Does green phlegm mean I need antibiotics?

One of the most common presentations we hear, particularly as we enter the autumn with schools going back to share the viruses that have been brought back from far-flung summer holidays with the wider population, is “I have this cough and I’m bringing up green phlegm so I think I need some antibiotics”.

A fair question, because we used to place great importance on colour, quantity and consistency of phlegm. Unfortunately nowadays, symptoms alone often can’t give a reliable answer as to whether antibiotics are required, but we at Lisle Medical have a simple way of being more sure.

Viral and bacterial respiratory infections can both cause cough, fever, tiredness, breathlessness and phlegm. Even yellow or green phlegm doesn’t necessarily mean an infection is bacterial. The colour is largely caused by inflammatory cells involved in the body’s response to infection and, by itself, isn’t a good reason to prescribe antibiotics.

How do we decide whether antibiotics are needed?

The first step is a proper clinical assessment.

We consider how long you have been unwell, whether you are improving or deteriorating, your temperature, pulse, breathing rate and oxygen saturation, as well as your age and medical history. Listening to the chest can identify features that increase or reduce our suspicion of pneumonia.

Often, that gives us a reasonably clear answer. Sometimes, however, there is a genuine grey area: you are clearly unwell with a respiratory infection, but it isn’t obvious whether antibiotics are likely to help.

This is where a point-of-care CRP test can be particularly useful.

A CRP result during your appointment

At Lisle Medical, we have a point-of-care CRP analyser in each clinic and one for home visiting, allowing us to measure C-reactive protein from a small blood sample during the consultation.

CRP is a marker of inflammation. It isn’t simply a test for “viral versus bacterial” infection, but when interpreted alongside your symptoms, observations and examination, it can provide valuable additional evidence when deciding whether antibiotics are appropriate.

Crucially, because we can perform the test in the clinic from a tiny amount of blood obtained with just a small pinprick, we don’t have to send the sample to a laboratory and wait for the result. The result can inform the decision during the same appointment, within 3 minutes.

Current NICE guidance for adults with a suspected lower respiratory tract infection recommends considering point-of-care CRP testing in addition to taking a full history and thorough examination.

Why avoiding unnecessary antibiotics matters

Most people know this already as the medical profession have been banging this drum for a while now. Antibiotics are extremely useful when they are needed, particularly for significant bacterial infections such as pneumonia. But they don’t treat viral infections and generally provide little benefit for an uncomplicated viral cough or bronchitis.

Taking antibiotics unnecessarily exposes you to potential side effects and contributes to antimicrobial resistance.

Equally, we don’t want to withhold antibiotics from someone who is likely to benefit from them.

Point-of-care CRP testing helps us make that decision using additional objective information rather than relying on the colour of your phlegm or prescribing antibiotics “just in case”.

When should you see a doctor about a chest infection?

Most uncomplicated coughs and respiratory infections improve without antibiotics. You should seek medical advice if you are becoming increasingly unwell rather than gradually improving, have significant breathlessness, persistent or high fever, chest pain, cough up blood, or have low oxygen levels.

There should also be a lower threshold for assessment if you are older, pregnant, immunosuppressed, or have significant heart or lung disease.

At Lisle Medical, we can assess respiratory infections with a clinical examination, oxygen saturation and other observations, with point-of-care CRP testing available when it can help clarify whether antibiotic treatment is appropriate.

The aim isn’t simply to prescribe fewer antibiotics. It’s to make a better-informed decision about when antibiotics are likely to help – and when they aren’t.