ตรวจพบแบคทีเรียในปัสสาวะโดยไม่มีอาการ: ใครบ้างที่จำเป็นต้องใช้ยาปฏิชีวนะ?

อัปเดตล่าสุด: สิงหาคม 25, 2026

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A urine culture comes back positive. The person feels completely well — no burning, no urgency, no pain. Should they take antibiotics? For most people the answer is no, and treating anyway causes more harm than it prevents. This is asymptomatic bacteriuria, and it is one of the commonest reasons antibiotics are prescribed when they should not be.

What the term actually means

Asymptomatic bacteriuria is bacteria growing in the urine of someone with no urinary symptoms at all — no pain on passing urine, no frequency, no urgency, no discomfort above the pubic bone. The bacteria are living in the bladder without causing disease, in much the same way that bacteria live on the skin and in the bowel.

Diagnosis requires a proper urine culture, not a dipstick. It occurs in both sexes and becomes steadily more common with age; in elderly residents of care facilities it is the norm rather than the exception. That last fact is the source of most of the trouble on this subject.

The two situations that genuinely need treatment

1. Pregnancy. Untreated bacteriuria in pregnancy carries a real risk of progressing to kidney infection, which is dangerous for mother and baby. Screening with a urine culture is standard at the first antenatal visit, treatment is given if it is positive, and a repeat culture afterwards confirms it has cleared.
2. Before a urological procedure that will break the lining of the urinary tract — a prostate biopsy, or endoscopic surgery such as prostate resection or stone treatment. Instrumenting an infected urinary tract can push bacteria into the bloodstream. Antibiotics are given shortly beforehand, targeted at what the culture actually grew, and stopped afterwards. It is not a long course, and it does not apply to every urological appointment.

A note on preterm birth

An earlier version of this article stated that asymptomatic bacteriuria significantly increases preterm labour. That claim is stronger than the current evidence supports. The association with kidney infection is well established and is the reason treatment is given; the association with preterm birth comes largely from older studies and looks weaker in modern trials. The recommendation to screen and treat in pregnancy is unchanged — the justification for it has simply been stated more accurately here.

Where the mistake is usually made: the older person with confusion

An older person becomes muddled or unsteady. A urine sample is sent, bacteria grow, and antibiotics are started for a urinary tract infection. This sequence happens constantly, and it is usually wrong.

Because bacteriuria is so common in older people, a positive culture in someone who is confused tells you very little on its own. Confusion in an older adult far more often comes from dehydration, a new medication, pain, constipation, poor sleep, a chest infection or a stroke. Labelling it a urinary infection and treating it means the real cause goes unexamined while the antibiotic does nothing — and antibiotics in older people carry their own price, including Clostridioides difficile diarrhoea and interactions with the other medicines they are taking.

The exception is straightforward: if there is fever, new flank or back pain, rigors, or a clear urinary symptom, that is no longer asymptomatic bacteriuria and it does need treating.

Groups where treatment is specifically NOT recommended

Bacteriuria without symptoms is common in each of the following, and in none of them does treating it improve anything.

• Healthy non-pregnant women of any age.
• Older adults living independently or in care, including those with confusion but no urinary symptoms or fever.
• People with diabetes.
• People with a long-term urinary catheter — the catheter will always grow bacteria, and treating it simply selects for more resistant ones.
• People with spinal cord injury using intermittent catheterisation.
• Before surgery that does not involve the urinary tract.

The follow-up advice that used to appear here, and why it has changed

This article previously advised that people who did not need treatment should have regular urine tests, and that a repeat culture should be sent if inflammatory cells appeared. That advice has been removed, because it undoes the point of the article.

Repeatedly testing the urine of someone with no symptoms produces repeatedly positive results, and each positive result creates fresh pressure to prescribe. Inflammatory cells in the urine — pyuria — are extremely common alongside bacteriuria and are ไม่ in themselves a reason to treat or to re-culture in someone who feels well. The current position is simpler and safer: if there is no reason to treat, there is no reason to test. What matters is knowing which symptoms mean something has changed.

Pyuria without bacterial growth is a different question with its own causes — see sterile pyuria.

อาการที่ต้องไปพบแพทย์ในวันเดียวกัน

Bacteriuria stops being asymptomatic the moment any of these appear. In an emergency in Thailand, call 1669.

• มีไข้หรือหนาวสั่น.
• Pain in the flank or back, particularly with fever — this suggests the kidney is involved.
• Vomiting and inability to keep fluids or medication down.
• Burning, frequency or urgency that has newly appeared.
• Any fever during pregnancy, or any positive urine result in pregnancy that has not been acted on.

Related reading: bacteria in your urine without symptoms, in more detail, why bladder infections keep coming back, and preventing recurrent infections without antibiotics.

คำถามที่พบบ่อย

Q1: ปัสสาวะมีเชื้อแบคทีเรียโดยไม่มีอาการคืออะไร

Bacteria growing on a urine culture in a person with no urinary symptoms — no burning, no frequency, no urgency, no pain above the pubic bone. The bacteria are colonising the bladder rather than causing disease. It becomes more common with age and is very common in people with long-term catheters.

Q2: Does it always need antibiotics?

No. For most people antibiotics provide no benefit and carry real costs — side effects, disruption of normal bowel bacteria, and the selection of resistant organisms that make a future genuine infection harder to treat. Treatment is recommended in two situations only: pregnancy, and before a urological procedure that breaks the lining of the urinary tract.

Q3: My elderly relative is confused and their urine test was positive. Is that a urinary infection?

Usually not. Bacteria in the urine are so common in older people that a positive culture does not explain confusion by itself. Unless there is fever, flank pain, rigors or a definite urinary symptom, the confusion should be investigated properly — dehydration, a new medicine, pain, constipation, a chest infection and stroke are all more likely explanations, and treating the urine means the real cause is missed.

Q4: How is it diagnosed?

By urine culture showing significant bacterial growth in someone with no symptoms. A dipstick is not sufficient. The more important point is that in most people there is no reason to send the test at all — screening someone with no symptoms is what starts the cycle of unnecessary treatment.

Q5: Are inflammatory cells in the urine a reason to treat?

No. Pyuria commonly accompanies bacteriuria and does not by itself indicate an infection requiring antibiotics in someone who feels well. An earlier version of this article suggested repeating the culture when pyuria appeared; that advice has been withdrawn.

Q6: What happens if it is left untreated in a healthy non-pregnant woman?

In most cases nothing. It does not progress reliably to symptomatic infection and does not damage the kidneys, and it often clears on its own. What matters is recognising the symptoms that mean the situation has changed, rather than monitoring the urine of someone who feels well.

การนัดหมายเพื่อปรึกษา

If you have been told you have bacteria in your urine and are unsure whether treatment is needed — particularly if you are pregnant or have a procedure coming up — Dr. Soarawee Weerasopone sees patients at โรงพยาบาลกรุงเทพ สำนักงานใหญ่ และที่โรงพยาบาล สมิติเวช ศรีราชา ในจังหวัดชลบุรี เมื่อวันที่ 088-022-1445. Bring the culture result itself, and any antibiotics already taken.

โรงพยาบาลกรุงเทพฯ มีบริการแพทย์ทางไกลสำหรับผู้ป่วยที่ไม่สามารถมาพบแพทย์ด้วยตนเอง รวมถึงผู้ป่วยต่างชาติ กรุณาแจ้งล่วงหน้าทางอีเมลไปยังแผนกศัลยกรรมทางเดินปัสสาวะที่ bhquro@bdms.co.th. Samitivej Sriracha ให้บริการเฉพาะการพบแพทย์ด้วยตนเองเท่านั้น สอบถามเรื่องค่าใช้จ่ายได้ที่โรงพยาบาลโดยตรง ไม่ใช่ผ่านทางเว็บไซต์นี้.

ข้อจำกัดความรับผิดชอบ เนื้อหานี้ถูกเขียนและตรวจสอบโดย นพ. สรวีร์ วีระโสภณ ซึ่งเป็นแพทย์ผู้เชี่ยวชาญที่ได้รับการรับรองจากคณะกรรมการที่ โรงพยาบาลกรุงเทพ สำนักงานใหญ่ และมีวัตถุประสงค์เพื่อการศึกษาเท่านั้น เนื้อหานี้ไม่ใช่คำแนะนำทางการแพทย์ การวินิจฉัย หรือใบสั่งยาสำหรับบุคคลใดทั้งสิ้น และไม่มีการให้คำแนะนำ การวินิจฉัย หรือใบสั่งยาผ่านช่องทางส่งข้อความส่วนตัวหรือสื่อสังคมออนไลน์ นพ. สรวีร์ ไม่มีบัญชีสื่อสังคมออนไลน์สาธารณะใดทั้งสิ้น; บัญชีใดที่เสนอการปรึกษาส่วนตัวในชื่อของเขาเป็นการหลอกลวง ในกรณีฉุกเฉินในประเทศไทย ให้โทร 1669.