Why do I always have to draw blood when I go to the hospital? What diseases can a blood test detect? One answer
Do you believe in the thing that "one drop of blood can detect cancer"?
The person who created the concept of "blood test for cancer" is a 19-year-old American girl named Elizabeth Holmes. In 2003, she dropped out of Stanford University and founded a blood testing company, Theranos, which claims to be able to detect whether a person has cancer by collecting blood from a fingertip .
This subversive point of view has attracted intense attention. The valuation of Theranos has continued to rise, soaring to $9 billion, and Elizabeth Holmes has even been hailed as "the next Jobs."
However, the false will never become true. A questioning article in the "Wall Street Journal" in 2015 pointed out that most of Theranos's blood tests were carried out through traditional inspection methods , and the results could not guarantee accuracy. Since then, the "myth" created by Elizabeth has gradually collapsed.
In September 2018, Theranos was dissolved. In August 2020, Elizabeth went to trial and was convicted on January 3 this year.
Although Elizabeth's lies have been exposed, the concept of "one drop of blood for cancer detection" is still prevalent in China. Many testing institutions claim that one drop of blood can detect dozens of cancers and package it as an advanced detection technology. Can the "blood test for cancer" be realized?
1. Is the "blood test for cancer" reliable?
After Elizabeth Holmes, another company issued a statement saying that it has developed a blood test cancer product Galleri, which can detect many cancers that cannot be detected by conventional screening.
The company let 6,621 participants over the age of 50 use the Galleri kit, and the test results showed that 92 of them might have cancer, and 35 of them were confirmed to have cancer, and the other 57 were false positives .
One of the 35 cancer patients had breast cancer and endometrial tumors at the same time, so a total of 36 cancers were detected by the Galleri kit. Unexpectedly, 14 of these cancers were too early to be detected by conventional screening , and 26 were not included in general cancer screening programs.
Although Galleri's experimental results are encouraging, this technology still has false positives and many details. It is not currently on the market, nor can it replace routine cancer screening.
In fact, the principle of blood test for cancer is reliable. When cancer cells die and disintegrate, oncogenes spread into the blood. If we can detect these oncogenes, we can find traces of cancer cells .
However, the "blood test for cancer" has exaggerated the role of blood tumor markers. At present, there is no blood marker in the world that can diagnose tumors 100%.
Tumor markers, including serum carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), etc. By checking their levels in the blood, we can find out whether there is any abnormality in the blood, and infer whether the body has a tumor risk, but the real diagnosis still needs to go through a lot of inspections.
All in all, cancer is very complicated, and blood tests alone are not rigorous, and imaging and pathological examinations are needed to draw a conclusion .
2. What diseases can be detected by blood drawing in the hospital?
When many people go to the hospital for physical examination, it is necessary to draw blood for examination, and often there are several tubes in one draw. Why do blood tests require so much blood?
The liquid component of blood is plasma, in which blood cells are suspended, so plasma and blood cells are the components of blood. In addition to containing a large amount of water, plasma also includes chemical components such as albumin, globulin, inorganic salts, amino acids, etc., transports lipids and nutrients, and participates in immunity, blood coagulation and anticoagulation functions.
The main components of blood cells are red blood cells, white blood cells, and platelets, each of which performs its own duties and flows to the whole body with the blood.
Changes in blood components are often affected by physiological and pathological changes in the body , so it is very important to detect blood components clinically.
Then why do you have to draw several tubes every time you draw blood?
This is related to the physical examination items. Different indicators such as blood routine, blood sugar, and immunity have different detection methods. If there are more blood test methods involved, the more blood is needed . And sometimes the detection will not be successful the first time, which should also be taken into account.
As for the remaining blood after the test, it is usually stored for about a week, because if there is any objection to the test result, the sample can be taken out for another test. If there is no problem, the excess blood belongs to medical waste , and after recording, it will be sterilized at high temperature before being discarded.
So what diseases can be detected by blood tests?
Dai Dai, deputy chief physician of the Department of Orthopedics at the Affiliated Hospital of Yangzhou University, said that blood tests can be subdivided into routine blood tests, organ function tests, hormone blood tests, etc., so there are still many diseases that can be detected.
1. Blood routine examination
It mainly checks basic indicators such as blood lipids, blood pressure, and blood sugar. By comparing them with reference values, it can be inferred whether the patient meets the symptoms of metabolic diseases such as hypertension, hyperlipidemia, and hyperglycemia, so as to conduct further inspections.
2. Organ function check
Check whether the internal organs are abnormal, such as the content of transaminase and bilirubin in the blood, which can diagnose whether the liver is healthy, and the heart health can also be judged by the enzyme content.
3. Hormone blood test
Check the hormone content in the blood to judge the hidden dangers of the disease. For example, if the content of thyroid hormone and adrenal hormone is abnormal, you may suffer from endocrine diseases such as hyperthyroidism and hypothyroidism.
3. How long does it take to draw blood on an empty stomach?
Before the blood draw, the doctor will usually tell you not to eat, and the blood draw must be on an empty stomach, so how long does the fasting take? Can't even drink a sip of water?
In fact, the fasting test is artificially stipulated, and there are two main purposes for this. On the one hand, the value of some inspection items will change to varying degrees after eating . In order to make the results comparable, fasting needs to be used as a reference standard, so that by comparing the inspection value with the reference value, it is possible to intuitively judge whether there is an abnormality.
On the other hand, after eating, the blood lipid content will inevitably change. Especially within two hours after a high-fat diet, blood lipid levels rise sharply . At this time, blood tests may interfere with the results and increase errors.
Therefore, in order to obtain a more accurate diagnosis, it is necessary to keep an empty stomach when performing at least five testing items, including blood lipids, fasting blood glucose and other glucose metabolism items, blood rheology examination, platelet aggregation rate, and bone metabolism markers such as osteocalcin .
How long do you have an empty stomach?
The "Guidelines for the Collection of Venous Blood Specimens" pointed out that the inspection that requires fasting blood collection is best arranged between 7:00 am and 9:00 am. It is required that you should not eat for at least 8 hours before the collection . Generally, it is best to fast for 12-14 hours, but you cannot more than 16 hours.
Although you can't eat, you can still drink a small amount of water, and you can only drink plain water, and you can't drink beverages, tea, wine, etc.
Especially patients with chronic diseases who need to take medicine on time should also take medicine with a small amount of plain water, and do not stop taking medicine because of blood draw.
Xiao Jiu reminded that after the blood is drawn, you should pay attention to rest and maintain adequate sleep. The blood of the human body can be regenerated, so there is no need to worry about the impact of blood pumping on the body, and there is no need to supplement with big fish and meat, just the right amount of nutrition is enough.
references:
[1] Is the "blood test for cancer" reliable again? Sanlian Life Weekly. 2022-09-29
[2] Why do you draw blood as soon as you arrive at the hospital? What diseases can a blood test detect? Answers from Doctors. Endocrinology Channel in the Medical World. 2022-08-06
[3] How long does it take to draw blood on an empty stomach? The National Health and Medical Commission gives a set of standard answers. Life Times. 2020-11-05
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