A GP has been ordered to pay £3,000 compensation for not referring a patient, who turned out to have cancer, to a specialist sooner.
Public Services Ombudsman for Wales Peter Tyndall ruled Dr Ramesh Bohra, of Swansea, should have referred the woman within two weeks of reporting blood in her urine in 2007.
The 55-year-old - referred to as Mrs K - died in hospital in September 2009.
Dr Bohra apologised for not following clinical guidelines.
Her son complained to the ombudsman saying that a timely referral may have prevented her death.
His complaint was upheld and the ombudsman ruled Dr Bohra had made a "significant error" and should apologise and pay £3,000 compensation.
Instructions issued by the National Institute for Clinical Excellence (NICE) state that any patient who finds blood in their urine should be seen by a relevant specialist within two weeks.
Mr Tyndall said: "We will never know how an earlier diagnosis of cancer may have affected the outcome for Mrs K.
"I consider that this will be a source of distress for Mr K for the rest of his life. He has my sincere sympathy.
"I also acknowledge the apologies and condolences offered to Mr K by the GP."
Mr Tyndall consulted a doctor to advise him on the medical side of his investigation.
"Despite the uncertainty, my adviser has said that an earlier referral would have given Mrs K a better chance of recovery as evidenced by the five year survival rate data compiled by Cancer Research UK."
Mrs K first visited Dr Bohra at the Clase Surgery in Clase, Swansea, in 2006 and saw him several times complaining of stomach pains and nausea before she was eventually diagnosed in September 2007 after a scan at a hospital.
The GP initially treated her for what he thought was nausea, then a urine infection, and later gall stones.
The investigation found the surgery's only record of Mrs K reporting blood in her urine was on 20 March 2007 and that should have been enough to prompt the referral.
Instead, an ultrasound was ordered but the letter requesting it went astray for six weeks.
She eventually had a scan on 28 August 2007 and was diagnosed with Stage 4 kidney cancer (the most advanced) days later.
The hospital reported Mrs K had a history of blood in her urine for six to seven months.
A summary of the ombudsman's report said: "Clinical guidelines indicate that blood in the urine should lead to such a referral under what is known as 'the two week rule'... By not doing so in this case, the GP made a significant error."
Dr Bohra told the ombudsman the surgery had investigated the failed attempt to arrange the scan and put measures in place to ensure it did not happen again.
He admitted he was unaware of the two-week rule when it came to referrals.
He said: "I would like to apologise for not having acted in accordance with accepted guidance."