Visible blood in urine — even if painless and gone by the next day — still warrants a check-up

A routine urine test costs just a few dozen yuan, while a urinary-system ultrasound runs around 100–200 yuan. If a doctor deems it necessary, a cystoscopy can be added at a cost of roughly 1,000 yuan.

A study was conducted in the UK using electronic medical records from community general practices (primary care), comparing 4,915 cases of bladder cancer to 21,718 controls. Among those with visible gross hematuria, the proportion eventually confirmed to have bladder cancer is as follows: for those aged 60 and above, it is 2.8%, with a 95% confidence interval (CI) of 2.5 to 3.1. For those aged 40 to 59, it is 1.2%, with a 95% CI of 0.6 to 2.3. The technical name for this proportion is the positive predictive value. Microscopic hematuria, which can only be seen under a microscope, also warrants attention. The odds ratio is 20, with a 95% CI of 12 to 33. For those aged 60 and above, this proportion is 1.6%, with a 95% CI of 1.2 to 2.1. The UK National Health Service (NHS) states that blood in the urine may be a sign of cancer and must be investigated. Even if there are no other symptoms, it is the first occurrence, or the amount is very small, you must make a doctor's appointment as soon as possible.

Price SJ, Shephard EA, Stapley SA, Barraclough K, Hamilton WT (2014). Non-visible versus visible haematuria and bladder cancer risk: a study of electronic records in primary care. British Journal of General Practice, 64(626), e584-e589. https://doi.org/10.3399/bjgp14X681409；NHS. Blood in urine：「Blood in your pee must be checked out because it can be a sign of cancer.」「But do not self-diagnose.」「It may not be blood in your pee if: you've recently eaten beetroot … you're taking a new medicine … it's happening during your period」. https://www.nhs.uk/symptoms/blood-in-urine/；NHS. Symptoms of bladder cancer：「You have blood in your pee, even if: you do not have any other symptoms; it's the first time it's happened; there's only a small amount of blood; you're not sure if it's blood」. https://www.nhs.uk/conditions/bladder-cancer/symptoms/

'No pain' is not a reason to let it pass. The UK National Health Service (NHS) specifies that if there is blood in the urine, you must make a doctor's appointment as soon as possible, even if there are no other symptoms, it is the first time, the amount is very small, or you are unsure if it is actually blood. Painful urination, frequent urination, or fever may indicate a urinary tract infection. Intermittent severe pain from the flank to the groin accompanied by restlessness may indicate stones. However, the NHS also advises against self-diagnosing; you should let a doctor examine you. Redness seen during menstruation, having recently eaten beets, or having just started a new medication means red urine is not necessarily blood. For those taking anticoagulants, do not assume it is caused by the medication; this is the author's suggestion, as the above study did not calculate this specific group separately. The benefit is recorded as 'small' because it only includes the detection rate, without the effect size of 'how much early detection can reduce mortality'.