確保檢驗正確性－－總膽紅素應於採檢後八小時內完成檢驗

For Accurate Measurement of Total Bilirubin Level The Sample Should Be Assayed Within 8 Hours

膽紅素因化學結構特性，受光照射後濃度會下降。臨床檢驗室因醫療需求，經常以現有檢體補驗總膽紅素，為避免光照對檢驗結果的影響，各檢驗室皆有補驗的時間規範，但無一致的標準。本研究目的乃探討檢體受光照射時間與總膽紅素濃度變化的相關性及分析光照時間對不同膽紅素濃度的影響，進一步訂定檢體可容許光照時間以供依循。我們收集30支血清檢體，先測量總膽紅素濃度，依不同臨床意義設計三組不同濃度之實驗組，在環境溫度20-25℃，以350 Lux照射，以Beckman Coulter Unicel DXC 800生化分析儀，檢測原理為Jendrassik-Grof法，每隔4小時檢測一次總膽紅素濃度，連續觀察72小時。結果顯示這三組光照前總膽紅素濃度平均值分別為1.61mg/dL、6.43 mg/dL、17.52 mg/dL，光照後每4小時濃度下降值分別為0.06 mg/dL、0.07 mg/dL、0.15 mg/dL；下降率分別為3.8%、1.1%、0.9%。在符合照光前後濃度差異小於0.2 mg/dL或小於10%的條件下，這三組可容許光照之時間分別為8小時、36小時及44小時。考量作業規範一致性，檢測總膽紅素濃度之檢體應限制光照時間不可大於8小時，當超過8小時，且屬不易取得之檢體，可利用研究所得之每4小時濃度下降率估算原始濃度。本研究確認檢體光照對總膽紅素之影響，研究結果可提供其他臨床檢驗單位參考，針對補驗總膽紅素檢體，訂立正確的收件標準，減少重覆採檢，提升醫療服務品質。

The bilirubin level will decrease after exposure to light due to the chemical structure. For medical usefulness, clinical laboratories often use specimens to subjoin test of serum total bilirubin (STB). Laboratories have established standards of time limits of light exposure before specimens are analyzed in order to avoid pseudo-low level STB, but the criteria are inconsistent. The purpose of this study was to evaluate the correlation between the exposure time to room light with the changes in STB level. According to these outcomes, we developed criteria for serum exposure time. 30 serum samples were collected from patients who had measured STB levels and then divided into 3 groups by different clinical significance. All samples were exposed to room light at the level of 350 Lux for a total time length of 72 hours in ambient temperature 20-25℃. Every 4 hours, all samples were determined by Diazo-Caffeine/Benzoate Coupline method and analyzed with Beckman Coulter UniCel DXC800 analyzer. Before exposure to light, the average concentrations of STB of the 3 groups are 1.61 mg/dL, 6.43 mg/dL, 17.52 mg/dL, respectively. After exposure to light, average rate of decline per 4 hours are 3.8%, 1.1% and 0.9%, respectively. The extreme limits for serum exposure time are 8 hours, 36 hours and 44 hours, respectively, and the changes in STB level met the laboratory's criteria (Bias＜0.2 mg/ dL or 10%) for acceptable performance. Consider the consistency of standard operations and accurate measurement, the exposure time of specimens to room light should be limited to less than 8 hours. When encountering difficulty redrawing the sample, the average rate of decline in our study could be applied for STB level estimation. In this study, we have confirmed the correlation between exposure time and the changes in STB level, this finding could be reference for developing standard operations process that could reduce the frequency of redrawing samples to improve the quality of medical care.