Ketones in Hyperemesis Gravidarum: Implications for Dehydration Status
Ketonuria is NOT a reliable indicator of dehydration status in hyperemesis gravidarum and should not be used to assess severity of dehydration. 1
Understanding Ketone Production in Hyperemesis
Ketones reflect starvation metabolism, not dehydration. When a pregnant patient with hyperemesis cannot maintain adequate oral intake, the body shifts to fat metabolism for energy, producing ketone bodies (primarily β-hydroxybutyrate) regardless of hydration status. 2, 3 This metabolic state occurs because:
- Adults require 150-200 grams of carbohydrate daily to prevent starvation ketosis, and this requirement persists even during acute illness. 2
- Without adequate carbohydrate intake, the liver continues producing ketones even if the patient is adequately hydrated. 2
- The presence of ketones indicates inadequate caloric/carbohydrate intake rather than volume depletion. 1
Proper Assessment of Dehydration in Hyperemesis
Focus on clinical signs and laboratory markers that actually reflect volume status:
Clinical Assessment
- Orthostatic hypotension (drop in blood pressure upon standing) 4
- Decreased skin turgor (skin tenting when pinched) 4
- Dry mucous membranes 4
- Tachycardia and hypotension from volume depletion 5
Laboratory Assessment
- Electrolyte abnormalities (elevated BUN/creatinine ratio, hypernatremia) 4
- Hemoconcentration (elevated hematocrit) 4
- Urine output and specific gravity 4
Critical Clinical Pitfall
Do not withhold IV fluids or delay rehydration based on absence of ketones. Conversely, do not assume adequate hydration simply because ketones are absent. 1 A patient can be severely dehydrated without ketonuria if they have been consuming carbohydrate-containing fluids (even in small amounts), or they can have significant ketonuria while being adequately hydrated if they simply haven't eaten. 2
Management Implications
When ketones are present in hyperemesis, this indicates:
- The patient requires both rehydration (if clinically dehydrated) and carbohydrate/caloric replacement. 2
- Normal saline (0.9% NaCl) with additional potassium chloride should be used for IV hydration, guided by daily electrolyte monitoring. 1
- Once the patient can tolerate oral intake, provide carbohydrate-containing fluids to suppress ketone production. 2
- Thiamine supplementation (100 mg three times daily orally or IV as part of vitamin B complex) should be given to all women admitted with vomiting or severely reduced dietary intake, especially before administering dextrose. 1
Special Consideration in Diabetic Pregnancy
In pregnant patients with diabetes, ketones have different implications. Pregnant individuals may present with euglycemic diabetic ketoacidosis (glucose <200 mg/dL), and the diagnosis may be complicated by mixed acid-base disturbances in the setting of hyperemesis. 4 In this specific population, ketones combined with metabolic acidosis (pH <7.3, bicarbonate <15 mEq/L) indicate diabetic ketoacidosis requiring immediate medical attention, not simply starvation ketosis. 2, 3
For non-diabetic hyperemesis patients, measure β-hydroxybutyrate if available rather than urine ketones, as direct blood measurement is more accurate. 2, 5 However, remember that the presence or absence of ketones does not determine hydration status or treatment urgency—clinical assessment does. 1