Practitioners and patients alike often assume that discolored sputum or discharge is a definite indication of bacterial infection and the need for antibiotics. This assumption is worth testing because, as reported in the previous post, antibiotics given when a respiratory infection is viral impair the immune response. In a study published in the Scandinavian Journal of Primary Health Care the authors look into the matter:

“Sputum colour plays an important role in the disease concepts for acute cough, both in the patients’ and the doctors’ view. However, it is unclear whether the sputum colour can be used for diagnosis of a bacterial infection.”

They obtained sputum samples from 241 patients suffering from acute cough drawn from 42 general practices in Düsseldorf, Germany. They examined the relation of sputum color and microbiological proof of bacterial infection by positive culture and the presence of white blood cells. The correlation was not clear-cut:

“In 28 samples (12%) a bacterial infection was proven. Yellowish or greenish colour of the sputum sample and bacterial infection showed a significant correlation. The sensitivity of yellowish or greenish sputum used as a test for a bacterial infection was 0.79; the specificity was 0.46. The positive likelihood-ratio (+LR) was 1.46.”

In other words, only a 46% likelihood that yellow or green sputum would indicate a bacterial infection. Thus they concluded:

“The sputum colour of patients with acute cough and no underlying chronic lung disease does not imply therapeutic consequences such as prescription of antibiotics.“

Another study just published in the European Respiratory Journal offers further evidence that discolored sputum cannot be assumed to indicate the need for antibiotics. The authors state:

“We investigated whether discoloured sputum and feeling unwell is associated with antibiotic prescribing and benefit from antibiotic treatment for acute cough/lower respiratory tract infection in a prospective study of 3402 adults in 13 countries.”

The authors investigated the association between producing discoloured sputum and an antibiotic prescription and then the association between an antibiotic prescription and symptom resolution. What did their data show?

“Patients producing discoloured sputum were prescribed antibiotics more frequently than those not producing sputum, unlike those producing clear/white sputum. Antibiotic prescribing was not associated with greater rate or magnitude of symptoms score resolution (as measured by 13 item scale completed by patients each day) among those who: produced yellow or green sputum…”

The authors’ conclusion, along with the detrimental effects of the improper use of antibiotics, should be kept in mind:

“Adults with acute cough/LRTI [lower respiratory tract infection] presenting in primary care with discoloured sputum were prescribed antibiotics more often compared to those not producing sputum. Sputum colour, alone or together with feeling generally unwell was not associated with recovery or benefit from antibiotic treatment.“

While yellow or green sputum should not be accepted as sole justification for the use of antibiotics, a study published in the journal Respiratory Care establishes that cream, white or clear sputum is almost guaranteed not to be a bacterial infection. The authors set out to…

“…determine whether the simple characteristic of sputum color provides information that impacts resource utilization such as laboratory testing and prescription of antibiotics.”

They correlated out-patient sputum samples assigned to 8 color categories (green, yellow-green, rust, yellow, red, cream, white, and clear) gram stain and culture results. Their findings for discolored sputum were similar to the other studies:

“Of 289 consecutive samples, 144 (50%) met standard Gram-stain criteria for being acceptable lower-respiratory-tract specimens. In the acceptable Gram-stain group, 60 samples had a predominant organism on Gram stain, and the culture yielded a consistent result in 42 samples (15% of the 289 total specimens). Yield at each level of analysis differed greatly by color. The yield from sputum colors green, yellow-green, yellow, and rust was much higher than the yield from cream, white, or clear.”

Based on their data they offer a clear statement in their conclusion:

“If out-patient sputum is cream, white, or clear, the yield from bacteriologic analysis is extremely low. This information can reduce laboratory processing costs and help minimize unnecessary antibiotic prescription.”

It should be noted that these studies concern mainly respiratory infections in an out-patient setting and not severe COPD or cystic fibrosis. Whether antibiotics are indicated or not should be determined by a skilled comprehensive assessment, not by sputum color alone.