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Collection and preservation of IVD test samples

Collection and preservation of IVD test samples

  • Time of issue:2023-04-03
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(Summary description)

Collection and preservation of IVD test samples

(Summary description)

  • Categories:Blogs
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  • Time of issue:2023-04-03 16:27
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Information

Common specimens for clinical testing generally include blood (finger blood, venous blood), urine, stool, cerebrospinal fluid, thoracic and ascitic fluid, prostate fluid, semen, vaginal secretions, etc. The time, method and preservation of these specimens are subject to certain requirements.

 


Ⅰ. Blood specimens


Some physiological factors, such as smoking, eating, exercise, mood swings, pregnancy, body position, etc. can affect the changes of certain components in blood, and some even have diurnal changes. Therefore, the collection of blood specimens should avoid the interference of physiological factors as much as possible, and it is appropriate to have consistent conditions, and if it cannot be avoided, the factor should be indicated on the specimen.


1. Peripheral blood


Generally, the blood is collected from the inside of the ring finger of the left hand, which should be free from frostbite, inflammation, edema and breakage. If the site does not meet the requirements, other finger sites are used instead. For patients with burns, blood can be collected from intact skin. Since some routine blood tests (such as white blood cell count, classification, etc.) fluctuate too much due to physiological factors, it is advisable to make the conditions as consistent as possible when comparing.


Testing items involving in vivo bleeding and clotting functions (such as platelet count, bleeding time or clotting time, etc.) must pay attention to understanding whether the patient has used anticoagulant and pro-coagulant drugs in order to reduce or avoid the influence of interfering factors.


2. Venous blood


In addition to the various hemostasis and thrombosis detection projects involving the use of anticoagulated venous blood plasma, the vast majority of the current test items can be analyzed directly using venous blood serum. In the serum test items, some (such as blood glucose, lipids, etc.) by diet and diurnal factors, generally early morning fasting blood specimens are appropriate;


Some of them decay faster in the blood (serum enzyme activity determination such as ACP activity, etc.), and their storage activity decreases differently from 0 to 4°C. The testing of these items must be timely and rapid; some (such as creatine kinase, etc.) are more affected by factors such as exercise. It is also important to avoid hemolysis when drawing blood, especially when it comes to the determination of blood potassium and LDH.

 


Ⅱ. Urine specimens


Like blood specimens, urine specimens are affected by factors such as diet, exercise, and the amount of medication, especially diet, so morning urine is generally preferred to random urine. Morning urine is the first urine specimen after waking up in the morning, which is more concentrated and acidified, and has a relatively high concentration of formed fractions (e.g., blood cells, epithelial cells, tubular forms) for easy observation.


Random urine is a random urine, which is convenient to retain, but is more affected by diet, exercise, and drugs, and is prone to false positive and false negative results, such as dietary proteinuria, dietary diabetes, and vitamin C interference with occult blood results. Postprandial urine (urine collected from patients 2 hours after lunch) is suitable for the examination of urine sugar, urine protein and urine bilirubin, and the urine specimen at this time can increase the sensitivity of the test and detect minor lesions.


A 12-hour urine cell count, or Addis count (all urine from 8 p.m. the previous evening after bladder emptying to 8 a.m. the next morning), must include the preservative formaldehyde because of the prolonged period of time and the tendency for bacteria to multiply. 24-hour urine (all urine from 8 a.m. the first morning after bladder emptying to 8 a.m. the next morning) is used to quantify chemicals, including protein, sugar, urinary 17-ketones, 17-hydroxysteroids, catecholamines, and Ca2+. Ca2+, etc. Different substances are detected and different preservatives are selected for antisepsis.


Clean middle urine is mostly used for urine bacterial culture, which requires sterility, and the specimen is retained after rinsing the vulva. All urine specimens should be collected in sufficient quantity, at least 12 ml, preferably 50 ml, and all urine should be collected at regular intervals.

 


Ⅲ. Stool specimens


Stool specimens have an important reference value for determining digestive system diseases. The collection requires the use of clean bamboo sticks to select the stool containing mucus, pus and blood and other abnormal lesion components, and the stool without abnormal appearance must be taken from the surface, depth and the end of the stool in many places. Look for parasitic worms and egg count should be collected 24 hours stool. Dysentery amebic trophozoites should be examined immediately after defecation, and the material should be taken from the pus and blood and thin and soft places, and sent for examination with heat preservation.


When checking for Schistosoma japonicum eggs, mucus and pus and blood should be taken, and at least 30 g of stool should be taken when hatching trichurias, and should be processed as soon as possible. To examine pinworm eggs, a transparent film swab should be used at 12 pm or early in the morning before defecation to swab from the perianal folds and immediately microscopic examination.


For the occult blood test (chemical method), meat and food containing animal blood and iron and vitamin C are prohibited for 3 days before the test. All stool specimens should be examined within 1 hour after collection to prevent the destruction of organic fractions by digestive enzymes and pH.

 


Ⅳ. Cerebrospinal fluid specimens


Cerebrospinal fluid specimens are sent for examination immediately after collection, leaving it too long will affect the test results: such as cell denaturation, destruction, resulting in inaccurate counting and classification; some chemicals such as glucose will reduce the content of decomposition; bacterial autolysis affects the detection rate of bacteria.


Cerebrospinal fluid is usually divided into three sterile tubes after extraction, the first tube for bacterial culture, the second tube for chemical analysis and immunological examination, and the third tube for general traits and microscopic examination, the order of the three tubes should not be reversed. Because the specimen collection is difficult, all the delivery and detection process should pay attention to safety.

 


V. Thoracoabdominal fluid specimens


As with cerebrospinal fluid specimens, the specimens collected should be safe and sent for examination in a timely manner. Generally also divided into three tubes, a tube for routine cytological examination, a tube of biochemical examination, a tube of bacterial culture, the order is the same as the cerebrospinal fluid is appropriate.

 


Ⅵ. Prostate fluid specimens


Prostate fluid specimens are collected from the prostate gland after massage, and when the amount of fluid is small, it is directly dropped on the slide and sent for examination in time, care must be taken to prevent the specimen from steaming dry, and when the amount is large, it is collected in a clean and dry test tube. If the prostate fluid is not massaged, the urine sediment after the massage can be examined.

 


Ⅶ. Semen specimens


Semen specimens should be collected before abstinence for 3~7 days, and after the urine is drained, masturbation method or other methods can be used to drain the semen directly into a clean container, keep it warm and send it for examination in time. Since sperm production varies greatly from day to day, it should generally be examined 2~3 times (each time with an interval of 1~2 weeks) before making a diagnosis.

 


VIII. Vaginal secretion specimen


The collection of vaginal specimens should be prohibited 24 hours prior to intercourse, bathing, vaginal examination, vaginal irrigation and local medication, etc. The instruments used for sampling should be clean. Generally, a saline-soaked cotton swab should be used to collect the specimen from the deep part of the vagina or the posterior part of the vaginal vault or the cervical canal, and a saline smear should be made to observe the vaginal secretion specimen.

 

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