Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (653 page)

   Twenty-four–hour collections are generally recommended, but random collections may be used. Refrigeration is the most important aspect of specimen preservation.

   Urinary 5-HIAA is increased with malabsorption, in 75% of cases, usually when a carcinoid tumor is far advanced (with large liver metastases, often 300–1,000 mg/day), but may not be increased despite massive metastases.

   Sensitivity is 73%.

   The test is useful in the diagnosis of only 5–7% of patients with carcinoid tumors but in approximately 45% of those with liver metastases.

   Disease extent and prognosis correlate generally with urine 5-HIAA excretion, and the level becomes normal after successful surgery. If urine HIAA is normal, the blood level of serotonin or a precursor, 5-hydroxytryptophan should be checked.

5
′
-NUCLEOTIDASE (5¢-RIBONUCLEOTIDEPHOSPHOHYDROLASE, 5
′
-NT)

   Definition

   This membrane-bound enzyme of the liver is increased in diseases of the liver, particularly if the hepatobiliary tract is involved. The appearance of 5′-NT in serum is due to cholestasis, and its significance is similar to that of ALP and GGT. However, 5′-NT is not as subject to drug induction as GGT and ALP, and it is not subject to confusion with alternate sources of the enzyme, as is seen with ALP.

   
Normal range:
2.0–8.0 U/L.

   Use

   Determining cholestatic liver disease, particularly when GGT and ALP could be falsely elevated due to drug induction

   Better test for secondary tumors and lymphomas of the liver than ALP

   Interpretation

Increased In

   5′-NT is increased in the following conditions: