What is the role of lab testing in the diagnosis of homocystinuria?

Updated: Jul 27, 2018
  • Author: Pitchaiah Mandava, MD, PhD; Chief Editor: Helmi L Lutsep, MD  more...
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If patients present with systemic signs and symptoms, screening tests followed by confirmatory tests may be done.

The urine screening test for sulfur-containing amino acids, called the cyanide nitroprusside test, can be undertaken; however, high rates of false-negative as well as false-positive results are reported.

A neonatal screening test, called the Guthrie test, detects high levels of methionine in heel-stick blood. This test is performed routinely in several states for detection of phenylalanine, leucine, and methionine. Because of high false-negative results in homocystinuric patients, a recent report suggested lowering the threshold of methionine to qualify as abnormal.

Quantitative tests for homocystine in urine and blood are available commercially. The blood specimen needs to be handled in a specific manner described in the homocysteinemia testing section.

Measurement of CBS activity in cultured fibroblasts provides definitive support for the diagnosis.

Testing of amniotic cells and chorionic villi is also available.

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