보이지 않는 혈액이 소변에 함유되어 있는 이유: 미세혈뇨의 의미

최종 업데이트: 2026년 8월 27일

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A urine test is part of almost every health-check package, which means a great many people are told they have red blood cells in their urine having had no symptoms and no reason to think anything was wrong. Most of the time the explanation is harmless. The purpose of the assessment is to be sure of that rather than to assume it.

A correction to the reassurance this page used to give

The earlier version of this article said, in effect, don’t worry — if it were a real problem you would see the blood with your own eyes. That is not true, and it has been removed.

Bladder cancer frequently produces bleeding that is only ever detectable under a microscope, particularly in its early stages. The reassurance was well meant and it is exactly the sentence that persuades someone to skip the follow-up appointment. The accurate version: most causes are benign, a minority are not, and which is which cannot be judged from how the urine looks.

What counts as microscopic haematuria

Three or more red blood cells per high-power field on a properly collected specimen examined under the microscope. Two points about that definition matter and were stated differently in the earlier version.

• A dipstick result is not enough. A stick that reads positive for blood must be confirmed by looking down a microscope, because several things turn a dipstick positive without any red cells being present.
• Repeat testing is not required to make the diagnosis. The earlier version described needing two consecutive tests over at least seven days; current guidance defines it on a single adequate specimen. A repeat is useful for a different purpose — excluding contamination.

Where the blood comes from

1. Contamination during collection — the commonest explanation of all, including menstruation and a poorly taken sample.
2. Kidney — stones, a mass, infection, and kidney diseases that are treated by physicians rather than surgeons.
3. Ureter — stones, or a tumour of the lining.
4. Bladder — stones, tumour, 전염병.
5. Prostate — benign enlargement, 전염병, cancer.
6. Urethra — stones, infection, or narrowing.
7. Vigorous exercise, which can cause transient haematuria that settles on repeat testing.

One misconception worth naming: taking a blood thinner does not explain blood in the urine. Anticoagulation may make an existing source bleed more visibly, but it does not create one, and a man on warfarin or a newer anticoagulant with haematuria needs the same assessment as anyone else. Attributing it to the tablets is a recognised route to a delayed diagnosis.

How far the investigation goes depends on your risk

The earlier version said CT with contrast is the definitive test and is what answers the question. That inverts the guideline it cited, and it has been corrected.

The central change in the 2020 American Urological Association guidance was precisely to stop sending everyone for CT. Instead, patients are placed in a low, intermediate or high risk group, and the investigation is matched to it — because CT carries a substantial radiation dose and a contrast load, and most people with a few red cells in the urine do not need one.

What determines the group:

• 나이, 그리고 being male.
• Smoking history — the single strongest modifiable risk factor for urothelial cancer, and the one most often not asked about.
• How many red cells, and whether it has been found repeatedly.
• Any previous episode of visible blood in the urine.
• 직업적 노출 to dyes, rubber, leather or industrial chemicals, sometimes decades earlier.
• Previous pelvic radiotherapy, chemotherapy with cyclophosphamide, a long-term catheter, or chronic irritative urinary symptoms.

Lower risk may reasonably mean a repeat urine test, or an ultrasound, rather than a CT and a telescope. Higher risk means the full assessment — imaging of the kidneys and ureters, and inspection of the bladder.

The part that was missing entirely: looking in the bladder

Cystoscopy did not appear anywhere in the earlier version, and no scan replaces it.

CT does not reliably show a flat tumour on the bladder lining. Carcinoma in situ can be invisible on imaging and obvious through a telescope, so for anyone in the intermediate or high risk group the assessment is imaging 및 a flexible cystoscopy — a few minutes, awake, in a clinic room. A normal CT is not, by itself, an all-clear.

When it is the kidney rather than the plumbing

Some blood in the urine comes from the filtering tissue of the kidney rather than from anywhere a urologist can see. The clues are protein in the urine, abnormal-looking red cells or casts, a raised creatinine, or high blood pressure — and that combination belongs with a kidney physician, in parallel with the urological assessment rather than after it.

If everything is normal

Most assessments find nothing, and that is a genuine result rather than a failure to look hard enough. The urine is then rechecked, and follow-up can be stopped once repeat testing has come back clear.

What matters afterwards: if visible blood ever appears, that is a new event and needs assessing again regardless of how reassuring the previous work-up was.

정기 진료가 아니라 바로 주의가 필요한 증상

태국에서 응급 상황이 발생하면 다음 번호로 전화하십시오: 1669.

• Blood you can see, with or without clots — this is a different and more urgent problem than microscopic haematuria, and painless visible bleeding is more concerning rather than less.
• Clots blocking the flow, or inability to pass urine.
• Fever with flank pain.
• Unexplained weight loss, or new bone pain, alongside blood in the urine.
• Severe flank pain with vomiting, which suggests a stone.

Frequently Asked Questions About Microscopic Haematuria

Is it dangerous?

Usually not — contamination and benign causes account for most of it. But it cannot be dismissed on appearance, because early bladder cancer often bleeds only microscopically. An earlier version of this article suggested a real problem would be visible to the naked eye; that was wrong and has been removed.

Do I need a CT scan?

Not necessarily. Current guidance stratifies patients into low, intermediate and high risk and matches the investigation to the group — a repeat urine test or an ultrasound may be appropriate at lower risk, reserving CT for those who need it, since it carries a significant radiation and contrast load. Age, sex, smoking history, the amount of blood, any previous visible bleeding and certain exposures determine the group.

My CT was normal. Is that the all-clear?

Not on its own for anyone at intermediate or high risk. CT does not reliably show a flat tumour on the bladder lining, so the assessment includes looking inside the bladder with a flexible telescope — a few minutes, awake, in a clinic room.

I take a blood thinner. Doesn’t that explain it?

No. Anticoagulation can make an existing source bleed more, but it does not create one, and haematuria in someone taking a blood thinner is assessed exactly as it would be otherwise. Assuming the tablets are responsible is a recognised route to a delayed diagnosis.

When can follow-up stop?

Once the assessment has found no cause and repeat urine testing has come back clear. If visible blood ever appears afterwards, that is a new event needing assessment regardless of the earlier result.

진료 상담 예약 안내

Dr. Soarawee Weerasopone은 다음 장소에서 환자를 진료합니다: Bangkok Hospital Headquarters 그리고 촌부리의 Samitivej Sriracha Hospital에서 진료하는 요일: 088-022-1445. Bring the actual urinalysis report rather than a summary, and be ready to say whether you have ever smoked and for how long — that question changes how far the assessment goes.

직접 내원하기 어려운 해외 환자분들을 포함한 환자분들을 위해 Bangkok Hospital 원격진료를 이용하실 수 있습니다. 비뇨기과 이메일로 미리 예약해 주세요: bhquro@bdms.co.th. Samitivej Sriracha는 대면 진료만 가능합니다. 비용에 관한 문의는 이 웹사이트가 아닌 병원에서 답변해 드립니다.

면책 조항: 이 콘텐츠는 Bangkok Hospital Headquarters의 비뇨의학과 전문의인 Dr. Soarawee Weerasopone이 작성하고 감수한 것으로, 교육 목적으로만 제공됩니다. 개인에 대한 의학적 조언, 진단 또는 처방이 아니며, 개인 메시지 채널이나 소셜 미디어를 통해서는 어떠한 조언, 진단 또는 처방도 제공되지 않습니다. Dr. Soarawee는 공개 소셜 미디어 계정을 운영하지 않으며, 그의 이름으로 개인 상담을 제안하는 모든 계정은 사기입니다. 태국에서 응급 상황이 발생하면 다음 번호로 전화하십시오: 1669.