Disease screening tandem mass spectrometry positive

This is just an abnormal reminder at the screening level and is not equivalent to a confirmed diagnosis of illness. Current clinical statistics show that more than 90% of such positive results will eventually be judged as false positives, and less than 10% require subsequent medical intervention.

I have been in the neonatal genetic metabolism clinic for almost 6 years, and the most common scene I encountered was the couple coming in with red eyes, clutching the wrinkled plantar blood screening report, and they were unable to speak clearly, so they asked the doctor, "Does my baby have a rare disease?" Last week, a mother who was born in 1997 handed over a report when she came in. Her hands were shaking. She said that she had searched Baidu all night and had searched for the special milk powder and rehabilitation training her child would need in the future. She was just waiting for me to "sentence death" to her.

In fact, many people don’t know that there are too many factors that interfere with the screening results of tandem mass spectrometry. Take the most commonly used newborn foot blood screening as an example. The blood collection time is usually 3-7 days after birth. If the baby is born prematurely, has experienced asphyxiation at birth, has pathological jaundice, or starts breastfeeding late, or has received high-concentration glucose supplementation due to hypoglycemia before, or even if the blood sample has been left at room temperature for a long time, the metabolic indicators may be abnormal. There was a 34-week-old premature baby who stayed in an incubator for a week after birth. When taking plantar blood, he was still receiving intravenous nutrition. It was found that the level of branched-chain amino acids was three times higher. At that time, the parents were so frightened that they could not even sit properly during the confinement period. As a result, they were rechecked after the corrected gestational age was 40 weeks. All indicators were within the normal range, which was purely a false alarm.

Speaking of this, I have to mention that in recent years, the industry has been noisy about the threshold setting of tandem mass spectrometry screening. One group thinks that the current threshold is too loose and the false positive rate is too high. Many families who are good at first have to worry for a month or two after receiving the report. There are even parents with poor psychological quality who cut off normal breast milk from their children before the reexamination results come out and buy special formula powder indiscriminately. Instead, they feed their children malnourished. There have been extreme cases in other places before. Parents gave up their newborn children immediately after receiving a positive result, causing irreparable consequences. This school's view is to increase the threshold appropriately, suppress the false positive rate, and reduce unnecessary social costs and family anxiety.

The attitude of the other group is also very firm: the benefits of early diagnosis and early treatment of rare diseases are too high and they cannot afford to gamble. Take phenylketonuria, the most common disease, for example. If a child diagnosed at birth continues to drink special milk powder until the age of 6, his intelligence, growth and development will be completely the same as that of ordinary children. If the diagnosis is missed, the brain damage will be irreversible by the time he is found to have slow growth at half a year old, and he will have to be cared for by his family for the rest of his life. No one can afford this price. Therefore, their point of view is that they would rather screen for 100 more false positives than miss one true child. The two groups have been arguing for almost ten years, and there is no unified conclusion yet. They can only fine-tune the thresholds based on their own screening data and try to find a balance between accuracy and coverage.

Don’t be confused if you really get a positive report. First, turn to the page of abnormal items in the report to see if a single indicator is slightly higher or if multiple indicators are doubled and abnormal, and then make a judgment based on your own physical condition (or the condition of the baby). If a single indicator is just a little bit high, and there is nothing uncomfortable about it. The baby is feeding well, gaining weight normally, and does not have strange symptoms such as frequent vomiting, lethargy, or convulsions. Then it is most likely to schedule a reexamination first. For the reexamination, blood can be taken again. If it is still abnormal, a urine gas chromatography-mass spectrometry test will be added. If you are really unsure, do a genetic test. Don't just randomly check and take medicine. I met a 28-year-old girl before. The physical examination at the work unit included a genetic metabolism screening, and it was found that free carnitine was low. She took supplements at home for three months, but the result was still low when she came for a reexamination. When I asked her, I found out that she was a vegetarian all year round and rarely touched red meat and animal offal. She had no discomfort. She was told to eat 2 taels of lean pork every day and took L-carnitine for a month as prescribed by the doctor. After another test, everything was normal. It is not a genetic metabolic disease at all.

Of course, you can’t take it completely seriously. If you have unexplained developmental delays, repeated vomiting, or muscle weakness, or have had relatives who died of unexplained causes in the past, or if there are several indicators in the test report that have increased several times, then you still need to be careful and see a specialist in the Department of Genetics and Metabolism for evaluation as soon as possible. Don’t delay.

After all, tandem mass spectrometry is essentially a screening tool, and it cannot be 100% accurate. When you get a positive result, you should be relieved first, and just follow the process for reexamination. Most of the time, it is a false alarm. Don't scare yourself first. If you stay up all night and cannot sleep, it is not worth it.