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BackgroundProficiency testing (PT) has been hard to set up due to cost limitations and technical capacity. Conventional Xpert MTB/RIF PT programs use liquid and culture spots which require stringent storage and transportation conditions with cross-contamination chances prevalent. These setbacks prompted the use of dried tube specimens (DTS) for Ultra assay PT. For continuity of PT provision, stability of DTS and compatibility with testing protocols when kept for a long period needs to be established.MethodsDTS were prepared from known isolates inactivated using a hot air oven at 85°C. 100μl of bacterial suspensions were aliquoted and dried inside a Biosafety cabinet. Panel validation was done to establish the baseline Deoxyribonucleic acid (DNA) concentration in terms of cycle threshold (Ct) value. DTS aliquots were shipped to participants to test and report within six weeks. The remaining DTS were kept at 2–8°C and room temperature for one year with testing at six months. Twenty (20) DTS samples per set remaining at one year were heated at 55°C for two weeks before testing. The means of the different samples were compared to validation data using paired t-tests. Boxplots were designed to visualize the differences in the medians of the DTS.ResultsOverall mean Ct value increased by 4.4 from the validation to testing after one year at the different storage conditions. Samples heated at 55°C showed a 6.4 Ct difference from validation data. Testing done at six months on 2–8°C stored items showed no statistical difference. At all the remaining testing times and conditions, P-values were less than 0.008 although the absolute mean Ct when compared showed slight increments and accommodated differences for the detection of MTB and rifampicin resistance. Median values for samples stored at 2–8°C were lower compared to those at room temperature.ConclusionDTS stored at 2–8°C remain more stable for one year compared to higher temperatures and can be consistently used as PT materials in more than one PT round for biannual PT providers.

背景
由于成本限制与技术能力不足，能力验证（Proficiency testing, PT）的搭建一直存在难度。传统Xpert MTB/RIF检测系统的能力验证项目采用液态标本与培养斑片，这类标本对储存与运输条件要求严苛，且极易发生交叉污染。上述缺陷推动了干管标本（dried tube specimens, DTS）在Ultra检测试剂盒能力验证中的应用。为保障能力验证服务的持续性供给，需明确干管标本的长期储存稳定性及其与检测流程的兼容性。

方法
以经85℃热风烘箱灭活的已知菌株为材料制备干管标本。取100μl菌悬液分装后，置于生物安全柜内进行干燥处理。通过验证组实验确定以循环阈值（cycle threshold, Ct）值为指标的脱氧核糖核酸（Deoxyribonucleic acid, DNA）基线浓度。将分装的干管标本寄送至参与机构，要求其在六周内完成检测并反馈结果。将剩余干管标本分别置于2~8℃与室温环境储存一年，并于储存六个月时开展一次检测。储存满一年的各组剩余标本中，各取20份干管标本置于55℃加热两周后再进行检测。采用配对t检验将不同样本的均值与验证数据进行对比，并通过箱线图直观展示干管标本中位数的差异。

结果
不同储存条件下，储存一年后检测的整体平均Ct值较验证实验时升高了4.4。经55℃加热处理的标本，其Ct值与验证数据的差值达6.4。对2~8℃储存的标本在六个月时开展的检测结果显示，其与验证数据无统计学差异。其余所有检测时间与储存条件下，P值均小于0.008；尽管相较验证数据的绝对平均Ct值存在小幅升高，但仍可满足结核分枝杆菌（Mycobacterium tuberculosis, MTB）与利福平（rifampicin）耐药性检测的差异判别要求。2~8℃储存的标本中位数Ct值低于室温储存的标本。

结论
相较于更高温度储存条件，2~8℃储存的干管标本在一年内稳定性更佳，可作为能力验证材料重复用于多轮能力验证，适用于每半年开展一次能力验证的服务机构。