Screening for microalbuminuria in patients with diabetes mellitus: frozen storage of urine samples decreases their albumin content

The influence of storage on urinary albumin concentration was prospectively studied with use of overnight urine specimens (Albustix negative) from 73 diabetic patients. From each urine sample four aliquots were taken. One was stored at 4 degrees C and assayed within two weeks, the other three were stored at -20 degrees C and assayed within two weeks and after two and six months. Albumin concentration was measured with laser immunonephelometry. The detection limit, 1 mg/L, suffices for the screening of diabetic patients for microalbuminuria. After storage for two and six months at -20 degrees C, significantly lower albumin concentrations were found. The difference was mainly caused by lower concentrations found in urine samples in which a precipitate had formed, which was the case in 22 and 25 samples, respectively. Thus, freezing of urine samples for determination of low concentrations of albumin may yield falsely low results. Urine samples are best stored at 4 degrees C and assayed within two weeks.     

Sample preparation and storage can change arsenic speciation in human urine.

BACKGROUND: Stability of chemical speciation during sample handling and storage is a prerequisite to obtaining reliable results of trace element speciation analysis. There is no comprehensive information on the stability of common arsenic species, such as inorganic arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid, dimethylarsinic acid, and arsenobetaine, in human urine. METHODS: We compared the effects of the following storage conditions on the stability of these arsenic species: temperature (25, 4, and -20 degrees C), storage time (1, 2, 4, and 8 months), and the use of additives (HCl, sodium azide, benzoic acid, benzyltrimethylammonium chloride, and cetylpyridinium chloride). HPLC with both inductively coupled plasma mass spectrometry and hydride generation atomic fluorescence detection techniques were used for the speciation of arsenic. RESULTS: We found that all five of the arsenic species were stable for up to 2 months when urine samples were stored at 4 and -20 degrees C without any additives. For longer period of storage (4 and 8 months), the stability of arsenic species was dependent on urine matrices. Whereas the arsenic speciation in some urine samples was stable for the entire 8 months at both 4 and -20 degrees C, other urine samples stored under identical conditions showed substantial changes in the concentration of As(III), As(V), monomethylarsonic acid, and dimethylarsinic acid. The use of additives did not improve the stability of arsenic speciation in urine. The addition of 0.1 mol/L HCl (final concentration) to urine samples produced relative changes in inorganic As(III) and As(V) concentrations. CONCLUSIONS: Low temperature (4 and -20 degrees C) conditions are suitable for the storage of urine samples for up to 2 months. Untreated samples maintain their concentration of arsenic species, and additives have no particular benefit. Strong acidification is not appropriate for speciation analysis.     

Stability of mycophenolic acid and glucuronide metabolites in human plasma and the impact of deproteinization methodology

BACKGROUND: In recent years there is growing interest in therapeutic drug monitoring of mycophenolic acid (MPA) and its glucuronide metabolites MPAG and AcMPAG. Like other acyl glucuronide metabolites, AcMPAG has a limited stability, but this aspect has received little attention. METHODS: Plasma sample deproteinization with perchloric acid 2 M (method A) was compared to metaphosphoric acid 15% (method B). Stability of MPA, MPAG and AcMPAG in acidified and non-acidified plasma stored at room temperature, 4 degrees C, -20 degrees C and -80 degrees C was assessed over short and long time intervals using HPLC-UV methodology. RESULTS: The area ratio of AcMPAG/IS on spiked plasma at pH 2.5 with method A was 63% of the respective ratio in water, in contrast to 102% with method B, suggesting partial deconjugation and/or incomplete release of AcMPAG from proteins with method A. At room temperature, AcMPAG concentrations in both whole blood and non-acidified plasma decreased significantly after 2-5 h. MPA, MPAG and AcMPAG concentrations remained stable in acidified plasma stored at -20 degrees C and -80 degrees C, but not longer than 5 months after collection. CONCLUSIONS: It is concluded that adequate sample collection, storage measures and deproteinization methods should be applied in order to avoid deconjugation and hence underestimation of MPA, MPAG and AcMPAG concentrations.     

Study of preanalytical conditions for selenium determination in urine.

OBJECTIVE: Assessment of preanalytical and storage conditions for selenium determination in urine. DESIGN AND METHOD: A design is established for the study of the effect of HCl as sample preservative, and for the stability of urine samples with time and temperature of storage. The effect of sample sonication before taking aliquots is also evaluated. All measurements are performed using hydride generation atomic fluorescence spectrometry. Selenium concentrations measured from 52 urine samples of healthy population in Barcelona are used for an estimation of the selenium reference level. RESULTS: HCl addition to urine samples has no effect on Se stability. Significant differences are due to time and temperature of storage. The Se reference level in urine samples from population in Barcelona area is estimated to be 22.8 +/- 6.7 microg Se g(CT)(-1) (CT: creatinine). CONCLUSIONS: No significant differences are observed in selenium content when HCl is added as preservative. The Se content remains constant at room temperature for one day, for a week at 4 degrees C and for a fortnight when stored at -20 degrees C.     

Effects of processing and storage conditions on amyloid beta (1-42) and tau concentrations in cerebrospinal fluid: implications for use in clinical practice

BACKGROUND: Reported concentrations of amyloid beta (1-42) (A beta 42) and tau in cerebrospinal fluid (CSF) differ among reports. We investigated the effects of storage temperature, repeated freeze/thaw cycles, and centrifugation on the concentrations of A beta 42 and tau in CSF. METHODS: Stability of samples stored at -80 degrees C was determined by use of an accelerated stability testing protocol according to the Arrhenius equation. A beta 42 and tau concentrations were measured in CSF samples stored at 4, 18, 37, and -80 degrees C. Relative CSF concentrations (%) of the biomarkers after one freeze/thaw cycle were compared with those after two, three, four, five, and six freeze/thaw cycles. In addition, relative A beta 42 and tau concentrations in samples not centrifuged were compared with samples centrifuged after 1, 4, 48, and 72 h. RESULTS: A beta 42 and tau concentrations were stable in CSF when stored for a long period at -80 degrees C. CSF A beta 42 decreased by 20% during the first 2 days at 4, 18, and 37 degrees C compared with -80 degrees C. CSF tau decreased after storage for 12 days at 37 degrees C. After three freeze/thaw cycles, CSF A beta 42 decreased 20%. CSF tau was stable during six freeze/thaw cycles. Centrifugation did not influence the biomarker concentrations. CONCLUSIONS: Repeated freeze/thaw cycles and storage at 4, 18, and 37 degrees C influence the quantitative result of the A beta 42 test. Preferably, samples should be stored at -80 degrees C immediately after collection.     

Reproducibility and accuracy of measurements of free and total prostate-specific antigen in serum vs plasma after long-term storage at -20 degrees C

BACKGROUND: Long-term frozen storage may alter the results of prostate-specific antigen (PSA) measurements, mainly because of degradation of free PSA (fPSA) in vitro. We compared the effects of long-term storage on fPSA, total PSA (tPSA), and complexed PSA (cPSA) in serum vs EDTA-plasma samples. METHODS: We measured fPSA and tPSA concentrations in matched pairs of archival serum and EDTA-plasma samples (stored frozen at -20 degrees C for 20 years) from a large population-based cohort in Malm?, Sweden. We also compared concentrations in age-matched men with those in samples not subjected to long-term storage, obtained from participants in a population-based study of prostate cancer screening in G?teborg, Sweden. These contemporary samples were handled according to standardized preanalytical and analytical protocols aimed at minimizing in vitro degradation. tPSA and fPSA measurements were performed with a commercial assay (Prostatus Dual Assay; Perkin-Elmer Life Sciences). RESULTS: Concentrations of tPSA and fPSA and calculated cPSA (tPSA - fPSA) in archival plasma were not significantly different from those in contemporary serum from age-matched men. In archival serum, however, random variability of fPSA was higher vs plasma than in contemporary samples, whereas systematic error of fPSA analyses was similarly small in archival and contemporary serum and plasma. CONCLUSIONS: Concentrations of tPSA and calculated cPSA were highly stable in plasma and serum samples subjected to long-term storage at -20 degrees C. Greater random variability, rather than a systematic decrease, may explain differences in fPSA analyses observed in archival serum.     

Storage of buffy coat-derived platelets in additive solutions: in vitro effects of storage at 4 degrees C

BACKGROUND: The aims of this in vitro study were to compare the storage of platelets (PLTs) at 4 degrees C with those stored at 22 degrees C and to determine the in vitro effects of preincubation at 37 degrees C for 1 hour before the analysis on the basis of the maintenance of PLT metabolic and cellular integrity. STUDY DESIGN AND METHODS: PLT concentrates (PCs) were prepared from pooled buffy coats (BCs) for paired studies (total eight pools from 160 BCs). Each pool was divided into four PCs and stored under different conditions: at 20 to 24 degrees C on a flatbed agitator, at 20 to 24 degrees C on a flatbed agitator and with incubation of the samples at 37 degrees C for 1 hour before the analysis, at 4 degrees C, and at 4 degrees C and with incubation of the samples at 37 degrees C for 1 hour before the analysis. RESULTS: Storage of PLTs at 4 degrees C resulted in reductions in the rate of glycolysis and better retention of pH after Day 10 than in PCs stored at 22 degrees C (Day 14, 7.003 +/- 0.047 vs. 7.201 +/- 0.146). Hypotonic shock response and extent of shape change were higher at 22 degrees C than at 4 degrees C and in preincubated PCs stored at 22 degrees C than in reference PCs stored at the same temperature (Day 5, 45.6 +/- 2.7 vs. 36.5 +/- 3.9 and 24.1 +/- 2.0 vs. 15.5 +/- 1.8). The concentration of RANTES was higher in PCs stored at 22 degrees C than at 4 degrees C (Day 7, 179 +/- 25 vs. 79 +/- 32). CONCLUSION: PLTs stored at 4 degrees C without agitation maintain metabolic and cellular characteristics to a great extent during 21 days of storage. These studies confirm the view that PLTs lose their discoid shape and that this loss with storage at 4 degrees C is associated with reductions in metabolic rate and in their release of alpha-granule content.     

Long-term stability of endogenous B-type natriuretic peptide (BNP) and amino terminal proBNP (NT-proBNP) in frozen plasma samples.

The aim of the present study was to assess the long-term stability of endogenous B-type natriuretic peptide (BNP) and amino terminal proBNP (NT-proBNP) in plasma samples stored at -20 degrees C without addition of protease inhibitors (e.g., aprotinin). Stability of BNP and NT-proBNP was tested in 60 EDTA plasma samples with BNP values between 30 and 420 pg/ml. Initial BNP and NT-proBNP plasma concentrations were determined within four hours after blood collection using the AxSYM BNP and the Elecsys NT-proBNP assays. Subsequently, all samples were stored at -20 degrees C and were thawed for the second BNP and NT-proBNP determination on the two instruments after one day, 30 days, 60 days, 90 days and 120 days, respectively. Mean recovery (i.e., residual immunoreactivity) of BNP and NT-proBNP expressed in percent of the initial value for the given time interval of storage was calculated. Mean recovery of BNP was less than 70% after one day of storage at -20 degrees C and decreased to less than 50% after two to four months of storage (e.g., recovery of endogenous BNP after three months of storage at -20 degrees C ranging from 0% to 71%). In contrast, mean recovery of NT-proBNP was generally greater than 90%, irrespective of the duration of storage at -20 degrees C (e.g., recovery of endogenous NT-proBNP after three months of storage at -20 degrees C ranging from 91% to 112%). In conclusion, the determination of endogenous BNP with the AxSYM assay using frozen plasma samples may not be valid under the conditions tested. In contrast, NT-proBNP as measured by the Elecsys assay may be stored at -20 degrees C for at least four months without a relevant loss of the immunoreactive analyte.     

Effects of storage and handling conditions on concentrations of individual carotenoids, retinol, and tocopherol in plasma

We investigated the effects of storage and handling on measured values for carotenoids, retinol, and tocopherol in plasma. We found no significant differences in the concentrations of these analytes measured in plasma samples that were frozen immediately after separation as compared with replicate samples maintained at room temperature in the dark for 24 h. Analytes were stable in solvents for at least 18 h at 23 degrees C after extraction. Purging samples with nitrogen gas before freezing had no detectable beneficial effects. All analytes were stable in plasma stored at -70 degrees C for at least 28 months or at -20 degrees C for five months. By 15 months the concentrations of carotenoids were significantly less (P less than 0.05) in plasma stored at -20 degrees C than in plasma stored at -70 degrees C, while retinol and tocopherol concentrations were not significantly different. Concomitant with the decrease in carotenoids was the appearance of unidentified peaks in the ultraviolet. Adding ascorbic acid or butylated hydroxytoluene antioxidants to the precipitating solvent did not alter the losses of carotenoids or alter the appearance of unidentified peaks. Under appropriate conditions, plasma carotenoids, retinol, and tocopherol are stable for more than two years.     

In vitro stability of the immunoreactivity of the ovarian cancer-associated antigen CA 125

A commercially available two-site solid phase radio-immunoassay was used to study the influence of time and temperature on the in vitro stability of CA 125. In whole blood samples stored at 20 degrees C the CA 125 immunoreactivity increased significantly after 2 days of storage. However, serum could be stored at 20 degrees C for 3 days and at -20 degrees C and -80 degrees C for three weeks without statistically significant changes in the CA 125 immunoreactivity. Therefore, for storage up to 3 days at 20 degrees C, serum should be preferred. For prolonged storage serum samples should be kept at -20 degrees C or -80 degrees C.     

Serum and plasma fragments of C-telopeptides of type I collagen (CTX) are stable during storage at low temperatures for 3 years

BACKGROUND: Control of pre-analytical variables is essential for successful application of biological markers, including bone resorption markers, in clinical trials and routine use. The effect of storage temperature on stability of bone resorption markers have not been subject of systematically investigation, and therefore the present study was set out to determine the stability of C-telopeptides of type I collagen (CTX) in serum and plasma samples stored frozen for 3 years. METHODS: The serum and plasma levels of CTX were determined in samples aliquoted and stored frozen for up to 3 years. RESULTS: No significant decrease could be detected in neither serum nor plasma samples after 3 years of storage at -20, -80 or -150 degrees C. However, at elevated temperature, i.e. 4 and 37 degrees C, improved stability of CTX was observed in EDTA plasma samples compared to serum. CONCLUSIONS: CTX is stable in frozen serum and plasma samples for up to 3 years. EDTA plasma might be the preferred matrix due to improved stability at elevated temperatures.     

Effect of 24-hour whole-blood storageon plasma clotting factors

BACKGROUND: The current requirements for the preparation of fresh-frozen plasma within 8 hours of whole-blood collection were designed to maintain clotting factor activities. These requirements, however, limit the production of fresh-frozen plasma in a large blood center. There are few data on the effect of the extension of CPD whole-blood storage to 24 hours on clotting factor activity. STUDY DESIGN AND METHODS: A 500-mL unit of whole blood was collected from 10 volunteer donors. At 1 hour after collection, a plasma sample was separated by centrifugation, and each unit was equally divided into 2 half-units, with 1 half-unit stored at 4 degrees C (range, 1-6 degrees C) and 1 half-unit stored at 22 degrees C (range, 20-24 degrees C) for 8 hours after collection. Each half-unit was then placed at 4 degrees C for further storage for 16 hours. At 8 and 24 hours after collection, plasma samples were separated from each half-unit. All plasma samples were frozen at -18 degrees C. Factors V, VII, VIII, and X; fibrinogen; antithrombin III; protein C; and protein S were measured. RESULTS: No significant changes were noted in factors V, VII, and X; fibrinogen; antithrombin III; protein C; and protein S over the 24-hour storage period. Factor VIII in both half-units was significantly reduced, by 13 percent, from the baseline sample as compared to the level in the 8-hour storage sample (p<0.05). Factor VIII was further reduced by 15 to 20 percent after the 24-hour storage period (p<0.05). CONCLUSION: The coagulation factor activity for all factors measured, with the exception of factor VIII, showed no significant change over the 24-hour storage period. Factor VIII was significantly decreased by 13 percent in 8-hour storage and by an additional 15 to 20 percent in 24-hour storage. For clinical situations not requiring the replacement of factor VIII only, 24-hour frozen plasma has properties comparable to those of fresh-frozen plasma.     

Long-term stability of salivary cortisol

The measurement of salivary cortisol provides a simple, non-invasive, and stress-free measure frequently used in studies of the hypothalamic-pituitary-adrenal axis activity. In research projects, samples are often required to be stored for longer periods of time either because of the protocol of the project or because of lack of funding for analysis. The aim of the present study was to explore the effects of long-term storage of samples on the amounts of measurable cortisol. Ten pools of saliva were collected on polyester Salivette tampons from five subjects. After centrifugation the samples were either stored in small vials or spiked to polyester Salivette tampons before analysis for cortisol using Spectria RIA kits. The effects of storage were evaluated by a linear regression model (mixed procedure) on a logarithmic scale. No effects on cortisol concentrations were found after storage of saliva at 5 degrees C for up to 3 months or at -20 degrees C and -80 degrees C for up to one year. In contrast, concentrations of cortisol were found to decrease by 9.2% (95% confidence interval (CI): 3.8%; 14.3%) per month in samples stored at room temperature. Repeated freezing and thawing of samples up to four times before analysis did not affect the measured concentrations of cortisol. The coefficient of residual variation (CVresid) for samples stored on Salivette tampons were twice the CVresid for samples stored in separate vials after centrifugation. In conclusion, centrifuged saliva samples for analysis of cortisol may be stored at 5 degrees C for up to 3 months or at -20 degrees C or -80 degrees C for at least one year. However, long-term storage at room temperature cannot be recommended. Repeated cycles of freezing and thawing did not appear to affect the concentrations of cortisol.     

Stability of total plasma homocysteine in perinatology

BACKGROUND: Typical assay methods for total homocysteine in human plasma involve EDTA-containing whole blood. Unfortunately, rapid increases of the plasma homocysteine concentrations due to cellular export are observed when the EDTA-containing samples are not stored on ice and processed shortly after collection. This is a cumbersome procedure in perinatal settings, whereby delivery usually takes place at unpredictable times. METHODS: The stability of homocysteine was assessed from six placental and neonatal blood samples collected in citrate buffer. Samples were stored at 4 degrees C and tested at regular intervals for the first 24 h. RESULTS: There was no statistical difference in homocysteine concentrations as observed over the study storage period (mean coefficient of variation [CV] 4.9%). CONCLUSIONS: Citrated samples can be left in a refrigerator for at least 24 h with no effect on the plasma homocysteine concentrations.     

Effect of anticoagulants and storage temperatures on stability of plasma and serum hormones

OBJECTIVES: To determine the effect of different anticoagulants and storage conditions on the stability of hormones in plasma and serum. DESIGN AND METHODS: Human blood samples were collected from volunteers into EDTA, lithium heparin, sodium fluoride/potassium oxalate, or tubes without anticoagulant, plasma and serum left at -20 degrees C, 4 degrees C or 30 degrees C for 24 and 120 hours then assayed for ACTH, aldosterone, alpha-subunit, AVP, CRH, C-peptide, estradiol, FSH, glucagon, GH, IGF-1, IGFBP-3, insulin, leptin, LH, PPP, PTH, prolactin and VIP, or at room temperature for 0 to 72 hours (BNP, NT-BNP)(n = 6 per condition). RESULTS: The anticoagulant altered the measured concentrations for 9 hormones when compared to EDTA. All hormones except ACTH were stable for > 120 hours in EDTA or fluoride at 4 degrees C, but only 13 hormones were stable in all anticoagulants. At 30 degrees C, 8 hormones were stable for > 120 hours in EDTA, and 3 hormones in all anticoagulants. BNP and NT-BNP were stable for < 24 hours when stored in EDTA or heparin at room temperature. DISCUSSION: Storage of samples in EDTA plasma at 4 degrees C is suitable for most hormones (except ACTH) for up to 120 hours.     

Determination of ascorbic acid in plasma and urine by high performance liquid chromatography with ultraviolet detection.

A reliable simple reversed-phase liquid chromatographic method for the routine determination of ascorbic acid in plasma and urine with ultraviolet detection is described. This method enables the complete separation of the ascorbic acid peak from others with a recovery of above 95% within 8 minutes. The method can be used for analysing multiple samples within a day. In addition, the storage conditions and stability of ascorbic acid in plasma and urine were investigated. Samples of plasma and urine can be stored on ice in darkness for at least 60 min without reduction of ascorbic acid concentration. Prepared samples can be stored in darkness at 4 degrees C for at least 120 min and in liquid nitrogen for 42 days.     

Clinical pharmacokinetics of lorazepam. II. Intramuscular injection.

A single dose of 4 mg of lorazepam was injected into the deltoid muscles of six healthy male volunteers. Multiple venous blood samples were drawn during 48 hr after the dose and all urine was collected for 24 hr after the dose. Concentrations of lorazepam and its major metabolite, lorazepam glucuronide, were determined by electron-capture gas-liquid chromatography. Lorazepam was rapidly absorbed from the injection site, reaching peak concentrations within 3 hr. Mean pharmacokinetic pamrameters for unchanged lorazepam were: apparent absorption half-life: 21.2 min; elimination half-life: 13.6 hr; volume of distribution: 0.9 L/kg; total clearance: 58.2 ml/min. Lorazepam glucuronide rapidly appeared in plasma, reached peak concentrations within 12 hr of the dose, then was eliminated approximately in parallel with the parent drug. Within 24 hr a mean of 47.6% of the dose was recovered in the urine as lorazepam glucuronide and less than 0.5% was recovered as unchanged lorazepam.     

Apparent loss of urinary albumin during long-term frozen storage: HPLC vs immunonephelometry

BACKGROUND: Urinary albumin detection by immunonephelometry is decreased by approximately 30% in samples that have been frozen at -20 degrees C. An HPLC method for assessment of urinary albumin that detects immunoreactive and immunochemically nonreactive albumin has been introduced as an alternative to immunonephelometry. We investigated whether this technique is affected by sample temperature, particularly freezing. METHODS: Urine samples (n = 295) were collected from the general population (Prevention of Renal and Vascular End-Stage Disease Study). Samples were assessed by both immunonephelometry and HPLC when fresh and after storage at -20 degrees C for 4, 8, and 12 months and at -80 degrees C for 12 months. RESULTS: With immunonephelometry, storage for 4, 8, and 12 months at -20 degrees C resulted in mean (SD) urine albumin changes of -21% (29%), -28% (29%), and -34% (31) (P <0.001 for trend). Storage at -80 degrees C resulted in a 5% (19%) change after 12 months of storage (not significant). With HPLC, storage for 4, 8, and 12 months at -20 degrees C resulted in urine albumin changes of -33% (28%), -43% (24%), and -55% (21%; P <0.001 vs immunonephelometry). Storage at -80 degrees C resulted in a -29% (29%) change (P <0.001 vs immunonephelometry). CONCLUSION: Loss of albumin after freezing urine depends not only on freezing temperature but also on detection method. Detection of albumin by immunonephelometry appears to be significantly less influenced by freezing than detection by HPLC. Storage at -80 degrees C appears to prevent loss when using immunonephelometry, whereas HPLC still shows considerable loss even when urine is frozen at -80 degrees C. We propose that for reliable measurement of urine albumin, fresh samples should be used.     

不同处理和保存条件下体外HCV RNA稳定性研究

对献血者或病人进行HCV核酸检测时，如果标本的采集、处理、保存不当，会造成病毒核酸降解，从而影响检测结果的真实性。本研究的目的是对不同抗凝剂、不同温度、不同保存时间下的HCV RNA病毒稳定性进行研究，以考察常规采供血过程中，标本采集及保存方式对NAT检测的影响。采集7例HCV RNA阳性献血者的血样，采用不同的抗凝剂、经不同的温度和不同的时间保存后，采用荧光定量PCR方法测定HCV RNA病毒含量，考察HCV RNA的稳定性。结果表明：①不同抗凝剂抗凝的全血于4℃保存48小时过程中，病毒含量下降至原滴度的42．7％；EDTA抗凝组各时间点的滴度均低于其它3组（分别相当于其它3组的67．6％-25．1％）。②ACD抗凝的全血在4、25和37℃保存48小时．病毒含量分剐下降到原滴度的53．8％、72．5％、29．8％。③ACD抗凝的全血离心分离出血浆，4℃或25℃继续保存7天，病毒含量分别下降至原滴度的70．9％和25．1％。④ACD抗凝的全血分离的血浆，反复冻融4次，病毒含量下降到原滴度的38．9％。结论：①用于核酸检测的标本应该用无菌采血管采样；②在无菌采血管采样的前提下，核酸检测标本用未抗凝血、EDTA、ACD、CPDA抗凝血均可；③采集的全血应避免放置37℃以上，ACD抗凝全血在4℃、25℃保存48小时内、37℃保存14小时内，HCV RNA病毒仍较为稳定；④分离后的血浆应避免放置25℃以上，ACD抗凝全血分离后的血浆在4℃保存7天，25℃保存3天，HCV RNA病毒仍比较稳定；⑤血浆标本应避免多次冻融，但冻融3次的血浆HCV RNA病毒含量仍然较为稳定；⑥无菌采样对维持病毒的稳定性非常重要；单纯的机械性溶血并不会明显导致病毒的降解；只要注意无菌的问题和有合适的核酸提取方法去除血红素，HCV RNA病毒实际上比以前认为的要稳定得多。     

Stability of serum fructosamine during storage

Stability of serum fructosamine during storage was evaluated in serum specimens obtained from 27 diabetic individuals. The samples were divided into six aliquots, which were stored at -20 degrees C and -70 degrees C for two, eight, and 16 months. The minor systematic differences between the six treatments contrasted with the considerable variation of individual specimens. The mean percentage changes in the six treatments ranged between -4.6% and 7.5%, whereas the changes in individual specimens ranged from -20% to 26.7%. Several factors evidently contribute to this variation, one being progressive in vitro glycation, especially at -20 degrees C. Small changes in fructosamine concentrations between consecutively drawn specimens, determined after storage, evidently should be interpreted cautiously. Low temperatures, at least -70 degrees C, are preferable to minimize pre-analytical variation during storage.