Abdominal Pain - Diagnostic Studies

Imaging

Plain abdominal radiography

When compared to unenhanced helical CT, 3-view xrays demonstrated:

• Sensitivity = 30%, Specificity = 88%, Accuracy = 56%
• Negative predictive value = 51%
• Pearl: A 3-way acute abdominal series is too insensitive to rule-out any major acute causes of abdominal pain with confidence. No need to order routinely. If you are worried about a perforated viscus, order an upright chest x-ray instead -- more accurate and less radiation.

Obtain plain film if suspicious for:

• Pneumoperitoneum (although upright CXR is better)
• Small bowel obstruction (where CT not readily available)
• Localization of foreign body ingestion or catheter

Abdominal/Pelvis CT

• Median radiation dose = 15-31 mSv (CXR has 0.1 mSv dose.)
• Oral contrast likely does NOT provide more information in acute abdominal pain. Known 241-minute delay.

Ultrasound

• Increasing use of bedside U/S for point of care testing in EDs.
• Advantage: can be used for unstable patients, no radiation exposure

Lactate

Lactate is useful adjunct to risk stratify for mortality (Shapiro et al. (2005))

Lactate	Level (mmol/L)	28-day in-hospital mortality	Early death (≤ 3d)
Low	<2.5	4.9%	1.5%
Medium	2.5-3.99	9.0%	4.5%
High	≥4	28.4%	22.4%

Diseases

Appendicitis: CT is first-line, unless pediatric or pregnant patient. Then U/S is first line. MRI is an alternative to avoid CT radiation risk.

Cholecystitis: Normal LFTs do NOT rule it out. LFT's helpful as adjunct to determine likelihood for common bile duct stone.

Diverticular disease: Prevalence <5% (age<40 yrs), 30% (age 41-60 yrs), 65% (age 61-85 yrs)

Ectopic pregnancy: Discriminatory zone for gestational sac is B-HCG ≥6,500 (transabdominal U/S) or B-HCG ≥1,500 (transvaginal U/S).

Mesenteric ischemia of concern because of subtleties in presentation.

• Multidetector CT angiography with reformats: sens 96%, spec 94%
• MR angiography: Sensitivity 85-90% (SMA), 75-90% (celiac artery), 25% (IMA)

Nephrolithiasis:

• Microscopic hematuria: sens 89%, spec 29%

Pancreatitis: Lipase (sens 90%, spec 93%) is better than amylase (sens 79%, spec 93%). Unlike level of elevated enzymes, CT correlates with severity.

UTI: Urine dipstick alone is adequately predictive, except for children, elderly, suspected urosepsis.

• Nitrites: Odds Ratio (OR) = 6.36
• Leukocyte esterase: OR = 4.52
• Blood: OR = 2.23

LUQ Pain: Limited use for labs/imaging, unless elderly, immunosuppressed, or trauma patient

References

• Shapiro NI, Howell MD, Talmor D, Nathanson LA, Lisbon A, Wolfe RE, Weiss JW.Serum lactate as a predictor of mortality in emergency department patients with infection. Ann Emerg Med. 2005 May;45(5):524-8. [PubMed]
• Panebianco NL, Jahnes K, Mills AM. Imaging and Laboratory Testing in Acute Abdominal Pain. Emerg Med Clin N Am. 2011;29:175-93. [PubMed]
• Ultrasonography vs. CT for suspected Nephrolithiasis. New England Journal of Medicine. 2014;371(26):2529-2531. [PubMed]