Final answer:
Hematologic samples should be examined within one hour of collection to ensure the accuracy of blood analyses, such as Blood Culture. The separation of serum for analysis, which can naturally occur within an hour in an untreated tube, is an important step in sample preparation. Timely separation of serum or plasma is essential to prevent changes in the sample that could affect test results.
Step-by-step explanation:
Hematologic samples, including blood samples, are best examined as soon as possible after collection. However, if the laboratory analysis is to be accurate, they should be examined within a certain time frame. Different tests may require different processing times. For Blood Culture purposes, for example, the sample should be examined as soon as possible ideally within one hour to ensure the best growth and detection of bacteria or fungi. However, a blood sample in a glass tube seems to be undergoing a coagulation process when not treated with anticoagulants, allowing serum to separate naturally from the clotted cellular components which takes about an hour. During this time, the blood cells clot and the serum is separated. The serum is the liquid that can be harvested after the blood has clotted and the cellular components have been removed, which contains electrolytes, antibodies, antigens, hormones, and any exogenous substances like drugs. Separation of plasma or serum needs to be done promptly after sampling (typically within one to two hours) to prevent cellular metabolism from altering the levels of plasma constituents.
In cases where hematopoietic stem cells are being isolated from the patient's blood sample, this process can often be done within a few hours, followed by growth in culture with appropriate hemopoietic growth factors. Samples for other types of analyses such as pharmacokinetic studies in animals may be pooled and collected over a longer period, up to 24 hours, to assess the compound's behavior over time.