E70.5

Billable

Disorders of tryptophan metabolism

HCC Category Mapping

V24HCC 23 — Other Significant Endocrine and Metabolic Disorders

0.230

ESRDHCC 23 — Other Significant Endocrine and Metabolic Disorders

0.000

RxHCCHCC 43 — Other Significant Endocrine and Metabolic Disorders

0.000

What This Code Means

Metabolic disorders affecting tryptophan (an essential amino acid) processing, which can impact serotonin and niacin production.

Coding Tips

•This code encompasses various tryptophan metabolism disorders; review documentation for specific conditions like Hartnup disease if applicable
•Consider associated conditions such as pellagra or neuropsychiatric symptoms that may result from tryptophan metabolism defects

Clinical Significance

Disorders of tryptophan metabolism encompass conditions affecting the processing of this essential amino acid, which is a precursor to serotonin and niacin. Hartnup disease is the most well-known condition in this category, presenting with pellagra-like skin rashes, cerebellar ataxia, and psychiatric symptoms due to impaired intestinal and renal tryptophan transport. Other tryptophan metabolism defects can cause similar neurological and dermatological manifestations.

Documentation Requirements

✓Documentation should specify the type of tryptophan metabolism disorder if possible, including Hartnup disease or other specific defects.
✓Supporting evidence includes urine amino acid analysis showing tryptophanuria, serum tryptophan levels, and any clinical manifestations (skin rash, ataxia, psychiatric symptoms).
✓Treatment with niacin supplementation and high-protein diet should be documented.
✓Genetic testing results should be included when available.

Commonly Confused Codes

E52 (Niacin deficiency/pellagra) may present similarly to Hartnup disease but has a dietary rather than metabolic etiology.E70.81 (Aromatic L-amino acid decarboxylase deficiency) affects tryptophan conversion to serotonin.E70.89 (Other disorders of aromatic amino-acid metabolism) is a broader category.L56.x (Drug phototoxicity) may mimic the skin findings.G11.x (Hereditary ataxia) may be confused clinically.

Code Hierarchy

└E70Disorders of aromatic amino-acid metabolism └E70.5Disorders of tryptophan metabolism

└E70.5Disorders of tryptophan metabolism