Differentials
Common
Vomiting
History
abdominal pain, may be a history of binge eating and vomiting consistent with a diagnosis of bulimia
Exam
may reveal abdominal distension and tenderness
1st investigation
- basic metabolic panel:
hypokalemia
- urine electrolytes and creatinine:
urine chloride is low (<15 mEq/L); urine potassium may be elevated
More - urine analysis and pH:
pH >7.0 if there is significant bicarbonaturia
- ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
Severe diarrhea
History
loose stools, may be colicky abdominal pain, dizziness
Exam
abdominal distension and tenderness, dry mucous membranes, lethargy, may be decreased skin turgor
1st investigation
- basic metabolic panel:
hypokalemia
- urine electrolytes and creatinine:
urine potassium <20 mEq/L
More - ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
Laxative and bowel cleansing agent use
History
history of laxative use (especially with chronic use or misuse), loose stools
Exam
abdominal distension and tenderness
1st investigation
- basic metabolic panel:
hypokalemia
More - urine electrolytes and creatinine:
urine potassium <20 mEq/L
More - ECG:
normal or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
Bulimia nervosa
History
recurrent episodes of binge eating and vomiting, frequently: low self-esteem; lack of confidence; and depressive thoughts
Exam
usually have normal physical appearance, may have dental enamel erosion, parotid gland enlargement, lanugo-like hair, and calluses on the dorsal surface of the hand
1st investigation
- basic metabolic panel:
hypokalemia
- urine electrolytes and creatinine:
urine chloride is low (<15 mEq/L); urine potassium may be elevated
More - urine analysis and pH:
pH >7.0 if there is significant bicarbonaturia
- ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
Anorexia nervosa
History
fatigue, dizziness, weight loss, amenorrhea, history of dieting, may exercise excessively, may be a history of binging and purging
Exam
low BMI, baggy clothing, low fat distribution with protruding bony structures (e.g., scapulae), orthostatic hypotension, bradycardia, if there is binging and purging there may be dental enamel erosion, scars on the dorsum of the hands and swollen salivary glands
1st investigation
- basic metabolic panel:
hypokalemia
- urine electrolytes and creatinine:
urine chloride may be low (<15 mEq/L); urine potassium may be elevated
More - urine analysis and pH:
pH >7.0 if there is significant bicarbonaturia
- ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
Drug-induced
History
history of use of diuretics, corticosteroids, beta-2 agonists (such as albuterol or terbutaline to prevent premature labor or to treat asthma), amphotericin B, history of chloroquine or theophylline toxicity; administration of vitamin B12 or folic acid in megaloblastic anemia or of granulocyte-macrophage colony-stimulating factor (GM-CSF) in neutropenia
Exam
normal or may have features of underlying disease; orthostasis or tachycardia may be present
1st investigation
- basic metabolic panel:
hypokalemia
- urine electrolytes and creatinine:
urine potassium levels >30 mEq/day and urine chloride levels >20 mEq/L with diuretic use
More - ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
Alcoholism
History
history of chronic alcohol intake
Exam
ascites, digital clubbing, disheveled appearance, gynecomastia, jaundice, malnutrition, palmar erythema, peripheral neuropathy, splenomegaly
1st investigation
- basic metabolic panel:
hypokalemia
More - ECG:
normal, or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
Diabetic ketoacidosis
History
history of diabetes, intercurrent illness, nonadherence with insulin therapy, polyuria, fatigue, weight loss, nocturia, rapid deterioration in clinical state with nausea, abdominal pain, vomiting
Exam
fever, tachycardia, dry mucous membranes, poor skin turgor, hypotension, and, in severe cases, shock
1st investigation
- basic metabolic panel:
hypokalemia, hyperglycemia
More - serum ketones:
elevated
- anion gap:
elevated
- ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
- ABG:
metabolic acidosis
Hyperosmolar hyperglycemic state
History
history of diabetes mellitus, polyuria, polydipsia, weight loss, lethargy, insidious onset of deterioration in clinical state, visual changes, drowsiness, lethargy
Exam
delirium, focal signs, tachycardia, dry mucous membranes, poor skin turgor, hypotension, and, in severe cases, shock
1st investigation
- basic metabolic panel:
hypokalemia, hyperglycemia
More - ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
- ABG:
metabolic acidosis
More
Primary aldosteronism
History
age 20 to 70 years, nocturia, polyuria, lethargy, mood disturbance, paresthesia, muscle cramps/weakness, palpitations
Exam
hypertension
1st investigation
- basic metabolic panel:
hypokalemia
- urine electrolytes and creatinine:
urine potassium >20 mEq/L
More - ECG:
normal or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More - plasma renin activity (PRA):
abnormally low (usually <1 nanogram/mL/hour)
More
Other investigations
- plasma aldosterone concentration (PAC):
abnormally high
More - PAC:PRA ratio:
>30 to 50 (normal ratio is between 4 and 10)
- aldosterone suppression test:
urine aldosterone excretion >14 microgram/24 hours during adequate sodium loading (24-hour urine sodium excretion >200 mEq)
More - CT or MRI of adrenal glands:
may be normal or may reveal typical hypodense unilateral macroadenoma (>1 cm) in a young patient
More - 24-hour urinary potassium:
inappropriate potassium wasting (defined as more than 30 mEq/day in a patient with hypokalemia)
More - adrenal venous sampling:
aldosterone production lateralizes to one adrenal in unilateral forms (e.g., aldosterone-producing adenoma or carcinoma, unilateral adrenal hyperplasia); production is bilateral in bilateral forms (mainly bilateral adrenal hyperplasia)
Exercising in a hot climate
History
running/exercise in hot climate
Exam
evidence of profuse sweating
1st investigation
- basic metabolic panel:
hypokalemia
- urine electrolytes and creatinine:
urine potassium <20 mEq/L
More - ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
Stress response in critical illness
History
history of chest pain, fever, infection, sepsis, exercise
Exam
findings dependent on cause
1st investigation
Other investigations
Uncommon
Villous adenoma
History
history of colon polyps, hematochezia, diarrhea, constipation, flatulence
Exam
may be no findings; may be bleeding or palpable mass on rectal examination; may be signs of obstruction of either the small bowel or biliary tract
1st investigation
- basic metabolic panel:
hypokalemia
- urine electrolytes and creatinine:
urine potassium <20 mEq/L, urine chloride <20 mEq/L
More - ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
- colonoscopy or barium enema:
polyp
VIPoma
History
abdominal pain, flushing, lethargy, nausea, vomiting, muscle weakness, and muscle cramps
Exam
weight loss, palpable mass
1st investigation
- basic metabolic panel:
hypokalemia
- urine electrolytes and creatinine:
urine potassium <20 mEq/L
More - ECG:
normal or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
- stool osmolar gap:
<50 mOsm/kg
More - abdominal CT scan:
most pancreatic VIPomas are >3 cm at presentation, and can usually be identified by CT
More - radiolabeled pentetreotide scintigraphy:
many pancreatic endocrine tumors have high concentrations of somatostatin receptors and can therefore be imaged with a radiolabeled form of the somatostatin analog octreotide
More - endoscopic ultrasound:
high-resolution image of the pancreas and may be able to distinguish VIPomas as small as 2 to 3 mm
More
Ileal loop/conduit with ureteric implants
History
history of genitourinary surgery with ureteric implants
Exam
nonspecific
1st investigation
- basic metabolic panel:
hypokalemia
More - urine electrolytes and creatinine:
urine potassium >20 mEq/L
More - ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
Dialysis or plasmapheresis
History
history of end-stage renal disease and dialysis dependent; or history of plasmapheresis
Exam
nonspecific
1st investigation
- basic metabolic panel:
hypokalemia
- ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
Apparent mineralocorticoid excess
History
history of licorice use, acute alcoholic intake, or renal or liver disease; preeclampsia or hypertension of pregnancy; familial forms may present in childhood
Exam
hypertension, edema
1st investigation
- basic metabolic panel:
hypokalemia
More - plasma aldosterone:
low
- urine free cortisol/cortisone ratio:
elevated
Other investigations
Cushing syndrome
History
weight gain, history of diabetes, skin thinning, easy bruisability, amenorrhea or oligomenorrhea, infertility, and decreased libido in women; men may be impotent or have decreased libido; depression, cognitive dysfunction, and emotional lability; poor wound healing, osteoporotic fractures; headaches; polyuria and nocturia; visual problems, galactorrhea
Exam
moon face, facial plethora, supraclavicular fat pads, dorsicocervical fat pad, truncal obesity, purple striae, proximal muscle weakness, hirsutism, growth retardation (children), hypertension
1st investigation
- basic metabolic panel:
hypokalemia, elevated plasma glucose
More - urine electrolytes and creatinine:
glycosuria
More - ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More - urinary free cortisol (24-hour urinary collection):
more than 2 to 4 times upper limit of normal
More - low-dose dexamethasone suppression test:
unsuppressed level at 8 am
More - evening salivary cortisol levels:
unsuppressed level
More
Other investigations
- dexamethasone-corticotropin-releasing hormone test:
cortisol >1.4 microgram/dL (50 nanomol/L)
More
Central diabetes insipidus (DI)
History
polyuria
Exam
may have signs of trauma, pituitary surgery, or hypoxic or ischemic encephalopathy
1st investigation
- basic metabolic panel:
hypokalemia, high-normal plasma sodium concentration (>142 mEq/L)
- ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More - water restriction test:
ADH release and the urine osmolality may increase as the plasma osmolality rises
More
Other investigations
Hypomagnesemia
History
history of hypokalemia, hypocalcemia, and metabolic alkalosis
Exam
neuromuscular irritability, hyperactive deep tendon reflexes, muscle cramps, muscle fibrillation, Trousseau and Chvostek signs, CNS hyperexcitability, irritability/combativeness, disorientation, psychosis, ataxia, vertigo, nystagmus, seizures (at levels <1 mEq/L)
1st investigation
- basic metabolic panel:
hypokalemia
More - ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More - serum magnesium:
low (<1.5 mEq/L)
More - serum calcium:
serum calcium may be low
More
Other investigations
Hypokalemic periodic paralysis
History
may be a recent history of exercise, stress, or conditions associated with increased release of epinephrine, cortisol, aldosterone, or insulin, if associated with hyperthyroidism there is heat intolerance, weight loss, sweating, palpitations, tremor, irritability
Exam
episodes of muscle weakness, paralytic episodes, arrhythmias: if associated with thyrotoxicosis - tachycardia, wide pulse pressure, cardiac flow murmur, thyroid enlargement, thyroid bruit, tremor
1st investigation
- basic metabolic panel:
hypokalemia
More - ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More - thyroid stimulating hormone:
variable; suppressed when hypokalemic periodic paralysis is associated with thyrotoxicosis
More
Congenital adrenal hyperplasia due to 11-beta-hydroxylase deficiency
History
may have muscle weakness, fatigue
Exam
hypertension; possible edema; features of androgen excess
1st investigation
- basic metabolic panel:
hypokalemia, metabolic alkalosis
- ECG:
normal; or may be depression of the ST segment, decrease in amplitude of T wave, increase in amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
- 11-deoxycortisol level:
elevated
- 11-deoxycorticosterone level:
elevated
Other investigations
Renal tubular acidosis (RTA)
History
previous diagnosis of type 1 (distal) or type 2 (proximal) RTA
Exam
growth retardation, kidney stones, bone disease, weakness, cardiac arrhythmias
1st investigation
- basic metabolic panel:
hypokalemia; hyperchloremia
More - urine electrolytes and creatinine:
urine potassium >20 mEq/L
More - urinanalysis and pH:
type 1 RTA: hyperchloremic acidosis with an inappropriately high urine pH (>5.5 in the presence of acidosis) plus possible hypercalciuria; type 2 RTA: bicarbonaturia, glycosuria, uricosuria, aminoaciduria, and tubular proteinuria; urinary pH >7.5
More - ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More - ABG:
metabolic acidosis (normal anion gap)
Other investigations
Bartter syndrome
History
polyuria, polydipsia[27]
Exam
growth and intellectual disability, normotension/hypotension, some patients can also have sensorineural deafness
1st investigation
- basic metabolic panel:
hypokalemia
- urine electrolytes and creatinine:
elevated potassium, calcium and chloride (>100 mEq/L)
More - ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More - ABG:
metabolic alkalosis
Other investigations
Gitelman syndrome
History
cramps (which may be severe and usually involving arms and legs), severe fatigue, polyuria, nocturia[26]
Exam
growth retardation, tetany
1st investigation
- basic metabolic panel:
hypokalemia
- urine electrolytes and creatinine:
increased chloride
More - ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More - ABG:
metabolic alkalosis
Other investigations
Liddle syndrome
History
family history of hypertension
Exam
classic presentation is with hypertension, hypokalemia, and metabolic alkalosis at a young age
1st investigation
- ABG:
metabolic alkalosis
- plasma renin activity (PRA):
abnormally low
- plasma aldosterone concentration (PAC):
abnormally low
Other investigations
- genetic testing:
detection of mutations in the beta and gamma subunits of the collecting tubule sodium channel
More
Renal disease associated with Sjögren syndrome
History
history may include previous diagnosis of type 1 (distal) renal tubular acidosis, dry eyes, dry mouth, extreme tiredness, dental decay
Exam
may be red eyes, blepharitis, or corneal ulcerations, oral candidiasis and dental caries, vaginal dryness, weakness
1st investigation
- basic metabolic panel:
hypokalemia, hyperchloremia
More - urine electrolytes and creatinine:
urine potassium >20 mEq/L
More - urine analysis and pH:
hyperchloremic acidosis with an inappropriately high urine pH (>5.5 in the presence of acidosis) plus possible hypercalciuria
More - ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More - ABG:
metabolic acidosis ( normal anion gap)
Other investigations
Renal disease associated with lupus nephropathy
History
fever, fatigue, weight loss, arthralgia, previous diagnosis of type 1 (distal) renal tubular acidosis, hematuria, anemia
Exam
photosensitive malar or butterfly rash, generalized erythematous photosensitive rash, oral ulcers, alopecia, pleural friction rub, several tender and swollen joints, peripheral edema
1st investigation
- basic metabolic panel:
hypokalemia
More - urine electrolytes and creatinine:
urine potassium >20 mEq/L
More - urine analysis and pH:
proteinuria, hematuria
- ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More - ABG:
metabolic acidosis (normal anion gap)
Other investigations
Burns
History
history of burns
Exam
extensive skin loss and ulcerations
1st investigation
- basic metabolic panel:
hypokalemia
- ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
Eczema involving a large surface area
History
history of dry itchy skin, history of asthma or hay fever, or a family history of atopy
Exam
pruritic, erythematous rash with excoriations and dryness over a large surface area of the body
1st investigation
- basic metabolic panel:
hypokalemia
- ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
Psoriasis involving a large surface area
History
family history of psoriasis
Exam
plaques involving a large surface area of the skin
1st investigation
- basic metabolic panel:
hypokalemia
- ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More
Other investigations
Cystic fibrosis (CF)
History
persistent pulmonary infection, features of pancreatic insufficiency
Exam
cough, tachypnea, dyspnea, increased sputum production, weight loss, digital clubbing, nasal polyposis, steatorrhea, arthropathy
1st investigation
- basic metabolic panel:
hypokalemia
- ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More - sweat chloride test:
sweat chloride value >60 mEq/L
More
Other investigations
Primary (often psychogenic) polydipsia
History
history of psychosis, antipsychotic medication use, polyuria
Exam
nonspecific findings
1st investigation
- basic metabolic panel:
hypokalemia
- ECG:
normal; or may be depression of the ST segment, decrease in the amplitude of the T wave, increase in the amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
More - water restriction test:
rise in urine osmolality, usually to above 500 mOsmol/kg, and no response to exogenous ADH
More
Other investigations
Hypothermia
History
history of exposure to extreme cold usually occurring in winter
Exam
shivering, impaired mental state, frostbite
1st investigation
- core temperature measurement:
<95°F to 82°F (<35°C to 28°C)
- ECG:
normal; or may be depression of the ST segment, decrease in amplitude of T wave, increase in amplitude of U waves, sinus bradycardia, premature atrial and ventricular beats, paroxysmal atrial or junctional tachycardia, atrioventricular block, ventricular tachycardia or fibrillation
Other investigations
Use of this content is subject to our disclaimer