Gastrointestinal Loss: Conditions leading to chronic gastrointestinal loss, such as gastrointestinal bleeding or significant diarrhea, can result in a low anion gap metabolic acidosis due to the loss of bicarbonate-rich fluids. Elevated IgA can be seen in conditions like celiac disease, which also involves the gastrointestinal tract.

Nephropathic Cystinosis: This condition can lead to renal tubular acidosis (RTA), specifically type 1 (distal RTA), which is characterized by a normal anion gap metabolic acidosis. Elevated IgA levels can be associated with various renal diseases.
Chronic Diarrheal Conditions: Conditions such as inflammatory bowel disease (IBD) can cause both a low anion gap metabolic acidosis due to bicarbonate loss and elevated IgA levels, as IBD can stimulate IgA production.

Multiple Myeloma: Although less common, multiple myeloma can cause an elevation in IgA (as one of the types of monoclonal gammopathies) and renal impairment leading to acidosis. The anion gap might not always be elevated in cases of myeloma kidney, making it a "do not miss" diagnosis.
Amyloidosis: This condition can involve the kidneys and gastrointestinal tract, potentially leading to both a low anion gap metabolic acidosis and elevated IgA levels. Amyloidosis is a serious condition that requires early diagnosis.

Selective IgA Deficiency with Compensatory Increase in Other IgA-producing Conditions: This is a rare condition where there's a deficiency in IgA, but in some cases, other conditions might compensate by increasing IgA production in specific contexts, potentially leading to elevated serum IgA levels. The metabolic acidosis could be unrelated or due to a separate gastrointestinal issue.
Monoclonal Gammopathy of Undetermined Significance (MGUS) with IgA Elevation: MGUS can sometimes present with elevated IgA levels without significant symptoms. If associated with renal impairment, it could potentially lead to a low anion gap metabolic acidosis.