Appendicitis

It’s been a long night and you grab the last chart in the rack. You walk in the room and find a 20 your old laying on the gurney. On exam he is tender in the right lower quadrant so you give him a small amount of pain medicine and order your labs. An hour later you come back to re-examine him and he’s not as tender as before and wants to leave. His white count is normal and he’s never had a fever. You wonder, Do I really need to get the CT to rule out appendicitis or can I just let him go, finish my paper work, and sign out to replacement?

 

Reviewed by Brian Weisenberg, MD.
Column Organized by Evan Schwarz, MD
Washington University in St. Louis
Division of Emergency Medicine

 

Cardall T, Glasser J, Guss DA.  Clinical value of the total white blood cell count and temperature in the evaluation of patients with suspected appendicitis.  Academic Emergency Medicine.  October 2004; 11 (10):  1021-1027.

 This article is a prospective consecutive case series which evaluates the diagnostic value of the total white blood cell count (WBC) and body temperature in patients presenting to the emergency department with signs and symptoms of appendicitis.  The results of this study suggest that an elevated white count and temperature have little clinical utility in diagnosing or ruling out appendicitis in the emergency department
 Two hundred ninety three patients who presented with a history and physical exam suggestive of appendicitis were enrolled consecutively.  The population included males and females with a mean age of 30.8 years (range 7-75).  Age, gender, total WBC count, highest documented temperature in the emergency department, the results of CT scans, and operative reports were recorded.  WBC counts greater than 10,000 cells/mm3 and temperatures greater than 99 °F were considered abnormal.
 Ninety-two of the 293 (31%) patients were diagnosed with appendicitis.  Total white blood cell count was measured in 274 patients.  The specificity and sensitivity of leukocytosis for appendicitis was 52% and 76% (See Table 1).  The positive predictive value for an elevated WBC count was 42% and the negative predictive value was 82%.  In general, a high sensitivity test (i.e. greater than 90-95%) is helpful in ruling out a diagnosis in the presence of a negative result.  Thus, the sensitivity of 76% for leukocytosis  implies a 24% chance for a negative test result when the patient actually has appendicitis (false negative).   This assumes an unacceptably high risk when appendicitis is included in the differential diagnosis.  

 

Table 1. Total WBC Count and Appendicitis
Total WBC   (1,000 cells/mm3)	Not Appendicitis	Appendicitis	Totals
≤ 10,000	98 (52%)	21 (24%)	119
>  10,000	89 (48%)	66 (76%)	155
Totals	187 (100%)	87 (100%)	274

 

The positive likelihood ratio (+LR) for leukocytosis was 1.59 and the negative likelihood ratio (-LR) was 0.46.  The authors also calculated positive likelihood ratios for different WBC count intervals.  Counts greater than 12,000 cells/mm3 had the highest +LR’s at 2.70. Positive likelihood ratios greater than 10 are generally considered diagnostic given a positive test result and negative likelihood ratios less than 0.1 rule out a disease given a negative test result.   As such, these likelihood ratios suggest that the presence of leukocytosis dose little to change the post-test probability that a patient has appendicitis and therefore does not aid the clinician’s diagnosis. 
Elevated temperature (> 99.0 °F) was found to have a sensitivity of 47% and specificity of 64% with a NPV of 72% and a PPV of 37%.  The +LR was 1.3 and –LR was 0.82 (See Table 2).  Likelihood ratios for a range of temperatures were also calculated.  When analyzed in terms of specific temperature intervals, the highest likelihood ratio (3.18) was found in patients with temperatures greater than 102 °F.   As with leukocytosis, these results show the presence of fever has little diagnostic utility for acute appendicitis.

 

Table 2.  Temperature and appendicitis
Temperature °F	Not Appendicitis	Appendicitis	Totals
<99.0	129 (64%)	49 (53%)	178
>99.0	72 (36%)	43 (47%)	115
Totals	201	92	193

 

The positive likelihood ratio (+LR) for leukocytosis was 1.59 and the negative likelihood ratio (-LR) was 0.46.  The authors also calculated positive likelihood ratios for different WBC count intervals.  Counts greater than 12,000 cells/mm3 had the highest +LR’s at 2.70. Positive likelihood ratios greater than 10 are generally considered diagnostic given a positive test result and negative likelihood ratios less than 0.1 rule out a disease given a negative test result.   As such, these likelihood ratios suggest that the presence of leukocytosis dose little to change the post-test probability that a patient has appendicitis and therefore does not aid the clinician’s diagnosis. 

Elevated temperature (> 99.0 °F) was found to have a sensitivity of 47% and specificity of 64% with a NPV of 72% and a PPV of 37%.  The +LR was 1.3 and –LR was 0.82 (See Table 2).  Likelihood ratios for a range of temperatures were also calculated.  When analyzed in terms of specific temperature intervals, the highest likelihood ratio (3.18) was found in patients with temperatures greater than 102 °F.   As with leukocytosis, these results show the presence of fever has little diagnostic utility for acute appendicitis.