Restharn: Warum wir messen müssen ?

Zuletzt aktualisiert: 18. Mai 2026

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Patients at my urology office frequently ask: “Why does the doctor need us to do a residual urine (RU) measurement?” Abnormal urination can arise from many causes, and one important factor is the inability of the urinary bladder to completely empty after voiding — leading to urine stasis inside the bladder.

• Urologiezentrum Bangkok Krankenhaus Thailand Online buchen 02-310-3009 bhquro@bdms.co.th
• Krankenhaus Samitivej Sriracha Chonburi 088-022-1445

Previously, RU measurement required inserting a urethral catheter after the patient finished voiding to measure the remaining volume in milliliters. Today, ultrasound has replaced this invasive method. The patient undergoes an initial ultrasound scan, then voids in the restroom, then has a repeat ultrasound to measure the remaining bladder volume. The radiologist reports RU in milliliters — the same unit as the old catheter method, but completely non-invasively.

The limitations of ultrasound-based RU measurement include: (1) Overestimation if not measured within 10 minutes of voiding, as the kidneys continuously produce urine; and (2) Operator dependency, as the radiologist must manually measure bladder dimensions to calculate volume.

Restharn normal values by age group

• Adults: RU < 50 mL = adequate emptying; RU > 200 mL = inadequate emptying
• Children: RU > 20 mL = inadequate emptying
• Elderly: RU 50–100 mL = normal emptying (age-related bladder changes allow higher thresholds)

When elevated RU is found, the causes must be thoroughly assessed — including neurogenic, mechanical (obstruction), medication-related, infectious, or inflammatory etiologies. Treatment is then individualized to each patient. RU > 100 mL has been associated with an increased risk of urinary tract infection.

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Frequently Asked Questions About Residual Urine Measurement

What is residual urine and why does the doctor measure it?

Residual urine (RU) is the volume of urine remaining in the bladder after voluntary voiding is complete. It is measured to assess bladder emptying efficiency. An elevated RU indicates that the bladder is failing to empty adequately, which can result from bladder outlet obstruction (e.g., BPH in men), neurogenic bladder dysfunction, detrusor underactivity, or medication side effects. RU measurement is a key diagnostic tool in the evaluation of lower urinary tract symptoms.

What is the normal residual urine volume?

Normal values differ by age group: in adults, RU under 50 mL is considered adequate emptying, while over 200 mL indicates inadequate emptying. In children, RU should be under 20 mL. In the elderly, RU of 50–100 mL is considered acceptable due to age-related changes in bladder contractility. RU above 100 mL in adults is associated with an elevated risk of urinary tract infection.

How is residual urine measured today?

Residual urine is now measured non-invasively by bladder ultrasound. The patient undergoes an initial ultrasound scan, then voids in the restroom, and immediately has a repeat ultrasound to measure the remaining volume. This should ideally be done within 10 minutes of voiding to avoid overestimation from ongoing urine production. Bladder ultrasound has replaced the older method of urethral catheterization, which was invasive and uncomfortable.

If you have concerns about incomplete bladder emptying, frequent urination, or urinary tract symptoms, Dr. Soarawee Weerasopone offers specialist consultations at Bangkok Hospital Headquarters. Beratungstermin buchen.

**Haftungsausschluss:** Dieser Inhalt wurde von Dr. Soarawee Weerasopone, einem Facharzt für Urologie am Bangkok Hospital Headquarters, verfasst und überprüft. Er dient ausschließlich Bildungszwecken und stellt keine medizinische Beratung dar. Konsultieren Sie immer einen qualifizierten Mediziner, bevor Sie eine medizinische Behandlung beginnen.