Sooner or later, everyone will end up getting their blood tested. It doesn’t matter if it is to determine your health condition or maybe because you will donate blood to someone; you will usually never know what they do with your blood once they have it in the test tube, but here is the secret.
The blood analysis consists of extracting a small amount of blood from the patient’s circulatory system using blood culture kits for laboratories, which will later be preserved in inappropriate media and taken to be analyzed in a laboratory specialized in this type of study.
The blood sample for blood culture should be taken from a vein, generally from the forearm. The use of arterial blood has not shown advantages over venous blood. The collection should not be performed through intravenous or intra-arterial catheters, except in cases of suspected catheter-associated bacteremia. Each blood sample should be obtained from different venipuncture sites.
The main problem for the correct interpretation of blood cultures is their contamination with skin microbiota during collection. To avoid this, the skin at the site of collection should be thoroughly prepared beforehand. The blood culture kits for laboratories should be kept at hand so that after palpation of the vein chosen for the puncture, the area should be cleaned with 70º isopropyl or ethyl alcohol for 30 seconds. Then apply an iodine solution (1-2% tincture of iodine for 30 seconds or 10% povidone-iodine for 1 minute) covering a circular area of 2-4 cm in diameter.
It is essential to let the iodine compound dry so that it can exert its oxidizing action and avoid touching the venipuncture site with the fingers and talking or coughing while the extraction is being performed. With the proper aseptic technique, the number of contaminated blood cultures should not exceed 3%. Before proceeding with the extraction, the caps of the venipuncture bottles should be cleaned.
The stoppers of the blood culture bottles supplied in the blood culture kits for laboratories should be cleaned with an antiseptic and allowed to dry to prevent them from entering the inside of the bottle when inoculating the blood.
The needle is then inserted into the chosen vein, and the volume of blood is withdrawn without using an anticoagulant. Absorbent cotton or other non-sterile material should not be placed over the needle when removed from the vein. Blood culture vials from the blood culture kits for laboratories should be inoculated quickly to avoid clotting blood in the syringe by drawing the needle vertically through the vial.
The anaerobic bottle should be inoculated first, avoiding air entry, followed by the aerobic bottle, inverting them several times to mix the blood and the culture medium.
Each blood culture or extraction (two bottles) with the inoculated blood should be duly identified with the patient’s data(medical history number, name, and surname, service, floor, bed number), as well as the name of the physician requesting it, the patient’s diagnosis, the antimicrobial treatment he/she is receiving and the type of analysis required (conventional blood culture or for slow-growing microorganisms). The telephone number of the nursing control in which the patient is admitted should also be recorded so that the preliminary results of the blood cultures can be reported in case of positivity. If the blood cultures are taken in the Emergency Department and the patient is discharged, the telephone number where the patient can be reached should be noted in case of blood culture positivity.
The bottles of blood culture kits for laboratories, with proper identification, should be transported to the laboratory immediately. They should only be kept at room temperature for short periods not to affect the subsequent recovery of the microorganisms. If they cannot be sent directly to the laboratory, they should be incubated in an oven at 35-37ºC until that time. Blood cultures that are to be processed in automated systems can be kept at room temperature or 35-37ºC. Blood cultures should never be refrigerated.
As soon as the blood cultures are received in the laboratory, and before being introduced into the automatic machines, then blood cultures should be carefully examined to check that they can be handled safely, that they are intact, without breaks or cracks, that their identification is correct, that the volume of blood is adequate and to detect macroscopically signs of growth. If the latter is absent, the vials of the blood culture kits for laboratories will be quickly introduced into the automatic devices to avoid delaying the development of the microorganisms.
Blood analysis is one of the most basic, practical, and commonly used tools in medicine because the extraction technique is relatively simple. The study of the sample by specialized laboratories provides valuable information about the health status of the person. It allows knowing a person’s blood group, knowing if a woman is pregnant and the time of her pregnancy, and ruling out and diagnosing multiple systemic pathologies such as diabetes, dyslipidemia, renal diseases, metabolic diseases, infectious processes, etcetera.
