The patient, a 17-year-old female, was admitted to the hospital with fever of unknown origin and was later diagnosed with infective endocarditis and given cefmetazole sodium (2 g, tid) and amikacin (0.4 g, qd) intravenously. After 7 days of treatment, the body temperature was normal and all other tests were normal, but the routine blood test showed leukocytes of 2.5×109/L. Why did this patient have low leukocytes despite a period of antimicrobial therapy? Shouldn’t a patient with a normal infection have elevated white blood cells? After reading this article, maybe you will find the answer. Routine blood tests, the first of the three routine tests, are one of the common tests used by doctors to diagnose medical conditions. The most commonly used items on a routine blood test include hemoglobin measurement, red blood cell count, white blood cell count and white blood cell sorting count. White blood cell count White blood cell count (WBC) is normally 4.0-10.0 x 109/L in adults, 15.0-20.0 x 109/L in newborns, and 5.0-12.0 x 109/L in infants 6 months-2 years old. 1. Leukocytosis The first thing that comes to mind with leukocytosis is the presence of infection, but you may not know that chronic leukemia, malignancy, uremia, diabetic ketoacidosis, and chemical poisoning are the most common causes of leukocytosis. The first thing you may not know is that chronic leukemia, malignancy, uremia, diabetic ketoacidosis and acute poisoning by chemical drugs can also cause leukocytosis. Leukocytosis needs to be taken seriously because it can be a symptom of chronic leukemia, which, if left untreated, can lead to accelerated or acute lesions of slow-growing leukemia. In addition to these pathological causes, there are also physiological causes such as leukocytosis around the time of menstruation, pregnancy, women during childbirth, strenuous exercise, excitement, and alcohol consumption. Therefore, when you see elevated leukocytes, do not jump to a diagnosis, it may be caused by physiological reasons. 2, leukopenia Leukopenia, as a doctor, perhaps your first thought is still pathological disease, but also be careful not to ignore the physiological and drug causes. Influenza, measles, granulocyte deficiency, cataracts and leukemia can all cause leukopenia. Of course, there are also some “false positives” that are easily overlooked. When a patient is taking sulfonamides, antipyretics, some antibiotics (such as cephalosporins), antithyroid or antitumor drugs, it can cause leukopenia, which can be recovered by discontinuing them. And for chemotherapy patients due to the adverse effects of chemotherapy drugs, there will also be a decrease in white blood cells, you can take some white-raising drugs. 3.$ Leukocyte classification count Leukocytes are a “big family”, divided into neutrophils, eosinophils, basophils, monocytes and lymphocytes. The normal values of neutrophils are 50% to 70%, eosinophils are 0.5% to 5%, basophils are 0 to 1.0%, lymphocytes are 20% to 40%, and monocytes are 3% to 8%. (1) Increased Neutrophilia is the most common, and because it is often caused by acute, septic infections, it can be an indicator of infection along with leukocytes. In contrast, normal leukocytes and high neutrophils are not necessarily an infection, as neutrophils fluctuate physiologically. Of particular concern is the finding that patients with neutrophilia have a higher incidence of coronary heart disease, which is often severe, and a higher mortality rate in patients with cancer. In addition to the pathological diseases that increase eosinophilia, there is also an increase when drugs such as midazapril, cefradine and cefuroxime sodium are applied. (2) Decrease When patients have diseases such as typhoid fever and paratyphoid fever, it may cause a decrease in each cell of the leukocyte classification. And neutropenia is caused when patients take antineoplastic drugs, benzodiazepine sedatives, and antiepileptic drugs. And eosinophilic or basophilic granulocytopenia can occur with long-term application of drugs such as adrenocorticosteroids or candesartan. Erythrocyte count Erythrocytes are an important “player” in the blood, with a normal value of (4.09~5.74)×1012/L for men and (3.68~5.74)×1012/L for women. 1. Erythrocytosis In addition to the unexplained chronic myelodysplasia that causes true erythrocytosis, erythrocytes can reach a maximum of (7~12)×1012/L. There are also some physiological There are also physiological causes of erythropoiesis, such as an increased rate of erythrocyte release from the bone marrow during hypoxia and plateau life. There is also a relative increase in red blood cells, when a large amount of water loss such as vomiting, diarrhea, sweating, shock, etc., the amount of plasma decreases, the blood is concentrated, then the concentration of each component in the blood increases accordingly. However, it is only a temporary phenomenon, and the red blood cells tend to normalize after the symptoms are relieved. Which can be measured by the red blood cell pressure product to understand the degree of blood concentration, as a clinical basis for the amount of rehydration. 2.Red blood cell reduction Different causes of anemia such as aplastic anemia, blood loss anemia, etc. can cause a decrease in red blood cell count. Hemoglobin Hemoglobin (Hb) – the main component of red blood cells, its increase or decrease has the same clinical significance as that of red blood cell increase or decrease, and can better reflect the degree of anemia. Normal values are 131~172 g/L for men and 113~151 g/L for women. 1. Increased hemoglobin Chronic pulmonary heart disease, true erythrocytosis, plateau disease and other pathological causes can cause increased hemoglobin. In cases of massive water loss and severe burns, hemoglobin increase can also be caused by blood concentration, but this condition requires special attention and may mask the symptoms of anemia. There are other conditions that are often overlooked, such as when the patient is taking drugs like sodium para-aminosalicylate, primaquine, vitamin K, nitroglycerin, etc., which can also increase Hb, so the effect of taking these drugs should be excluded when diagnosing the disease. 2. Hemoglobin reduction (1) The degree of hemoglobin reduction = the degree of red blood cell reduction, mostly seen when bleeding. And because hemoglobin can interact with certain substances to form a variety of hemoglobin derivatives, it can also be used to diagnose certain blood system diseases. (2) The degree of hemoglobin reduction > the degree of erythrocyte reduction, which is mostly seen in iron deficiency anemia. (3) Hemoglobin reduction < erythrocytopenia, most often seen in megaloblastic anemia. Hemoglobin measurement can also provide a basis for determining the severity of anemia, with >90 g/L being mild, 60-90 g/L moderate, 30-59 g/L severe, and <30 g/L very severe anemia. Platelet count Platelets can produce a variety of platelet factors, which are involved in blood coagulation. Normal values are (100~300)×109/L for men and (101~320)×109/L for women. 1. Pathological causes A variety of conditions can cause platelet reduction, such as bone marrow hematopoietic dysfunction, aplastic anemia, etc. can reduce platelet production. Cirrhosis and hypersplenism can cause excessive platelet destruction; splenomegaly and various causes of hemodilution can cause abnormal platelet distribution. In addition to pathological diseases that cause thrombocytopenia, there is also transient thrombocytosis seen in acute hemorrhagic anemia, post-spleen removal, fracture, post-hemorrhage and other traumas. 2, drug-induced thrombocytopenia There are also drugs that cause poisoning or allergies when taking some drugs can also cause thrombocytopenia. For example, when taking chloramphenicol has a myelosuppressive effect, can cause thrombocytopenia; anti-platelet drugs such as aspirin can also cause thrombocytopenia; there are some anti-tumor drugs, antibiotics, sulfonamides can also cause thrombocytopenia. So let's go back to the case at the beginning of the article, it will be found that the patient's leukopenia is more likely to be affected by cefmetazole drugs. Of course in routine blood tests, it is not the abnormality of one indicator that confirms the diagnosis of having a certain disease, but the combination of several tests is needed to support the evidence of a certain disease.