E. Laboratory evaluation of Acute Abdominal Pain
A complete blood count with cell count differential is important in the assessment of surgical conditions and should be obtained in every patient with acute abdominal pain.
White blood cell (WBC) count elevation may indicate the presence of an infectious source.
Left shift on the differential to more immature forms is often helpful because this may indicate the presence of an inflammatory source even if the WBC count is normal.
Hematocrit elevation may be due to volume contraction from dehydration. Conversely, a low hematocrit may be due to occult blood loss.
An electrolyte profile may reveal clues to the patient’s overall condition.
Hypokalemic, hypochloremic, metabolic alkalosis may be seen in patients with prolonged vomiting and severe volume depletion. The hypokalemia reflects the potassium–hydrogen ion exchange occurring at the cellular level in an effort to correct the alkalosis.
Elevation of the blood urea nitrogen or creatinine is also indicative of volume depletion.
Liver enzyme levels may be obtained in the appropriate clinical setting.
A mild elevation of transaminases (<2 times normal), alkaline phosphatase, and total bilirubin is sometimes seen in patients with acute cholecystitis.
A moderate elevation of transaminases (>3 times normal) in the patient with acute onset of RUQ pain is most likely due to a common bile duct (CBD) stone. Elevation of the transaminases often precedes the rise in total bilirubin and alkaline phosphatase in patients with acute biliary obstruction.
Markedly elevated transaminases (i.e., >1,000 IU/L) in the patient without pain are more likely due to hepatitis or ischemia.
Pancreatic enzymes (amylase and lipase) should be measured if the diagnosis of pancreatitis is considered. It is important to note that the degree of enzyme elevation does not correlate with the severity of the pancreatitis.
Mild degrees of hyperamylasemia may be seen in several situations, such as intestinal obstruction.
Elevation of lipase usually indicates pancreatic parenchymal damage.
Lactic acid level may be obtained when considering intestinal ischemia.
Serum lactate is an indicator of tissue hypoxia.
Mild lactic acidosis may be seen in patients with arterial hypotension.
Ongoing elevation of serum lactate despite resuscitation is indicative of progression of tissue ischemia (e.g., mesenteric ischemia).
Urinalysis is helpful in assessing urologic causes of abdominal pain.
Bacteriuria, pyuria, and a positive leukocyte esterase usually suggest a urinary tract infection (UTI). Recurrent UTI in males is unusual and should always elicit an evaluation.
Hematuria is seen in nephrolithiasis and renal and urothelial cancer.
β-Human chorionic gonadotropin must be obtained in any woman of child-bearing age. A positive urine result should be quantitated by serum levels.
A low level (<4,000 mIU) is seen in ectopic pregnancy.
Levels above 4,000 mIU indicate intrauterine pregnancy (i.e., one that should be seen on ultrasonography).