Bilirubin; a diagnostic marker for appendicitis - ScienceDirect
1. Introduction
In the continued absence of a 100% accurate test for appendicitis, any investigation that can contribute to its diagnosis is valuable. Appendicitis remains the most common abdominal surgical emergency, with an incidence between 55.3 (females) and 68.8 (males) to 88 per 100, 000.1, 2 A variety of conditions can cause right iliac fossa (RIF) pain, which do not require surgery. When the diagnosis is not clear, further investigations may include ultrasound, CT scan or diagnostic laparoscopy. A negative appendicectomy from an incorrect diagnosis incurs the costs and potential complications from an unnecessary operation.
Previous retrospective studies have all shown evidence confirming the high specificity of hyperbilirubinaemia for perforated appendicitis3, 4, 5, 6, 7; when bilirubin is raised, the likelihood of appendicitis was between 0.7 and 0.87. Two prospective studies have equivocal8 and positive results.9 Overall, this research has suggested that hyperbilirubinaemia may be a better predictive marker for perforated appendicitis than white blood cell (WBC) or C-reactive protein (CRP) levels. Some studies have also demonstrated an association between hyperbilirubinaemia and simple appendicitis.6 Simple appendicitis can be difficult to differentiate from other causes of RIF pain that do not require surgery; these conditions include mesenteric adenitis in children, benign gynaecological disease such as ovarian cysts, mittelschmerz or pelvic inflammatory disease in women, or inflammatory bowel disease in young adults.
Liver function tests (LFTs) are a commonly requested blood test. Unlike imaging modalities, they are relatively inexpensive, and carry no risks such as irradiation from CT scans or surgical complications from laparoscopy. A safe, cheap, rapid, widely available, accurate diagnostic marker for appendicitis would be useful to the emergency general surgeon to manage suspected appendicitis.
2. Aims
This study seeks to investigate whether there is a statistically significant association between hyperbilirubinaemia and appendicitis (simple or perforated). By carrying out a prospective study including patients admitted with RIF pain, we also will investigate the diagnostic value of bilirubin in differentiating appendicitis from RIF pain of other causes.
Our secondary outcomes will investigate whether there is an association between hyperbilirubinaemia and perforated appendicitis, and whether bilirubin is a more specific marker than WBC or CRP for appendicitis (simple or perforated).
3. Methods
Our prospective, observational study took place in a district general hospital in the UK from the 1st of January 2012 until 18th July 2012.
All patients admitted under the general surgeons with RIF pain with LFTs recorded on admission were eligible for inclusion. LFTs are included routinely on nearly all blood tests performed on surgical patients with abdominal pain. Our exclusion criteria were a history of liver or haemolytic disease that could lead to deranged LFTs (hepatitis of any aetiology, Gilbert's disease, Dubin–Johnson syndrome, benign recurrent intra-hepatic cholestasis or alcoholism). Patients seen with RIF pain who were discharged after review in the emergency department were not included.
As part of a registered trust audit, data was collected prospectively. Ethics approval was not required for audit purposes, and as patient care was routine, no additional tests were performed. The variables analysed included:
- 1.
Age, sex, time/date of admission.
- 2.
LFTs (liver function tests, including bilirubin), WBC and CRP on admission, with time and date recorded.
- 3.
Date of operation and operative findings (time between blood tests and surgery not recorded).
- 4.
The histology of their appendix if removed.
At operation, trust policy is to remove all appendices if an open procedure was performed. During diagnostic laparoscopy, the appendix is removed if it is inflamed, or if it is normal and no other pathology is seen to exclude microscopic appendicitis.
Hyperbilirubinaemia was classified as bilirubin levels above 20 μmol/L, approximately the common upper limit (20.5 μmol/L) of the normal range in most UK pathology laboratories. Simple appendicitis was defined as any form of inflammation of the appendix mucosa without perforation. Perforated appendicitis was defined as rupture of the appendix wall seen by the surgeon intra-operatively, or on histological analysis. WBC above 11, 000 mm3 or CRP above 10 mg/l was classified as raised.
Categorical variables of high/normal bilirubin and perforated/normal appendicitis were analysed with Fisher's exact test, a p value <0.05 will be significant. Statistical analysis was carried out using GraphPad Instat 3.10.
4. Results
From the 1st of January 2012 until 18th July 2012, 260 patients were admitted with RIF pain (see Fig. 1). Patients ranged from 5 to 85 years old, with a mean age of 27.8 years, 39% of whom were male. Patients with appendicitis had a mean age of 29.4 years, 55% of whom were male. 18 patients did not have LFTs requested and were excluded.
Fig. 1. Flowchart of patients admitted with right iliac fossa pain.
99 patients were diagnosed with conditions other than appendicitis (ovarian pathology, gastroenteritis, abdominal pain of unknown cause) and were managed non-operatively. 143 patients with suspected appendicitis underwent surgery; 2 of these patients were found at operation to have other diagnoses (Crohn's disease of the caecum and terminal ileum, caecal diverticulitis). 141 patients had their appendix removed; in 31 cases, histology was normal (22%). Histology revealed simple appendicitis in 89 (63%) cases, and perforated appendicitis in 19 (14%) cases. The 89 cases of simple appendicitis included acute, gangrenous and resolving appendicitis.
Of the 99 patients managed non-operatively for other diagnoses, 4 patients (4%) had high bilirubin levels with otherwise normal LFTs (see Table 1). Their diagnoses included 1 case of diverticulitis, 2 cases of ovarian cysts, and 1 case of abdominal pain of unknown origin. 2 of the 33 (6%) patients with normal appendix histology or alternative diagnoses had high bilirubin. 16 of the 74 (22%) of patients with simple appendicitis had high bilirubin levels, as did 14/20 (70%) of patients with perforated appendicitis. No patients with elevated bilirubin had raised ALP, and less than 2% of patients had mildly elevated transaminases.
Table 1. Bilirubin levels for each study group.
| High bilirubin > 20 μmol/L | Low bilirubin < 20 μmol/L | |
|---|---|---|
| Not appendicitis, conservative Mx (N) n = 99 | 4 | 95 |
| Normal appendix histology/alternate diagnosis (1) n = 33 | 1 | 32 |
| Non-perforated appendicitis (2) n = 91 | 16 | 74 |
| Perforated appendicitis (3) n = 17 | 14 | 6 |
To look at the diagnostic value of bilirubin in appendicitis (all types), we compared patients with appendicitis (simple or perforated) to patients managed non-operatively, or with normal appendix histology. We found a specificity of 0.96 for hyperbilirubinaemia in appendicitis, with a positive predictive value of 0.86, and an odds ratio of 9.53 (see Table 2). Sensitivity (0.27) and negative predictive value (0.61) were lower. The specificity was higher than WBC (0.71) and CRP (0.612). Fisher's exact test showed a statistically significant association for bilirubin, WBC and CRP with appendicitis vs RIF pain of other origin.
Table 2. Bilirubin vs WBC vs CRP for appendicitis vs RIF pain.
| Appendicitis vs RIF pain of other origin | ||||||
|---|---|---|---|---|---|---|
| Bili | 2, 3a | 1, Nb | Specificity | 0.96 (0.92–0.98) | Odd's Ratio 9.53 (3.34–29.3) | |
| +ve | 30 | 5 | Sensitivity | 0.27 (0.22–0.30) | ||
| −ve | 80 | 127 | PPV | 0.86 (0.70–0.95) | Fisher's 2 sided p value < 0.0001 | |
| NPV | 0.61 (0.59–0.63) | |||||
| WBC | 2, 3 | 1, N | Specificity | 0.71 (0.65–0.76) | Odd's Ratio 5.11 (2.85–9.20) | |
| +ve | 75 | 39 | Sensitivity | 0.68 (0.61–0.75) | ||
| −ve | 35 | 93 | PPV | 0.66 (0.59–0.72) | Fisher's 2 sided p value < 0.0001 | |
| NPV | 0.73 (0.67–0.76) | |||||
| CRP | 2, 3 | 1, N | Specificity | 0.62 (0.56–0.66) | Odd's Ratio 7.29 (3.85–13.9) | |
| +ve | 90 | 50 | Sensitivity | 0.82 (0.75–0.88) | ||
| −ve | 20 | 81 | PPV | 0.64 (0.59–0.69) | Fisher's 2 sided p value < 0.0001 | |
| NPV | 0.80 (0.73–9.86) | |||||
- a
Appendicitis (simple and perforated).
- b
Not appendicitis (normal appendix histology, alternate diagnoses).
Hyperbilirubinaemia in perforated appendicitis vs simple appendicitis had a specificity of 0.82 for perforated appendicitis, a sensitivity of 0.70 and an odds ratio of 10.8 (see Table 3). Comparing bilirubin to WBC and CRP in perforated appendicitis, bilirubin had a higher specificity (0.82) than both WBC (0.34) and CRP (0.21), but a lower sensitivity (0.70 vs 0.80 and 0.95 respectively). Fisher's exact test showed a statistically significant p value for bilirubin, but not WBC or CRP, with perforated appendicitis.
Table 3. Bilirubin vs WBC cs CRP for perforated appendicitis vs simple appendicitis. +ve/−ve = high or low test scores (bilirubin > 20 μmol/L, WBC > 11 × 103/μL, CRP > 10 mg/L). 95% confidence intervals in brackets.
| Perforated vs simple appendicitis | ||||||
|---|---|---|---|---|---|---|
| Bili | 3a | 2b | Specificity | 0.82 (0.77–0.86) | Odd's Ratio 10.79 (3.22–37.8) | |
| +ve | 14 | 16 | Sensitivity | 0.70 (0.48–0.86) | ||
| −ve | 6 | 74 | PPV | 0.47 (0.32–0.58) | Fisher's 2 sided p value < 0.0001 | |
| NPV | 0.93 (0.87–0.96) | |||||
| WBC | 3 | 2 | Specificity | 0.34 (0.30–0.37) | Odd's Ratio 2.10 (0.59–8.19) | |
| +ve | 16 | 59 | Sensitivity | 0.80 (0.58–0.93) | ||
| −ve | 4 | 31 | PPV | 0.21 (0.16–0.25) | Fisher's 2 sided p value = 0.29 | |
| NPV | 0.89 (0.76–0.96) | |||||
| CRP | 3 | 2 | Specificity | 0.21 (0.17–0.22) | Odds Ratio 5.09 (0.654–108.29) | |
| +ve | 19 | 71 | Sensitivity | 0.95 (0.76–1.00) | ||
| −ve | 1 | 19 | PPV | 0.21 (0.17–0.22) | Fisher's 2 sided p value = 0.116 | |
| NPV | 0.95 (0.76–1.00) | |||||
- a
Perforated appendicitis.
- b
Simple appendicitis.
Table 4. Biochemical values for each study group. p values calculated using Kruskal–Wallis test. Mean = average, sd = standard deviation, +ve = positive test (bilirubin > 20 μmol/L, WBC > 11 × 103/μL, CRP > 10 mg/L).
| 1 | 2 | 3 | N | p Value | ||
|---|---|---|---|---|---|---|
| Bili | Mean | 7.32 | 14.69 | 25.88 | 9.71 | p < 0.0001 |
| sd | 3.28 | 9.64 | 19.61 | 6.65 | ||
| +ve | 0 | 17 | 12 | 4 | ||
| −ve | 31 | 74 | 5 | 89 | ||
| WBC | Mean | 10.62 | 13.08 | 14.97 | 8.99 | p < 0.0001 |
| sd | 5.43 | 4.74 | 6.2 | 3.23 | ||
| +ve | 11 | 59 | 13 | 24 | ||
| −ve | 20 | 32 | 4 | 69 | ||
| CRP | Mean | 23.62 | 63.33 | 131.64 | 29.3 | p < 0.0001 |
| sd | 49.18 | 81.71 | 101.98 | 56.78 | ||
| +ve | 9 | 72 | 16 | 38 | ||
| −ve | 21 | 19 | 1 | 55 | ||
We also looked at the mean values for bilirubin, WBC and CRP within our different categories. We found that all values increased with progression of appendicitis severity, which was statistically significant (p < 0.0001) when using the Kruskal–Wallis test for non-parametric data (Table 4).
5. Discussion
Bilirubin is not commonly known to be a relevant marker in appendicitis. However, previous studies have found hyperbilirubinaemia to be a marker with high specificity for perforated appendicitis. Adult bilirubin levels in the adult surgical population are usually raised due to liver or gallbladder problems. Gilbert's syndrome may cause an idiopathic, isolated unconjugated hyperbilirubinaemia. However, the prevalence of Gilbert's syndrome is expected to be around 6%,10 which is considerably less than the prevalence we found in simple appendicitis (18.7%) and perforated appendicitis (70.6%).
Hepatic dysfunction as a result of bacterial infection or sepsis without direct invasion of the liver, has already been well described.11, 12 The possible aetiologies include gram negative sepsis, shock and ischaemic liver, severe trauma or gut barrier failure.13 Gram negative organisms, with Escherichia coli in particular, have been shown to produce endotoxins that affect bile flow in rat liver models.14, 15 None of the patients in our study had ischaemic liver, or septic shock.
In appendicitis, compromised appendix wall integrity leads to translocation of bacteria and endotoxins from the appendix lumen into the portal system. Inflammatory cytokines may then travel to the liver, inducing intrahepatic cholestasis. Research has also shown that E. coli endotoxin causes dose dependent cholestasis,16 which would explain our findings of increased bilirubin levels with progressive appendicitis severity. It is possible that bilirubin may be raised in other sources of gram-negative related sepsis, which may be of a gastrointestinal origin (E. coli in diverticulitis) or from other sources such as pneumonia, endocarditis, pyelonephritis and soft-tissue abscesses.17
The prospective nature of our study, with inclusion of all patients with RIF pain, revealed an original finding—that hyperbilirubinaemia predicts appendicitis (simple and perforated) in patients admitted with RIF pain. Given the large volume of patients with RIF pain seen by an emergency general surgical team, we felt it was important to include this non-operative group in our study design. The specificity of hyperbilirubinaemia of 0.96 for appendicitis is very high, and should alert the clinician to the possibility of this diagnosis.
Our secondary outcome confirmed that there is a high specificity of bilirubin (0.82) for perforated appendicitis, matching results from the literature3, 4, 5, 6, 7, 8, 9 (see Table 5). Our odds ratio of 10.8 is higher than has so far been reported in most papers (range 2.96–9.85). WBC and more recently CRP are useful laboratory blood tests,18, 19, 20, 21 and indeed have a much higher sensitivity than bilirubin for appendicitis, but a lower specificity. This confirms the use of hyperbilirubinaemia as a rule-in, not rule-out test for appendicitis.
Table 5. Summary of previous studies.
| Study | Type of study | Sample size | Findings |
|---|---|---|---|
| Estrada et al., 20074 | Retrospective | 170 | Hyperbilirubinaemia (17.1 μmol/L) and perforated appendicitis
|
| Sand et al., 20093 | Retrospective | 538 | Hyperbilirubinaemia (26.5 μmol/L) and perforated appendicitis
|
| Kaser et al., 20105 | Retrospective | 725 | Hyperbilirubinaemia (20 μmol/L) and perforated appendicitis
|
| Atahan et al., 20117 | Retrospective | 351 | Hyperbilirubinaemia (17.1 μmol/L) and perforated appendicitis
|
| Emmanuel et al., 20116 | Retrospective | 472 | Hyperbilirubinaemia (20.5 μmol/L) and simple appendicitis
|
| Khan, 20089 | Prospective | 110 | Hyperbilirubinaemia (18.81 μmol/L) and perforated appendicitis
|
| Beltran et al., 20098 | Prospective | 134 | Hyperbilirubinaemia (17.86 μmol/L) and perforated appendicitis
|
The diagnosis of appendicitis is still based on a patient's clinical presentation, and the judgement of the emergency surgeon. The most common investigative adjuncts are blood tests (WBC and more recently, CRP), urinalysis and imaging. CT has a very high diagnostic accuracy (93–98%22) but is used less often in Europe.23 This is due to concerns over irradiation of the predominantly young patient population with appendicitis. Cost also may be a factor. While CT has high diagnostic accuracy for appendicitis, this study has confirmed that hyperbilirubinaemia can predict perforation with high specificity. In Europe, diagnostic laparoscopy now plays an increasingly important role in the evaluation of RIF pain. As appendicectomy is carried out routinely during these operations, there has been a concurrent increase in the negative appendicectomy rate in some trusts.24, 25 A correct pre-operative diagnosis could reduce the number of possibly unnecessary operations with the costs of theatre time, hospital stay and time off work to recover, as well as the risks of complications.
Methodological limitations to this study included the possibility of discharged patients presenting with appendicitis at other hospitals. A multivariate statistical analysis was beyond the resources of this study. Our recruited numbers were limited by the duration of the investigator's surgical rotation; an adequately powered study would require a sample size of 418 patients.
6. Conclusion
Our findings confirm that hyperbilirubinaemia has a high specificity for distinguishing acute appendicitis, especially when perforated, from other causes of RIF pain, particularly those not requiring surgery.
Ethical approval
Not required.
Funding
None.
Author contribution
Nigel D'Souza: study design, data collection, data analysis, writing.
Diallah Karim: data collection.
Rame Sunthareswaran: data analysis.
Conflict of interest
None.