More than 400 people in Malaga were wrongly told they may have had colon cancer due to a faulty lab machine, it has emerged.
According to the regional Health Ministry, the issue originated from a cleaning fluid used by the machine responsible for detecting hidden blood in stool samples, a key test used in bowel cancer screening programmes.
Officials said the problem emerged following maintenance work on the analyser.
As a result, some samples recorded artificially elevated readings, causing the equipment to incorrectly classify them as positive for traces of blood.
The Junta de Andalucia stressed that the incident did not generate any false negative results, meaning potential cancer cases were not missed.
Instead, the malfunction increased the number of positive results by mistake, leading some patients to believe further investigation was needed when their tests should have been negative.
Once the cause was identified, technicians corrected the fault, strengthened quality control procedures and ordered all tests carried out during the affected period to be repeated.
The issue first came to light after the Servicio Andaluz de Salud noticed a higher-than-expected number of positive screening results.
Laboratory professionals launched an immediate review, which ultimately led to the discovery of the fault.
Health districts affected by the incident were informed, and efforts began to contact potentially impacted patients and offer them repeat testing.
The case has sparked concern among patient groups.
The association El Defensor del Paciente has asked Malaga’s chief prosecutor to investigate the incident and determine whether formal proceedings should be opened over the false positive results.
Colon cancer is one of the most common cancers diagnosed in Spain, and screening programmes rely heavily on early detection through stool testing before patients are referred for further examinations such as colonoscopies.
Health officials insist the malfunction did not result in missed cancer diagnoses, but acknowledge that it may have caused significant anxiety for patients who were incorrectly informed that their initial screening test was positive.
Read more Andalucia news at the Spanish Eye.
