vitamin D Deficiency / Q000097:blood* / Q000209:etiology
D015415:Biomarkers; D014807:Vitamin D