Researchers studied whether complete blood cell count (CBC) tests are accurate in identifying invasive bacterial infections in babies under two months old.
Babies with fevers are often seen in hospital emergency departments to check whether they have serious bacterial infections such as urinary tract infection, bacteremia (blood infection), or bacterial meningitis (infection of the membranes around the brain). While urine tests are very accurate in diagnosing urinary tract infections, it is more difficult to confirm bacteremia and bacterial meningitis, known as invasive bacterial infections.
A blood test called a complete blood cell count (CBC) is the most commonly used test in the emergency department. This test looks at the number and type of different cells circulating in the blood such as white blood cells, neutrophils, red blood cells, and platelets. A CBC test can give an indication of infection or disease. For example, white blood cells and neutrophils are usually increased during infection. However, some studies have suggested that CBCs are not accurate indicators of which infants have invasive bacterial infections.
Other tests such as blood culture tests or spinal fluid tests can confirm infection and give more detail about the type of bacteria and what antibiotics may be used, but these tests take longer to analyze. Newer tests looking for other signs of infection such as C-reactive protein have been shown to accurately predict which young infants have invasive bacterial infections, but these are not widely available. This means that treatment might need to be decided on the results of the CBC tests.Researchers at Baylor College Texas (USA)performed a large study to investigate the accuracy of CBCs in predicting invasive bacterial infections in young babies. They recently reported their findings in JAMA Pediatrics.
The study included previously healthy babies up to 60 days old attending 26 emergency departments with a fever of 38°C or higher between 2008 and 2013. As well as CBC tests, the babies included in the study had blood culture tests and either a cerebrospinal fluid test or information from a follow-up appointment at seven days.
Over 4,300 infants were included in the analysis. A total of 97 babies (2.2%) had invasive bacterial infections, of which 73 had bacteremia and 24 had bacterial meningitis confirmed on blood cultures or cerebrospinal fluid tests. None of the CBC test components reliably distinguished between babies with or without invasive bacterial infections. Although the children with invasive bacterial infections had higher white blood cell and neutrophil counts and lower platelet counts there was no blood count level at which invasive bacterial infections could be reliably predicted.
One possible explanation for the CBC test’s poor performance changes in the type of bacteria causing invasive bacterial infections in young infants. Since the use of vaccines for pneumococcus – previously a common cause of infection in young babies – the bacteria now causing infections may produce less of an inflammatory response in the blood. Another reason may be that parents have become more anxious about fever and bring children to the emergency department at an early stage, before signs of infection are seen in the CBC.
The researchers suggest that it is time to look for better diagnostic tests and to incorporate other available diagnostic tests more routinely into their practice.This could improve decisions about appropriate treatment of babies with fever attending the emergency department who may or may not have invasive bacterial infections.
Written by Julie McShane, Medical Writer
Cruz AT, Mahajan P, Bonsu BK, et al. Accuracy of complete blood cell counts to identify febrile infants 60 days or younger with invasive bacterial infections. JAMA Pediatrics Published online Sept 11, 2017. Doi:10.1001/jamapediatrics.2017.2927.