Between the last meal and the blood draw, at least eight hours must elapse for two reasons. The first seems logical: after eating food, the concentration of some parameters that are measured in analytics, such as cholesterol, glucose, triglycerides and transaminases, can change. In fact, after eating fat, lipids can be seen in plasma , because they stain it yellow.
And although some studies indicate that the incidence in these values is minimal if a normal breakfast is eaten, it is better to avoid any possibility of biochemical alteration . It is also recommended to extend the fast to fourteen hours if the patient previously has high triglyceride levels.
The second reason is perhaps less obvious and has to do with the technology used to analyze the sample: the equipment is designed to handle clean blood , and the blood that passes through the body after ingestion is not, as it contains substances in suspension. that could interfere with the operation of the appliance and the results.
The same is not the case with urinalysis ; taking the sample on an empty stomach does not alter the presence or not, for example, of the microorganisms responsible for the infections. The first thing in the morning is collected because it is the most concentrated and contains the waste products that the kidneys have produced during the night.
Another tip from doctors is to let the urine flow a little before collecting it, because the presence of bacteria is greater as urination progresses .
