The Long Haul: Analyte Stability in Archival Serum Samples

The scientific value of biospecimens is a product of sample quality, the degree to which a stored specimen mirrors its biological state at the time of sampling. Major threats to sample quality include degradation and sublimation during storage as well as improper pre-analytical handling. Specimens destined for long-term storage require particular care, including meticulous documentation. Unfortunately, clear longitudinal data on serum analyte stability is often lacking or even contradictory within the literature. This means that studies involving archival serum samples could be flawed by the assumption that changes that occurred during storage were insignificant.

Using serum samples stored at -25ºC for up to 29 years at the Janus Serum Bank, which provides epidemiological study specimens for the Norwegian Cancer Registry, Gislefoss et at.¹ evaluated the long-term stability of selected samples of the following:

Lipids: total cholesterol, HDL cholesterol (HDLC) and LDL cholesterol (LDLC)
Proteins: apolipoprotein A1 (apo-A1) and apolipoprotein B (apo-B)
Hormones: follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), thyroid-stimulating hormone (TSH) and free thyroxine (FT4)

The team found significant differences in serum levels for lipids and lipoproteins, with the exception of total cholesterol.

Median Serum Levels (25 and 75 percentiles)

	0 years storage	4 years storage	17 years storage	29 years storage	Change
Cholesterol (mmol/L)	5.3 (4.6–6.1)	5.2 (4.6–5.8)	5.5 (4.9–6.5)	5.6 (4.9–6.4)	not significant
HDLC (mmol/L)	1.14 (0.90–1.31)	0.74 (0.60–0.89)	0.41 (0.31–0.52)	0.35 (0.27–0.43)	-69.2%
LDLC (mmol/L)	3.10 (2.4–3.8)	2.9 (2.4–3.7)	3.7 (3.0–4.7)	4.0 (3.3–4.7)	+31.3%
Apo-A1 (g/L)	1.55 (1.39–1.72)	1.66 (1.55–1.83)	1.62 (1.47–1.83)	1.71 (1.55–1.90)	+12%
Apo-B (g/L)	0.80 (0.65–0.94)	0.82 (0.69–0.99)	0.99 (0.83–1.26)	0.97 (0.82–1.17)	+22.3%

The majority of the investigated hormones (FSH, LH, TSH and FT4) were relatively stable even after long-term storage. The exception (PRL) demonstrated degradation after only four years.

Median Serum Levels (25 and 75 percentiles)

	0 years storage	4 years storage	17 years storage	29 years storage	Change
FSH (IU/L)	4.1 (3.2–5.8)	4.2 (3.0–6.2)	4.2 (3.3–5.7)	4.2 (3.1–5.8)	not significant
LH (IU/L)	4.4 (3.6–5.8	4.2 (3.3–5.0)	4.3 (3.1–5.6)	4.7 (3.3–6.0)	not significant
TSH (mU/L)	1.6 (1.2–2.1)	1.6 (1.2–2.2)	1.4 (1.0–1.9)	1.5 (1.0–1.9)	not significant
FT4 (pmol/L)	15.2 (14.2–16.6)	16.7 (15.4–17.8)	16.9 (15.4–18.0)	16.2 (14.7–17.4)	not significant
PRL (μIU/L)	163 (125–219)	143 (111–188)	118 (93–162)	109 (90–140)	-33.5%

Gislefoss et al. observed that the serum level changes reported in this study likely derived from a combination of long-term storage effects and external factors, including diet and smoking status. Since the biospecimens used here were largely archival, population-based lifestyle changes—such as lower-fat diets and decreased smoking—could be responsible for some degree of drift, particularly in lipid and lipoprotein measures. Nevertheless, these findings could assist biobankers and researchers in estimating stability data in order to improve the accuracy of studies involving archival biospecimens.

Reference

1. Gislefoss, R. E. et al. (2014) “Stability of selected serum hormones and lipids after long-term storage in the Janus Serum Bank,” Clinical Biochemistry.