These consensus criteria summarized below were published in the American Journal of Medical Genetics in 2000. Making a clinical diagnosis of HHT in individuals displaying the classical triad of nosebleeds, telangiectasia, and a suitable family history is relatively simple, but this accounts for only a proportion of cases. Often subtle disease manifestations are overlooked in HHT families, particularly involvement of internal organs.

CLINICAL DIAGNOSTIC CRITERIA FOR HHT

1. 1. NOSEBLEEDS, spontaneous and recurrent.
2. 2. TELANGIECTASES, multiple, at characteristic sites including lips, oral cavity, fingers and nose.
3. 3. INTERNAL LESIONS such as
   1. Gastrointestinal telangiectasia (with or without bleeding)
   2. Pulmonary AVM
   3. Hepatic AVM
   4. Cerebral AVM
   5. Spinal AVM
4. 4. FAMILY HISTORY- a first degree relative with HHT according to these criteria.

The HHT Diagnosis is:

- Definite if 3 criteria are present
- Possible or suspected if 2 criteria are present
- Unlikely if fewer than 2 criteria are present.

Several features of these diagnostic criteria should be noted. First, they spell out in detail exactly what is required for each manifestation of HHT. For example, as there is no agreement amongst doctors as to the precise number of episodes or severity of nosebleeds needed to satisfy a diagnosis of HHT, the criteria merely highlight that nosebleeds should occur spontaneously on more than one occasion, with night-time bleeds being particularly suspicious. Secondly, they emphasize the importance of taking a detailed, targeted, family history in order to establish the diagnosis of this highly penetrant, but extremely variable, dominant genetic disorder in an individual. Also, these criteria allow us to distinguish between individuals who definitely have HHT, and those in whom it is suspected, and allow each label to be added to medical records to ensure appropriate follow-up and medical management. Finally, we emphasize that all offspring of an individual with HHT are at risk of having the disease since HHT may not manifest until late in life. We recommend that if there is any concern regarding the presence or absence of physical signs, a physician experienced with HHT should be consulted.

REFERENCES
Plauchu H, de Chadar�vian J-P, Bideau A and Robert J-M. Age-related profile of hereditary hemorrhagic telangiectasia in an epidemiologically recruited population. American Journal of Medical Genetics, 1989 32:291-7.
Shovlin CL , Guttmacher AE , Buscarini E, Faughnan ME, Hyland RH, Westermann CJJ, Kjeldsen AD, and Plauchu H. . Diagnostic Criteria For Hereditary Hemorrhagic Telangiectasia (Rendu-Osler-Weber Syndrome). American Journal of Medical Genetics. 2000 Mar 6:91 (1): 66-7.