Is malabsorption (inability to absorb nutrients during digestion)
classified as a MEDICAL CONDITION or a SYMPTOM?  Are any of its causes
(lactose intolerance, short bowel syndrome, celiac disease, whipple's
disease) classified as "malabsorption syndromes" themselves -- or are
they just considered to include malabsorption as a symptom?

Most of the conditions you mentioned fall under section 9 of the ICD-9
codes -- diseases of the digestive system (520-579); however,
Whipple?s is classified under section 2 -- infectious and parasitic
diseases (001-139) while lactose intolerance is categorized under
section 3 -- endocrine, nutritional and metabolic diseases, and
immunity disorders (240-279).

Many other malabsorptive conditions fall under an umbrella "NOS" (not
otherwise specified) category of 579.9.  Here are a couple lists/codes
for you:

040.2 Whipple's disease 
Intestinal lipodystrophy 

271.3  Intestinal disaccharidase deficiciency and malabsorption
(lactose intolerance)

Malabsorption 579.9 

?	calcium 579.8 
?	carbohydrate 579.8 
?	disaccharide 271.3 
?	drug-induced 579.8 
?	due to bacterial overgrowth 579.8 
?	fat 579.8 
?	folate, congenital 281.2 
?	galactose 271.1 
?	glucose-galactose (congenital) 271.3 
?	intestinal 579.9 
?	isomaltose 271.3 
?	lactose (hereditary) 271.3 
?	methionine 270.4 
?	monosaccharide 271.8 
?	postgastrectomy 579.3 
?	postsurgical 579.3 
?	protein 579.8 
?	sucrose (-isomaltose) (congenital) 271.3 
?	syndrome 579.9 
?	postgastrectomy 579.3 
?	postsurgical 579.3 
http://www.dmi.columbia.edu/hripcsak/icd9

**************************

579  Intestinal malabsorption
579.0 Celiac disease
579.1 Topical sprue
579.2 Blind loop syndrome
579.3 Other and unspecified postsurgical nonabsorption
579.4 Pancreatic steatorrhea
579.8 Other specificed intestional malabsorption
579.9 Unspecified intestinal malabsorption

Hope this helps,
? V ?

Malabsorption is not a specific disease.  As you pointed out in your
question, it can occur in many different conditions, and is really a
symptom or manifestation of an underlying problem.

This article on eMedicine lays out some of the common symptoms and
causes of malabsorption.
http://www.emedicine.com/MED/topic1384.htm