C反应蛋白的糊涂账

国内外大部分医院的C反应蛋白 (CRP) 正常值范围都是0-10mg/L，那C反应蛋白高于10是不是就意味着细菌感染，就该用抗生素？

我们先看看这篇研究，有人给普通感冒和流感病人检查C反应蛋白，这些人并没有合并细菌感染，结果如下：

上图可见：普通感冒的人，CRP十几的很多，二三十的也有。而流感呢，二三十的有，超过四十的也有。


更有人归纳了多个前人的研究：大多数的病毒感染，CRP都会轻中度地升高到20~40mg/L，有些病毒感染，例如腺病毒，流感，麻疹，腮腺炎和水痘，更是可以高达100ml/L。

In fact, previous studies have shown that most viral infections are associated with a modest CRP elevation of about 20 to 40 mg/L, although greater elevations of more than 100 mg/L may occur in infections caused by adenovirus, influenza, measles, mumps, and varicella.  What's new in Emergencies Trauma and Shock? C-reactive protein as a potential clinical biomarker for influenza infection: More questions than answers.J Emerg Trauma Shock. 2012 Apr-Jun; 5(2): 115–117

另外一个研究，得出这样的结论：

病毒感染和轻度炎症可引起CRP的轻度升高(10–40 mg/L)，而细菌感染和一些活动性炎症则可使CRP显著升高到40–200 mg/L，一些严重的细菌感染和烧伤可致CRP升高到200以上。

As mentioned, viral infections and any mild inflammation elicit a smaller increase in CRP level (10–40 mg/L), while bacterial infection as well as active inflammation can elicit much higher responses of between 40–200 mg/L. In some severe bacterial infections and burns, the level can increase more than 200 mg/L. The C-reactive protein. J Emerg Med. 1999;17:1019–25

儿童肺炎有人也做过研究，分析了1230例肺炎，其中41%的是细菌性肺炎。结果是细菌性比起病毒性肺炎的孩子，CRP更有可能超过35-60mg/L 。结论是：儿童肺炎，血清CRP超过40-60mg/L可弱弱地预测细菌感染。

Eight studies fulfilled inclusion criteria. Combining all of the studies demonstrated a pooled study population of 1230 patients with the incidence of bacterial infection of 41%. Children with bacterial pneumonia were significantly more likely to have serum CRP concentrations exceeding 35-60 mg/L than children with nonbacterial infections (odds ratio = 2.58, 95% confidence interval = 1.20-5.55). Sensitivity analysis demonstrated that this difference was robust. There was significant heterogeneity among the 8 studies (Q = 37.7, P<0.001, I2 = 81.4) that remained throughout the sensitivity analysis. CONCLUSIONS: In children with pneumonia, serum CRP concentrations exceeding 40-60 mg/L weakly predict a bacterial etiology.   The utility of serum C-reactive protein in differentiating bacterial from nonbacterial pneumonia in children: a meta-analysis of 1230 children.  Pediatr Infect Dis J. 2008;27(2):95

综合了一些研究，Uptodate上儿童肺炎临床特点与诊断的作者最后得出下面的结论，听起来比较中肯：不能单靠CRP来区分肺炎是细菌还是病毒，但可以用来跟踪病程，观察疗效和决定什么时候停药。

Acute phase reactants should not be used as the sole determinant to distinguish between viral and bacterial etiologies of CAP but may be helpful in following the disease course, response to therapy, and in determining when therapy can be discontinued.  Via Uptodate

总之：C反应蛋白正常的话，细菌感染的可能性不大，但增高绝不意味着就一定是细菌感染：病毒感染往往也会高到10~40mg/L，随着CRP进一步升高，细菌感染的可能性加大。医生不能单凭这一项指标就给抗生素，那将造成多少滥用！区分细菌和病毒感染不是件容易事，临床需要结合病史、体检和其他检查综合考虑。