Nausea & Vomiting: Common Causes and When It's Serious

Common Causes

References

Sources cited on this page. PubMed links open the original abstract.

1. Quigley EM, Hasler WL, Parkman HP. AGA technical review on nausea and vomiting. Gastroenterology. 2001;120(1):263–286. PMID 11208736 · doi:10.1053/gast.2001.20516

When Nausea and Vomiting Warrant Blood Tests

Acute nausea and vomiting lasting fewer than 24 hours is most often self-limiting – typically viral gastroenteritis or dietary indiscretion – and requires no blood investigation in an otherwise healthy adult. Blood tests become essential when vomiting is severe, prolonged (beyond 48 hours), accompanied by systemic features (fever, severe pain, jaundice, confusion), occurs in a known diabetic, or presents in pregnancy, where hyperemesis gravidarum can cause serious metabolic derangement.¹

The most important initial blood panel for persistent vomiting addresses three questions: Has significant metabolic disruption occurred (electrolytes, renal function)? Is there an underlying organ pathology driving the nausea (liver function, amylase for pancreatitis, glucose for diabetic ketoacidosis)? And – in anyone of reproductive age – is this pregnancy-related (beta-hCG)? These tests are complementary and are typically run simultaneously from a single blood draw in an emergency or urgent care setting.

Metabolic Derangements Caused by Prolonged Vomiting

Prolonged vomiting causes a characteristic pattern of electrolyte and acid-base disturbances. Loss of gastric acid (hydrochloric acid) depletes hydrogen ions, producing metabolic alkalosis. Simultaneously, renal compensation retains bicarbonate and excretes potassium, causing hypokalaemia – which, in turn, worsens the alkalosis. The biochemical pattern in significant vomiting is therefore: low chloride, low potassium, elevated bicarbonate, and elevated pH. Creatinine and urea rise as dehydration reduces glomerular filtration (pre-renal uraemia); the urea:creatinine ratio typically exceeds 100:1 (in SI units) in dehydration from vomiting, a useful pointer when the history is unclear.²

In hyperemesis gravidarum – severe nausea and vomiting of pregnancy requiring hospital admission – electrolyte replacement guided by blood results is the mainstay of treatment. Thiamine (vitamin B1) deficiency is a serious risk in hyperemesis; Wernicke's encephalopathy has occurred in undertreated cases. Thiamine should be supplemented empirically before dextrose infusion in any patient with prolonged vomiting, as glucose administration in a thiamine-depleted state can precipitate acute neurological deterioration.

Organ-Specific Causes Identified by Blood Tests

Acute pancreatitis presents with epigastric pain and vomiting; serum amylase and lipase are elevated – typically to three times the upper limit of normal – within hours of onset, with lipase remaining elevated longer and being more specific.³ Liver function tests distinguish hepatitis (markedly elevated transaminases with nausea and vomiting) from biliary obstruction (raised bilirubin and alkaline phosphatase, with jaundice). In diabetic ketoacidosis, nausea and vomiting are cardinal features – glucose is markedly elevated, bicarbonate is low (metabolic acidosis), and ketones are detectable in blood and urine; this is a medical emergency requiring urgent fluid and insulin therapy. Addisonian crisis (acute adrenal insufficiency) can present with nausea, vomiting, and hypotension; a random cortisol below 400 nmol/L in a severely unwell patient strongly supports the diagnosis and warrants immediate hydrocortisone treatment.

How long it has lasted changes what matters

Duration is the single most useful piece of information. Nausea and vomiting lasting under 48 hours is usually infective or dietary and needs attention to fluids rather than investigation. Beyond about a week, the likely causes shift towards medication effects, pregnancy, gastro-oesophageal reflux, gallbladder disease, gastroparesis in long-standing diabetes, and less commonly raised pressure inside the skull. Vomiting that has come and gone for months, particularly if it relates to meals, points elsewhere again, towards obstruction, ulcer disease or a motility problem.

Features that change the urgency

• Blood in the vomit, whether fresh red or dark like coffee grounds, needs urgent assessment.
• Vomiting with severe abdominal pain, especially if the abdomen is rigid or tender to release, or if you cannot pass wind or stool.
• Vomiting with a severe headache, neck stiffness or new confusion, or vomiting that is worse on waking and unaccompanied by nausea.
• Signs of significant dehydration: passing very little urine, dizziness on standing, a dry mouth with sunken eyes, or lethargy.
• Inability to keep any fluid down for more than 24 hours, which matters sooner in young children, older adults and people with diabetes.

Rehydration that actually works

The instinct to drink a large glass of water usually triggers another episode. Small volumes taken often are tolerated far better: a few sips every ten to fifteen minutes, increasing gradually once they stay down. Plain water alone is not ideal after repeated vomiting because it replaces neither salt nor glucose; oral rehydration salts, which contain both in the proportions that drive absorption, are more effective and are inexpensive. Fizzy drinks and undiluted fruit juice are poor choices, as their sugar concentration can worsen diarrhoea if that is present too.

Medicines and blood sugar during illness

Vomiting complicates several long-term medications. People with diabetes should not simply stop insulin when unable to eat, as the risk of ketoacidosis rises; the usual advice is to keep testing and seek guidance rather than omit doses. Diuretics, ACE inhibitors, ARBs and metformin are often paused temporarily during significant vomiting or diarrhoea because of the strain on the kidneys, but that decision belongs to your prescriber. If you take steroids long term, vomiting is a specific reason to seek advice quickly, because doses may need to be increased rather than skipped.