Biochemical specimens have been collection since long to perform variety of tests. New technologies employed allow wide range of sample collection for the human body. Though, blood samples are the most used in biochemical testing, samples of saliva, urine, semen, body fluid and tissues are also in common use.
Some of the biochemical can be testing from more than one biological sample. For example, glucose can be tested by both blood and urine samples. However, choice of biological sample is based on the the purpose of a diagnosis of diabetes while urine sample testing monitor blood glucose fluctuation in diabetics.
There are WHO guideline that must be followed while collecting and handling biological samples. They are not only source of various infectious microorganism but are sensitive to various laboratory conditions such as temperature, freeze/thaw cycle and time lapse between collection and analysis.
a) Blood collection
Blood samples should be collected by the trained professional or phlebotomist so that the quality and quantity is not compromised. A vacutainer blood collection tube made up of glass or plastic is commonly used to collect the sample. Blood should be fractioned before analysis and storage.
Depending upon the nature of analysis, samples should be collected in different tubes. There are two types of blood collection tubes with color-coded stoppers.
Most of the blood collection tubes are coated with an additive that either accelerates blood clothing (clot activator) or prevents the blood from clothing (anticoagulant). Purple cap also called EDTA tube contains anticoagulants such as ACD, heparin, and EDTA.
These tubes are generally used when whole blood is needed for the analysis i.e. completer blood count (CBC) test. Moreover, due to presence or anticoagulant ,plasma is produced after centrifugation of blood in such tubes. Another type is of red cap commonly known as serum tube contains a clot activator and yield serum sample when the blood is separated by centrifugation.
To reduce contamination, serum should be separated from other blood components as soon as possible. The serum is used to analyses nutrients, proteins(antibodies) and lipids. Depending upon the nature of the analysis, both serum and plasma specimens could be used for protein analysis.
For prolonged study, plasma is a better specimen as blood coagulation results in losses of protein. There is no fixed time between blood collection and further processing.
RNA and protein require a special procedure to maintain their integrity during collection and processing. For example, RNase inhibitors are added to preserve RNA integrity.
B) Urine collective
A urine sample can be collected at different times depending on the analytical goal. For detection of analytes in laboratory assays, a morning urine sample is recommended while random sapling is appropriate for drug and cytology studies.
However, fractional specimens where the participant are required to fast after evening meal before the urine is collected in second morning are utilized to compare urinary analyte levels with the blood concentration.
Timed urinary collection where urine sample is collected over a specified period of time; for a shorter collection of 2 hours and longer collection ranging from 12 to 24 hour, is performed to compare the excretion pattern .
Different collection vessels, ranging from 50-3000ml are generally used. Preservatives are used depending upon analyte methodology, time delay, and transport conditions. The most used preservatives in urine sampling are sodium metabisulfite and EDTA.
C) Sputum collection;
Sputum is generally collected to assess any infection of lungs or airways. Patients are required to cough up sputum as far down from the lungs as possible. The best time to accomplish it is the morning before eating or drinking anything, by taking several deep breaths before expectorating into a collection cup. The sputum should be thick but watery as seen during saliva production.
D) Saliva collection:
It is an important and suitable specimen as an invasive diagnostic tool. It has been used for diagnosis of autoimmune diseases, diabetes, CVDs, dental caries and oral diseases. Saliva with exfoliated buccal cells is an excellent source of DNA for genetic studies. Self- collection of saliva is a safe, convenient and cost effective.
Several methods have been developed including swabs, mouthwash, and cytobrushes. However, mouthwash protocol is used largely as it yields DNA of good quality and quantity. Newer methods of saliva collection employ or agene collection tubes which contain kit's proprietary reagents'' that inactivate salivary enzymes and minimize biochemical hydrolysis of DNA.
Such reagents also prevent the growth of bacteria in the saliva thus preserving DNA for longer duration.
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