Gastroenteritis: This is a common condition that can cause nausea, vomiting, diarrhea, and an increase in lactate levels due to dehydration and poor perfusion. The absence of acidosis might be due to early presentation or mild disease.

Food Poisoning: Similar to gastroenteritis, food poisoning can lead to the symptoms described and may cause an increase in lactate due to the body's response to the toxin.
Inflammatory Bowel Disease (IBD) Flare: Conditions like Crohn's disease or ulcerative colitis can cause severe gastrointestinal symptoms and may lead to increased lactate levels due to inflammation and potential sepsis.
Medication-Induced Gastrointestinal Disturbance: Certain medications can cause nausea, vomiting, and diarrhea as side effects, potentially leading to increased lactate levels.

Septic Shock: Although the patient does not have acidosis, early septic shock can present with nonspecific symptoms like nausea, vomiting, and diarrhea. The increase in lactate is a key indicator of tissue hypoperfusion.
Mesenteric Ischemia: This is a life-threatening condition that can cause abdominal pain, nausea, vomiting, and diarrhea. The absence of acidosis does not rule out this diagnosis, as it can develop later.
Toxic Ingestion: Certain toxic ingestions can cause gastrointestinal symptoms and increased lactate without initial acidosis.

Mitochondrial Disorders: These are a group of disorders that affect the mitochondria, leading to impaired energy production. They can cause a variety of symptoms, including gastrointestinal issues and elevated lactate levels.
D-Lactic Acidosis: This is a rare condition that occurs when the body produces D-lactate, which is not typically measured in standard lactate tests. It can cause neurological symptoms and gastrointestinal issues.
Short Bowel Syndrome: This condition, resulting from a significant loss of intestinal tissue, can lead to malabsorption, diarrhea, and potentially increased lactate levels due to bacterial overgrowth or other complications.