Although the Manchester Triage System (MTS) is widely used and validated internationally, it has some limitations. Its accuracy is moderate, especially for children and the elderly. Rising patient numbers and overcrowded emergency departments increase wait times, sometimes beyond safe limits. In Slovenia, MTS has been in use for 14 years without major updates, despite a significant rise in emergency visits. The yellow triage category (60-minute wait time) includes a very diverse group of patients, some of whom might require faster care. Older patients, in particular, often show atypical symptoms and may be under-triaged. Including rapid bedside lab tests, like blood lactate levels, could improve risk assessment and triage accuracy. Elevated lactate is linked with higher mortality and can help identify critically ill patients more effectively. The proposed study is a prospective, randomized trial involving two groups of patients in the yellow triage category, all of whom will have their capillary blood lactate levels measured. Patients with normal lactate levels will be excluded. Only patients with elevated lactate will be compared. The test group will be re-triaged to the orange category and treated more urgently. The control group, despite also having high lactate levels, will remain in the yellow category, and their elevated lactate values will not be shared with the treating physician. Randomization will be based on the patient's birth date (even days = test group, odd days = control group). Only the nurse will know the result, maintaining physician blinding to avoid the Hawthorne effect-changes in behavior due to awareness of being studied. Standard lab tests will be performed later during treatment as deemed necessary by the attending doctor.

Inclusion Criteria:

• signed consent, yellow MTS triage category

Exclusion Criteria:

• pregnant women, trauma patients, epileptic seizures, adrenergic therapy in prehospital unit

Individual participant data will not be shared with other researchers. The decision not to share IPD is based on privacy concerns, data protection regulations, and institutional policy.