Rw. Evans et al., EFFECT OF SAMPLE STORAGE ON QUANTITATION OF LIPOPROTEIN(A) BY AN ENZYME-LINKED-IMMUNOSORBENT-ASSAY, Lipids, 31(11), 1996, pp. 1197-1203
This study evaluated the effect of storage on the quantitation of lipo
protein (Lp)(a) in 25 serum samples. Aliquots of serum were stored for
up to three years at either -20 degrees C or -70 degrees C and Lp(a)
subsequently analysed using an enzyme-linked immunosorbent assay kit.
Concentrations of Lp(a) declined during storage, and the temperatures
employed elicited significantly different (P < 0.05) values within 12
mon which further diverged during three years of storage. Compared to
baseline values, significant decreases (P < 0.05) in Lp(a) levels were
evident after six months of storage at -20 degrees C with apparent lo
sses (geometric mean) reaching 36.9% (95% confidence interval: 30.9%,
42.9%) after three years. Similarly, significantly lower (P < 0.05) Lp
(a) values were recorded after six months of storage at -70 degrees C
and at three years the decrease (geo-metric mean) was 19.1% (95% confi
dence interval: 14.3%, 24.0%). The losses, after three years, in terms
of the arithmetic mean were 53.5 and 26.2% at -20 and -70 degrees C,
respectively. Phenotype analysis suggested that large isoforms are mor
e susceptible to degradation than smaller moieties. This may be relate
d to the observation that apparent losses are reduced in samples conta
ining over 8 mg/dL Lp(a). Nevertheless, Lp(ai levels in stored samples
retained a strong correlation with the baseline values. These results
must be considered specific for the storage conditions and analytical
procedures employed.