A well formatted Lab Report duly signed and sealed by a Pathology Doctor itself is a bonafide document, as it contains not only detailes of tests carried out and its results, but also information about the consultant doctor and his diagnosis about the patient, apart from patient's details and treatment starting date. Thus, it can be taken as a valid document.
Anyhow, on resuming duty, after sick leve/treatment, person has to produce a medical fitness certificate also.