Effect of sample storage on quantitation of lipoprotein (a) by an enzyme‐linked immunosorbent assay

Abstract

This study evaluated the effect of storage on the quantitation of lipoprotein (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 analyzed 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 losses (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 (geometric mean) was 19.1% (95% confidence 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 more susceptible to degradation than smaller moieties. This may be related to the observation that apparent losses are reduced in samples containing over 8 mg/dL Lp(a). Nevertheless, Lp(a) 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.

Different Effects of Continuous and Intermittent Patterns of Growth Hormone Administration on Lipoprotein Levels inGrowth Hormone-Deficient Patients

“…Reductions in Lp(a) levels of 7 and 13% have been reported after 24 months storage at –80 and –20°C, respectively [36]. Another study reported losses in Lp(a) of 37 and 19% after storage at –20 and –70°C, respectively, for 3 years [38]. In the present studies samples were stored at –30°C for 1.5–3 years (study A) and 0.5–1.5 years (study B).…”

Design Options for Molecular Epidemiology Research within Cohort Studies

“…Storageinduced changes in biomarker levels can be substantial. Evans et al (35) have reported a 19% decrease in lipoprotein A in serum samples stored for 3 years at À70jC. Additionally, Bolelli et al (40) reported a 30% increase in serum-free testosterone and a 40% decrease in progesterone in samples stored at À80jC for 3 years.…”

“…Benzo(a)pyrene-DNA adducts have been reported to be stable in samples stored for 10 months (34). However, levels of other markers, such as lipoprotein A, total and high-density lipoprotein cholesterol, triglycerides (35)(36)(37), HIV p24 antigen (38), free prostate-specific antigen (39), progesterone (40), estradiol (41), hepatitis virus C RNA concentrations (42), and salivary IgA (43), have been shown to change during sample storage. Additionally, for paraffin-embedded tissue sections, the reliability of immunohistochemical and fluorescence in situ hybridization assays for HER2 decline with storage time (44), as does antigenicity for tissue microarrays (45).…”

“…At a minimum, controls are matched to cases on length of follow-up since entry into the cohort study. In a case-control study nested in the Physicians Health Study, controls were additionally matched to cases on age, smoking status (never, ex, current), cigarettes per day in current smokers (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39), and 40+ cigarettes per day), and analytic batch (4). In Genair/EPIC, a case-control study of noncurrent smokers nested in EPIC, controls were matched to cases on age, gender, country, smoking status (never, ex-smoker), and analytic batch (72).…”

Adiponectin: Stability in Plasma over 36 Hours and Within-Person Variation over 1 Year

“…In addition, the stability of a valid biological marker should not be substantially affected by length of storage or temperature (21)(22)(23)(24)(25). Ideally, serum or plasma from whole blood should be separated immediately and stored in deep freeze.…”