A 44-year-old woman presented with abdominal pain and oliguria 4 days after undergoing total abdominal hysterectomy and right oophorectomy due to uterine myoma and ovarian chocolate cysts. Laboratory findings showed that blood urea nitrogen (BUN) and serum creatinine (Scr) were elevated to 38.7 and 3.75 mg/dL, respectively, whereas preoperative Scr had been within the normal range (0.44 mg/ dL). The patient had no medical history and was not currently on medication. Her physical findings were blood pressure 109/88 mmHg, heart rate 118 beats/min and temperature 36.7 C. Her lower abdomen was slightly hard with rebound tenderness. Laboratory findings (Table 1) showed that serum cystatin C was 0.63 mg/L (normal), in the setting of elevated BUN and Scr. Abdominal computed tomography showed moderate ascites and free air in the abdominal cavity. Levels of urea nitrogen and creatinine in ascites after paracentesis were 92.3 and 13.7 mg/dL, respectively. Both values were higher than those of BUN and Scr (38.7 and 3.75 mg/dL, respectively). Therefore, we diagnosed intraperitoneal urine leakage, because an ascites-Scr ratio >1.0 indicates creatinine reabsorption across the peritoneal membrane. Cystoscopy revealed micro perforation at the posterior bladder wall. Bladder catheterization to reduce intrabladder pressure and obtain urine output reduced BUN and Scr to normal values of 7.0 and 0.52 mg/dL, respectively. Intraperitoneal urine leakage resulted in BUN and Scr elevation through urea nitrogen and creatinine reabsorption across the peritoneal membrane. This unique mechanism is referred to as ‘pseudo-azotaemia’, since glomerular filtration is preserved. Our patient notably had a normal serum cystatin C value, indicating that glomerular filtration was indeed preserved. Although the mechanism of the discrepancy between BUN and Scr and serum cystatin C in pseudoazotaemia remains unclear, it might be associated with molecular weight. The molecular weight of cystatin C is quite large (13 200 Da) and similar to that of β2microglobulin (11 800 Da), indicating that it cannot be easily reabsorbed across the peritoneal membrane. Consequently, serum cystatin C is not elevated in pseudoazotaemia, unlike BUN and Scr. Measuring serum cystatin C is less invasive than measuring urea nitrogen and creatinine by paracentesis. Clinicians should measure serum cystatin C when intraperitoneal urine leakage is suspected.

中文翻译：

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无血清胱抑素 C 升高的急性氮质血症

一名 44 岁女性因子宫肌瘤和卵巢巧克力囊肿接受全腹子宫切除术和右侧卵巢切除术 4 天后出现腹痛和少尿。实验室检查结果显示血尿素氮（BUN）和血清肌酐（Scr）分别升高至 38.7 和 3.75 mg/dL，而术前 Scr 一直在正常范围内（0.44 mg/dL）。患者没有病史，目前没有服药。体格检查结果为血压109/88 mmHg，心率118次/分，体温36.7℃，小腹稍硬，有反跳痛。实验室检查结果（表 1）显示，在 BUN 和 Scr 升高的情况下，血清胱抑素 C 为 0.63 mg/L（正常）。腹部计算机断层扫描显示腹腔内有中度腹水和游离空气。腹腔穿刺后腹水中的尿素氮和肌酐水平分别为 92.3 和 13.7 mg/dL。这两个值都高于 BUN 和 Scr（分别为 38.7 和 3.75 mg/dL）。因此，我们诊断为腹膜内漏尿，因为腹水-Scr 比值 >1.0 表明肌酐重吸收穿过腹膜。膀胱镜检查显示膀胱后壁有微穿孔。用于降低膀胱内压力和获得尿量的膀胱导管插入术将 BUN 和 Scr 分别降至 7.0 和 0.52 mg/dL 的正常值。腹腔漏尿导致尿素氮和肌酐重吸收穿过腹膜导致 BUN 和 Scr 升高。这种独特的机制被称为“假性氮质血症”，因为肾小球滤过功能得以保留。本例患者的血清胱抑素 C 值明显正常，表明确实保留了肾小球滤过。虽然假氮质血症中 BUN 和 Scr 与血清胱抑素 C 之间差异的机制尚不清楚，但可能与分子量有关。胱抑素C的分子量相当大（13 200 Da），与β2微球蛋白（11 800 Da）相似，表明它不易被腹膜重吸收。因此，与 BUN 和 Scr 不同，假氮质血症中血清胱抑素 C 不会升高。与通过穿刺术测量尿素氮和肌酐相比，测量血清胱抑素 C 的侵入性更小。当怀疑腹腔漏尿时，临床医生应测量血清胱抑素 C。虽然假氮质血症中 BUN 和 Scr 与血清胱抑素 C 之间差异的机制尚不清楚，但可能与分子量有关。胱抑素C的分子量相当大（13 200 Da），与β2微球蛋白（11 800 Da）相似，表明它不易被腹膜重吸收。因此，与 BUN 和 Scr 不同，假氮质血症中血清胱抑素 C 不会升高。与通过穿刺术测量尿素氮和肌酐相比，测量血清胱抑素 C 的侵入性更小。当怀疑腹腔漏尿时，临床医生应测量血清胱抑素 C。虽然假氮质血症中 BUN 和 Scr 与血清胱抑素 C 之间差异的机制尚不清楚，但可能与分子量有关。胱抑素C的分子量相当大（13 200 Da），与β2微球蛋白（11 800 Da）相似，表明它不易被腹膜重吸收。因此，与 BUN 和 Scr 不同，假氮质血症中血清胱抑素 C 不会升高。与通过穿刺术测量尿素氮和肌酐相比，测量血清胱抑素 C 的侵入性更小。当怀疑腹腔漏尿时，临床医生应测量血清胱抑素 C。胱抑素C的分子量相当大（13 200 Da），与β2微球蛋白（11 800 Da）相似，表明它不易被腹膜重吸收。因此，与 BUN 和 Scr 不同，假氮质血症中血清胱抑素 C 不会升高。与通过穿刺术测量尿素氮和肌酐相比，测量血清胱抑素 C 的侵入性更小。当怀疑腹腔漏尿时，临床医生应测量血清胱抑素 C。胱抑素C的分子量相当大（13 200 Da），与β2微球蛋白（11 800 Da）相似，表明它不易被腹膜重吸收。因此，与 BUN 和 Scr 不同，假氮质血症中血清胱抑素 C 不会升高。与通过穿刺术测量尿素氮和肌酐相比，测量血清胱抑素 C 的侵入性更小。当怀疑腹腔漏尿时，临床医生应测量血清胱抑素 C。