Some causes of elevated chloride include dehydration, prolonged diarrhea, hypernatremia, renal tubular acidosis (hyperchloremic metabolic acidosis), metabolic acidosis , hyperparathyroidism, and drugs such as acetazolamide, methyldopa , cortisone ,estrogen, non-steroidal anti-inflammatory drugs (NSAIDs), and excessive bromide.

Some causes of decreased chloride levels include metabolic alkalosis, vomiting, diarrhea, congestive heart failure, syndrome of inappropriate secretion of ADH (SIADH), adrenal insufficiency (Addison's Disease), gastric suctioning, overhydration, salt-losing nephritis, burns, and some types of diuretic therapy.

References:

Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009 Dec;114(6):1326-31. PMID:19935037
Wallach, J. Interpretation of Diagnostic Tests, Eighth ed. Lippincott Williams & Wilkins, 2007 Fischbach FT, Dunning MB III, eds. A Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia, Lippincott Williams and Wilkins,2004