Full Blood Count (FBC) in acute appendicitis


A 19-year-old female presented to the emergency department (ED) with a 3-hour history of right iliac fossa (RIF) abdominal pain and a low-grade fever.

A urinalysis performed confirmed no pregnancy, however it was suggestive of a urinary tract infection (++ leukocytes, ++ nitrites, ++ blood), despite no dysuria or increased urinary frequency. Analgesia was provided parentally and reassessment revealed pain over McBurney’s point, a positive Rovsing’s test and guarding of the RIF. FBC returned showing a raised white cell count (WCC) and neutrophilia. The patient was referred to the surgical team and this case prompted an examination of the role of the FBC in the diagnosis of appendicitis.

So what?

The diagnosis of acute appendicitis is essentially based upon a history and clinical findings, although a FBC sample should be taken for all suspected cases (Wyatt et al 2012, Longmore et al 2014).

A study by Birchley (2006) examined the relationship between leukocytosis and neutrophilia on the likelihood of finding acute appendicitis during surgery (when a clinical diagnosis had been made). The sensitivity and specificity data is shown in table 1. His findings demonstrated a positive likelihood ratio of 2.34 and 2.01 for leukocytosis and neutrophilia respectively (Birchley 2006). However he also found a negative post-test probability of 50% for both tests, meaning the probability of having a normal appendix with a normal result is essentially no more accurate than a coin toss (Birchley 2006).

Table 1 – The diagnostic attributes of tests for determining normal from abnormal appendices (Birchley 2006).

Test Sensitivity Specificity PPV* NPV* Likelihood ratio (+’ve) Likelihood ratio (-‘ve)
WCC 0.78 0.67 0.89 0.48 2.34 0.33
NC 0.86 0.57 0.88 0.53 2.01 0.24
WCC + NC 0.85 0.62 0.89 0.53 2.20 0.25

*PPV = Positive Predictive Value, NPV = Negative Predictive Value.

Now what?

In the ED an initial diagnosis of acute appendicitis should be based upon history and clinical examination. A FBC demonstrating leukocytosis and neutrophilia may support the diagnosis, but normal inflammatory markers will not be able to exclude it.


 Rob Fenwick


Birchley, D. (2006) Patients with clinical acute appendicitis should have pre-operative full blood count and C-reactive protein assays. Annals of the Royal College of Surgeons of England. Volume 88, pp 27-32.

Driscoll, J. (2007) Practicing clinical supervision: a reflective approach for healthcare professionals (2nd edition). Elsevier. Edinburgh.

Longmore, M., Wilkinson, I. B., Baldwin, A & Wallin, E. (2014) Oxford handbook of clinical medicine (9th edition). Oxford University press. Oxford.

Wyatt, J., Illingworth, R., Graham, C & Hogg, K. (2012) Oxford handbook of emergency medicine (4th edition). Oxford University press. Oxford.

4 thoughts on “Full Blood Count (FBC) in acute appendicitis

  1. nicole says:

    You mean leukocytosis, not leukopenia, right?

  2. rob fenwick says:

    Absolutely! Thanks

  3. Lunik says:

    What about the reliability of Alvarado score in ED settings?

  4. rob fenwick says:

    We have a blog post on “clinical decision rules in appendicitis” being released in the next few weeks! – Watch this space!

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