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Five Major Considerations For Sputum Culture
Nov 23, 2018


1. Specimen collection and inspection

Generally, it is better to take the sputum before the meal in the morning. The specific method is to thoroughly clean the mouth first. You can rinse your mouth with water. If you have a denture, you should take it off and then cough hard. Try to cough up the deep sputum and directly spit it into the special. In the sputum collector, ensure that the container is sterile, sealed and dry before use. After the sputum is collected, it should be tightened and immediately sent for inspection. It should be no more than 2 hours at room temperature. If it is unconditionally sent, it should be stored in a refrigerator at 4 °C. Stored within and processed within 24 hours. Non-hospital patients should be aware that they should be fasted for 1 hour before taking sputum to avoid contamination of sputum with oral food residues. Note that as much as possible to remove sputum, at least 1ml. In order to dilute sputum, patients can be advised to drink plenty of water on the night before the examination, if necessary, atomization treatment can make sputum easy to discharge. For patients with endotracheal intubation, the deep sputum of the airway should be aspirated in a sterile suction tube. For acute infections, usually only one time, but suspected fungi, mycobacteria, Pneumocystis carinii infection or changes in the condition should be sent to the morning sputum for three consecutive times.

2. Determine whether the specimen is qualified

The naked eye, the specimen is saliva-like or watery, and the positive rate of the specimen is low. Sputum smear, observed under low magnification, white blood cells: squamous epithelial cells <2.5:1, and Peking Union Medical College Hospital "medical diagnosis and treatment routine" proposed no matter the number of multinucleated neutrophils, if the number of squamous epithelial cells >10 / Low magnification is unqualified, that is, the specimen is considered to contaminate the normal flora of the oropharynx, and it is recommended to re-collect.

3. Separation and culture

Commonly used media are blood plates, chocolate agar, and MacConkey agar. The blood plate is mainly used for the growth of G+ cocci and G-bacillus such as Streptococcus pneumoniae and hemolytic streptococcus, especially for the evaluation of colony morphology; chocolate agar is suitable for isolating bacteria with harsh culture conditions such as Haemophilus; Malcon agar is suitable for G - Bacilli and further distinguish between lactose positive and lactose negative pathogens.

4. The results of interpretation

The results of sputum culture are usually reported in semi-quantitative manner. The dominant bacteria in the qualified sputum specimens are moderately grown (+++), or a small amount of growth in the qualified sputum specimens, but consistent with the sputum smear results, or multiple times in three consecutive days. The sputum cultures are all the same kind of bacteria. In addition, when the sputum smear microscopy found typical pathogens, but the sputum culture was negative, we also think it has reference significance.

5. Drug susceptibility results

Antibiotic susceptibility test results can be divided into sensitive (S) mediation (I) and drug resistance (R), S means that the conventional dose is effective, I suggest that the drug dose needs to be increased to reach a higher blood drug concentration, and R means that the antibiotic is invalid. . However, it should be noted that the results of drug susceptibility should be combined with clinical practice. The actual effect should be based on the application of antibiotics. Because laboratory diagnosis can also have “false sensitivity” or “false resistance”, it is not necessarily “sensitive”. It is not true pathogenic bacteria that may be cultivated. It is also related to factors such as drug dosage form and bioavailability. It needs to be identified by clinicians based on personal experience.