WBC, CRP, and PCT test indicators for judging infection, and they can be elevated to varying degrees when infection occurs, but they are often inconsistent in clinical work, so how should we analyse these inconsistent results?
1. Blood routine WBC and neutrophil ratio can be used to distinguish bacterial infections from non-bacterial infections, but it should be noted that the sensitivity and specificity are poor, and the results are affected by a variety of factors.
For example:
When severe infection is present, a decrease in the total number of WBCs may occur;
At the same time, non-infectious diseases can cause elevated cytokines and granulocyte colony-stimulating factors, both of which can cause an increase in WBC, so their accuracy is low.
2. CRP is a non-specific acute phase protein produced by the liver, which begins to increase when bacterial infection begins to increase at 6-12 hours and reaches its peak at 24-48 hours, and its sensitivity is better than that of WBC.
However, CRP is not highly specific for diagnosing bacterial infections, and it can also be significantly elevated in some viral infections such as infectious mononucleosis, postoperative surgery, autoimmune diseases (such as rheumatic fever, systemic lupus erythematosus, etc.), cardiovascular system diseases, malignant tumours, etc., so it is easy to cause misdiagnosis.
3. PCT is the precursor of calcitonin, which is produced and secreted by thyroid C cells under normal physiological conditions, but is not released into the blood, so the level is very low in healthy people, generally less than 0.1ng/ml.
After being stimulated by inflammation, it is mainly secreted by liver macrophages, monocytes, lymphocytes in lung and intestinal tissues, and neuroendocrine cells, selectively responds to systemic bacterial infection, fungal infection and parasitic infection, which can be detected 4 hours after bacterial infection, rises sharply within 6 hours, and maintains this level within 6-24 hours, and the level is positively correlated with the severity of infection.
The clinical value and test of PCT is mainly as follows:
1. It can be used to guide the differential diagnosis of bacterial infection.
Procalcitonin is generally considered to be higher in patients with bacterial infections than in fungal infections, viral infections, and atypical pathogens.
The plasma PCT concentration is higher than 0.05 ng/ml and can reach up to 0.1 ng/ml, but generally does not exceed 0.3 ng/ml.
The cut-off value for the diagnosis of PCT in patients with sepsis is more than 0.5 ng/ml, and the mass concentration of PCT in patients with severe sepsis and septic shock fluctuates between 5~500 ng/ml.
Very few patients with severe infection have plasma PCT levels above 1000 ng/ml.
2. PCT can also be used to guide anti-infective therapy.
Compared with traditional anti-infective therapy, dynamic monitoring of PCT to guide anti-infective therapy can reduce the time of antimicrobial use.
When the PCT < 0.1 ng/ml, it indicates that there is no bacterial infection, and antimicrobial drugs should be avoided at this time;
When the PCT level is between 0.1~0.25 ng/ml, it means that there is probably no bacterial infection, and it is not recommended to use antimicrobial drugs at this time, and it should be comprehensively judged according to the clinical situation;
When the PCT ≥ 0.25 ng/ml, there is a high probability of bacterial infection, and antimicrobial drugs are recommended;
When the PCT ≥ 0.5 ng/ml, it indicates that there is definitely a bacterial infection and antimicrobial drugs are strongly recommended.
The use of PCT to guide anti-infective therapy has been reported to be associated with a significant reduction in antimicrobial dosage, with an estimated 47% reduction in antimicrobial cost per patient.
In summary, the rapid diagnostic test of WBC, CRP and PCT will increase after bacterial infection, but the inconsistent results of WBC, CRP and PCT may occur in clinical practice, and the combined application of WBC, CRP and PCT can improve the sensitivity, specificity and accuracy of early diagnosis of bacterial infection, so as to guide clinical treatment more reasonably and effectively, shorten the application time of antimicrobial drugs, and reduce medical costs.
