残留尿の理解：膀胱が空にならない理由

最終更新日： 8月 16, 2026

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Have you ever finished urinating, only to feel like your bladder still is not quite empty? Or noticed your urine stream has grown weak, you are heading to the bathroom far more often, or you keep getting urinary infections? These can all be signs of a common and treatable condition: leftover urine in the bladder, known medically as 残尿, またはPVR。わかりやすい言葉で、それが何であるか、なぜそれが重要なのか、そしてそれに対して何ができるのかをご説明します。.

残尿とは何ですか？

排尿後、少量の尿が膀胱に残ることがあります。これは残尿と呼ばれ、略してPVRとも言います。少量が残るのは完全に正常なことですが、 多すぎる 尿が常に残る場合、それは膀胱や泌尿器のトラブルのサインである可能性があり、注意が必要です。.

どのように測定されるのですか？

The good news: measuring residual urine is quick, painless and done right in the office. The most common method is a simple bladder ultrasound scan — a small handheld device is gently placed on your lower abdomen right after you urinate, and it estimates how much urine is left. No needles or catheters are needed for this test.

As a general guide, only a small amount of leftover urine is considered normal. Larger amounts that consistently stay behind suggest the bladder is not emptying well, and a substantial amount left over is classified as urinary retention, which calls for further evaluation.

One caveat about the number itself. A single high reading is not a diagnosis. The result depends on how full the bladder was to begin with, how soon after voiding the scan was done, and whether you were rushed or self-conscious in an unfamiliar bathroom — all of which are enough to distort it. A genuinely raised residual is one that stays raised on repeat measurement, interpreted alongside symptoms rather than on its own. It is worth knowing this before anyone acts on a single number.

残尿はなぜ問題なのですか？

尿が膀胱に長時間または多量にたまると、いくつかの問題を引き起こす可能性があります：

• Urinary tract infections: stagnant urine is a breeding ground for bacteria, leading to frequent or recurring infections — and a raised residual is one of the things worth checking in a man whose urinary infections keep coming back.
• 膀胱の拡張 a bladder that is constantly overfull can gradually stretch and weaken over time, making it even harder to empty — a vicious cycle, and one reason not to wait years before getting it looked at.
• 腎臓の障害： in severe cases urine can back up toward the kidneys, potentially causing kidney damage or infection.
• 排尿症状の悪化： a frequent urge to go, a weak stream, difficulty starting, or the constant feeling that the bladder is never quite empty.

One presentation that catches people out: chronic retention is often painless. Instead of discomfort, it can show up as leaking — small amounts dribbling through the day, or wetting the bed at night in someone who never did before. It is easy to mistake that for an overactive bladder and treat it in exactly the wrong direction, which is the next point.

残尿が多くなる原因は何ですか？

膀胱が完全に空にならない原因には主に2つあります。つまり、パイプの閉塞か、ポンプの弱りと考えてください。.

1. 閉塞（詰まった配管）

In men, the most common cause is an enlarged prostate (benign prostatic hyperplasia, or BPH), which squeezes the urethra and makes it harder for urine to flow out. In women, pelvic organ prolapse — when pelvic organs shift out of position — can press on the urethra. In either sex, scar tissue from prior surgery, injury or infection (a urethral stricture) can also narrow the passage.

2. 膀胱の筋肉の衰え（弱いポンプ）

Conditions such as diabetes, stroke, Parkinson’s disease, multiple sclerosis or spinal cord injury can damage the nerves that control the bladder muscle, leaving it too weak to squeeze urine out effectively. Ageing itself can gradually reduce bladder strength.

3. Medication — the cause people are most surprised by

A number of everyday medicines weaken bladder contraction or tighten the outlet, and in a bladder that was already borderline they can tip it over. The usual suspects are over-the-counter cold and allergy remedies, some antidepressants, some pain medicines, and drugs used for muscle spasm.

The one worth singling out is the group prescribed for bladder symptoms. Anticholinergic medication for an overactive bladder works by calming bladder contraction — which is precisely the wrong thing for a bladder that already cannot empty. That is why the residual is measured before those tablets are started, not after they fail. If your urgency has been treated for months and things are getting worse rather than better, a bladder scan is a reasonable thing to ask for.

None of this is a reason to stop a medicine on your own. Bring the list to the appointment instead. Whether a drug is contributing, and whether it can be changed, is a judgement made with the doctor who prescribed it — stopping an antidepressant or a heart medicine unilaterally causes far more trouble than a raised residual.

警告サイン：医師の診察を受けるべき時期

以下のいずれかの症状が現れた場合は、速やかに医師の診察を受けてください。

• 突発的な完全な排尿不能 — this is a medical emergency called acute urinary retention. Go to the emergency department immediately; it needs a catheter, and waiting risks the bladder and kidneys.
• Fever or chills alongside difficulty passing urine — an infected, obstructed urinary tract can become serious quickly and needs same-day assessment.
• 新しいあるいは悪化する背中の痛みに加え、脚の筋力低下、鼠径部や内股のしびれ、または排泄コントロールの喪失が伴う症状 — these can signal a serious nerve problem at the base of the spine and require immediate attention, not an outpatient appointment.
• Blood in your urine, even once and even painless.
• 頻尿路感染症.
• 排尿後であっても、膀胱が空になっていないという持続的な感覚。.
• Gradually worsening difficulty urinating over weeks or months, or new leaking or bedwetting.

どのように治療されますか？

治療法は原因と重症度によって異なり、多くの効果的な選択肢があります：

• Medication: alpha-blockers relax the muscle around the prostate and bladder neck to improve flow, and other medicines gradually shrink an enlarged prostate over months. Both have trade-offs worth discussing — dizziness on standing and a change in ejaculation with the first group, and a halved PSA reading with the second, which matters for future prostate testing.
• 薬剤確認： adjusting or stopping a contributing medicine, in consultation with whoever prescribed it.
• Intermittent self-catheterisation: if the bladder muscle is too weak to empty on its own, you may be taught to pass a small, thin tube to drain the urine a few times a day. It sounds daunting and most people learn it quickly — there is a step-by-step guide to it here.
• 外科 for blockages that do not respond to medication, a procedure to open the passage may be recommended. Worth knowing beforehand that prostate surgery commonly changes ejaculation, which is not a complication so much as an expected effect.
• Behavioural strategies: timed voiding (urinating on a schedule), double voiding (going, waiting a moment, then trying again), and cutting back on caffeine and alcohol.

One thing that is いいえ treatment: antibiotics for bacteria found in the urine of someone with a raised residual but no symptoms of infection. That situation is common, and treating it repeatedly does harm without benefit — the reasoning is set out in bacteria in your urine without symptoms.

ご来院の際の流れ

Your urologist will ask about your symptoms, medical history and medications, perform a physical examination, and measure your residual urine with a quick bladder scan. They may also order a urine test to check for infection, and depending on the situation, additional tests such as a urine flow study, blood tests to check kidney function, or imaging of the kidneys. Where the picture is unclear — particularly when it is not obvious whether the problem is a blockage or a weak bladder — urodynamic studies can measure both directly, which matters because the two are treated in opposite directions.

重要なポイント

Residual urine is common and treatable. If you are experiencing urinary symptoms, do not ignore them — early evaluation can prevent complications such as infections and kidney damage, and most causes respond well once the right one is identified. A simple, painless bladder scan is often all it takes to start getting answers.

If you would like an assessment, Dr. Soarawee Weerasopone consults at バンコク病院本部 and at Samitivej Sriracha Hospital, Chonburi — 088-022-1445, with the wider range of conditions set out under 泌尿器科.

バンコク病院の遠隔医療は、来院が困難な患者様（海外からの患者様を含みます）を対象にご利用いただけます。泌尿器科宛てに事前にメールでご手配ください。 bhquro@bdms.co.th. It suits reviewing results and planning follow-up; the bladder scan itself requires an in-person visit, and an inability to pass urine needs an emergency department rather than a teleconsultation. Samitivej Sriracha is in-person only.

お客様からよくいただくご質問

排尿後残尿（PVR）とは何ですか？

Postvoid residual urine is the amount left in the bladder right after you urinate. A small amount is completely normal, but when too much consistently remains it can signal that the bladder is not emptying properly — due to either a blockage or a weak bladder muscle. Left unaddressed it can lead to infections, bladder stretching, and in severe cases kidney problems.

How is residual urine measured, and can the result be misleading?

It is measured with a bladder ultrasound scan placed on the lower abdomen just after you urinate — quick, painless, no needles or catheter. A single reading can mislead, though: it depends on how full the bladder was beforehand, how soon after voiding the scan was done, and whether you felt rushed. A genuinely raised residual is one that stays raised on repeat measurement and fits the symptoms.

膀胱が完全に空にならない原因は何ですか？

Two main causes. A blockage prevents urine flowing out — in men most often an enlarged prostate, in women pelvic organ prolapse, and in either sex scar tissue narrowing the urethra. Alternatively a weak bladder muscle fails to squeeze effectively, often from nerve-affecting conditions such as diabetes, stroke, Parkinson’s disease or spinal cord injury, or from ageing. Medication is a third and frequently overlooked contributor.

Can medication for an overactive bladder make this worse?

Yes, and it is the reason residual urine is measured before those tablets are started. Anticholinergic medication for overactive bladder works by calming bladder contraction, which is the opposite of what a bladder that already cannot empty needs. Over-the-counter cold and allergy remedies, some antidepressants and some pain medicines can have a similar effect. Do not stop any prescribed medicine on your own — bring the list to the appointment and decide with the doctor who prescribed it.

残尿が医学的緊急事態となるのはいつですか？

A sudden, complete inability to urinate is a medical emergency called acute urinary retention — go to the emergency department immediately. Fever or chills alongside difficulty passing urine also needs same-day assessment. And new or worsening back pain with leg weakness, numbness around the groin or inner thighs, or loss of bowel control can indicate a serious nerve problem requiring immediate attention. Blood in the urine and frequent infections warrant prompt assessment too.

Can the bladder be full without any pain?

Yes. Chronic retention is often painless, and instead of discomfort it can appear as leaking — dribbling through the day, or bedwetting in someone who never had it before. This is easily mistaken for an overactive bladder and treated in the wrong direction, which is why measuring the residual comes first.

残尿量が多い場合の治療法はどのように行われますか？

Treatment depends on the cause: medication to relax the prostate and bladder neck or to shrink an enlarged prostate, review of contributing medicines, intermittent self-catheterisation for a weak bladder, surgery for a blockage that does not respond to medication, and behavioural strategies such as timed and double voiding. Antibiotics are not treatment for bacteria found without symptoms of infection.

免責事項 This content is written and reviewed by Dr. Soarawee Weerasopone, a board-certified urologist at Bangkok Hospital Headquarters. It is intended for educational purposes only and does not constitute medical advice. No advice, diagnosis or prescription is given through personal messaging channels or social media. Do not stop or change a prescribed medicine on your own. A sudden, complete inability to urinate is a medical emergency — seek immediate hospital care. Always consult a qualified healthcare professional before starting or changing any medical treatment.