Wednesday, May 26

Urinalysis

One study of 500 patients with acute appendicitis revealed that approximately one third reported urinary symptoms, most commonly dysuria or right flank pain. One in 7 patients had pyuria greater than 10 WBC per high power field, and 1 in 6 patients had greater than 3 RBC per high power field. Thus, the diagnosis of appendicitis should not be dismissed due to the presence of urologic symptoms or abnormal urinalysis.

C-reactive protein test

C-reactive protein (CRP) is an acute-phase reactant synthesized by the liver in response to infection or inflammation. A rapid assay is widely available.
Several prospective studies (Thimsen 1989, Albu 1994, de Carvalho 2003) have shown that, in adults who have had symptoms for longer than 24 hours, a normal CRP level has a negative predictive value of 97-100% for appendicitis.
In a 1989 study of 70 patients, Thimsen et al noted that a normal CRP level after 12 hours of symptoms was 100% predictive of benign, self-limited illness.7
Multiple studies have examined the sensitivity of CRP alone for the diagnosis of appendicitis in patients selected to undergo appendectomy.
  • Gurleyik et al, in 1995, found that 87 of 90 patients with histologically proven appendicitis had an elevated CRP, a sensitivity of 96.6%.
  • Shakhetrah, in 2000, found that 85 of 89 patients with histologically proven appendicitis had an elevated CRP, a sensitivity of 95.5%.
  • Asfar et al, in 2000, completed a prospective double blind study of 78 patients undergoing appendectomy and found that CRP had a sensitivity of 93.6%.
  • Erkasap et al, in 2000, prospectively studied the more relevant group of 102 adult patients with RLQ pain, 55 of whom proceeded to appendectomy. In this group, the sensitivity of CRP was 96%.
Investigators have also studied the ability of combinations of WBC and CRP to reliably rule out the diagnosis of appendicitis.
  • Gronroos, in 1999, studied 300 patients operated for suspected appendicitis (200 positive, 100 negative) and found that WBC or CRP was abnormal in all 200 patients with appendicitis.
  • Ortega-Deballon et al, in 2008, prospectively studied patients referred to a surgeon for RLQ pain and found that normal WBC and CRP had a negative predictive value of 92.3% for the presence of appendicitis.
  • Yang, in 2006, retrospectively studied 897 patients who underwent appendectomy (740 with appendicitis, 157 without) and found that only 6 of 740 patients with appendicitis had WBC <10,500 cells/mm3 AND neutrophilia <75%, AND a normal CRP. This yields a sensitivity of 99.2% for the "triple screen".
Some studies have examined the sensitivity of combined WBC and CRP in the subpopulation of patients older than 60 years.
  • Gronroos, in 1999, studied 83 patients older than 60 years who underwent appendectomy (73 found to have appendicitis) and found that no patient with appendicitis had both normal WBC and CRP.
  • Yang et al, in 2005, retrospectively studied 77 patients older than 60 years with histologically proven appendicitis and found that only 2 had a normal "triple screen."
Several studies have examined the accuracy of CRP and WBC in the subpopulation of pediatric patients with suspected appendicitis.
  • Gronroos, in 2001, studied 100 children with pathology-proven appendicitis and found that both WBC and CRP were normal in 7 of the 100 patients.
  • Mohammed, in 2004, prospectively studied 216 children admitted for suspected appendicitis and found triple screen sensitivity and negative predictive value of 86% and 81%, respectively.
  • Stefanutti et al, in 2007, prospectively studied more than 100 children undergoing surgery for suspected appendicitis and found that either WBC or CRP was elevated in 98% of those with pathology-proven appendicitis (CI, 95.3-100%).
CRP is nonspecific and does not distinguish between various types of infection or inflammation.

Workup

Laboratory Studies

Complete blood cell count
Studies consistently show that 80-85% of adults with appendicitis have a WBC count greater than 10,500 cells/mm3. Neutrophilia greater than 75% occurs in 78% of patients. Fewer than 4% of patients with appendicitis have a WBC count less than 10,500 cells/mm3 and neutrophilia less than 75%.
Dueholm et al, in 1989, further delineated the relationship between WBC count and the likelihood of appendicitis by calculating likelihood ratios for defined intervals of the WBC count.