Rules of Thumb: You always need to consider volume status when interpreting labs - volume overload ("hyperaquemia") will lead to dilution of electrolytes, making everything seem low. Similarly, volume depleted patients will seem to have elevated levels of everything. Different attendings have different levels of concern regarding electrolyte imbalances. The lists that follow are intended to give you a general idea of issues that are potentially pertinent, but they certainly aren't exhaustive - you need to think about whatever is happening with the specific patient in front of you.

Na+ (hyponatremia): nl=140. Low < 135 mEq/L. Worry < 125.
S/Sx: confusion, muscle cramps, anorexia, nausea. Severe = seizures, coma
Think: DILUTION. SIADH, renal failure, TB, diuretics, vomiting, diarrhea, hyperglycemia, third spacing, meds.
Tx: fluid restrict. 3% NS in emergencies (usually <120) (watch for central pontine myelinolysis!! <12mEq / 24hrs).

Na+ (hypernatremia): nl=140. High > 144 mEq/L. Worry > 150.
S/Sx: confusion, lethargy, seizures, coma.
Think: vomiting, diarrhea, diabetes insipidus, adrenal insufficiency, Cushing's Syndrome, diuretics, excess salt intake.
Tx: fluids (D5W). Treat underlying disorder.

K+ (hypokalemia): nl=4-4.5. Low < 3.3 mEq/L.
S/Sx: muscle weakness paralysis. Arrythmias death. EKG changes.
Think: DILUTION. ALKALOSIS. Insulin, diuretics (lasix particularly), DKA, vomiting, diarrhea.
Tx: Potassium (in the form of potassium chloride). Do not give > 40 mEq/hour!

K+ (hyperkalemia): nl=4-4.5. High > 4.9 mEq/L.
S/Sx: weakness, irritability, arrythmias, paralysis. EKG changes.
Think: ACIDEMIA. Renal insufficiency, K+ sparing diuretics, insulin deficiency, magnesium deficiency.
Tx: correct acidosis. Can give glucose and insulin. IV Ca+ in emergency. Dialysis.

Cl- (hypochloremia): nl=100.
S/Sx: No specific symptoms - generally a finding suggesting other etiology.
Think: DILUTION. CHF, SIADH, vomiting, diarrhea, DKA, Addison's disease, nephritis.
Tx: treat underlying disorder

Cl- (hyperchloremia): nl=100
S/Sx: No specific symptoms - generally a finding suggesting other etiology.
Think: dehydration, cystic fibrosis, hyperparathyroid, metabolic acidosis, chronic diarrhea, drugs
Tx: treat underlying disorder

Bicarbonate: nl=26
in METABOLIC ACIDOSIS. Also seen in respiratory alkalosis as compensatory mechanism. Seen in DKA, HONK, heat stroke. See mnemonic section for good list.
in METABOLIC ALKALOSIS. Also seen in respiratory acidosis as compensatory mechanism.

BUN (blood urea nitrogen): nl=8-18.
in liver disease, malnutrition, pregnancy, celiac disease
in GFR, renal insufficiency, drugs (antibiotics, diuretics, steroids), ATN, dehydration, GI bleeding, heat stroke, cirrhosis, pancreatitis.
Increases ~ 20-40/day in acute post-renal or intrarenal disorders.

Creatinine: nl=0.6-1.2
in muscle mass (old age, muscle wasting), pregnancy
in GFR, renal insufficiency, ATN, UTI, DKA, heat stroke, rhabdomyolysis.
Increases ~ 2-4/day in acute post-renal or intrarenal disorders.

BUN/Creatinine Ratio:
In prerenal disorders becomes >10:1.

Glucose (hypoglycemia): nl <125. nl fasting <110, >70. Low <70.
S/Sx: sweating, anxiety, tremors, tachycardia, seizures, fatigue, syncope, HA, visual changes, changes.
Think: INSULIN OVERDOSE. insulinoma, factitious (insulin or sulfonylurea use), liver or renal disease, alcohol abuse, hormone deficiency.
Tx: glucose

Glucose (hyperglycemia): nl <125. nl fasting <110, >70. High >125, >110 fasting.
DKA (typically seen in Type I):
S/Sx: nausea/vomiting, polyuria, polydipsia, abdominal pain, anorexia, drowsiness, stupor, coma, dyspnea, malaise, fruity breath odor, dehydration.
Think: poorly controlled diabetes - insufficient insulin.
Tx: fluids, insulin, replace K+ & phosphate
HONK [HyperOsmolar Non-Ketotic Coma] (typically seen in Type II):
S/Sx: changes, dehydration, seizures, polyuria, N/V
Think: poorly controlled diabetes - insufficient oral agents, insulin requiring, or insufficient insulin
Tx: fluids, low dose insulin, replace K+ Ca+ Mag and phosphorous

Ca+ (hypocalcemia): nl=
S/Sx: tetany, paresthesias, seizures, weakness, changes, arrythmias, EKG changes.
Think: Hypoalbuminemia, renal insufficiency, vitamin D deficiency, hypomag, pancreatitis. Chvostek's sign, Trousseau's sign.
Tx: replace albumin, mag, or vit D.

Ca+ (hypercalcemia): nl=
S/Sx: constipation, N/V, CNS changes, changes, myopathy, weakness, hypertension, polyuria
Think: MALIGNANCY. Hyperparathyroid, MEN syndromes, thiazides, vit D intoxication.
Tx: hydration & lasix, calcitonin, glucocorticoids, phosphates. Treat underlying cause.

Magnesium (hypomagnesemia): nl 1.8-3.0. Low <1.8 mg/dl.
S/Sx: weakness, hyperreflexia, tremors, convulsions, coma, arrythmias. hypokalemia & hypocalcemia.
Think: malabsorption, alcoholic, diarrhea, fistula, diuretics, ATN, DKA, SIADH, hyperthyroid, hyperparathyroid, drugs (digoxin, cyclosporin, amphotericin, methotrexate, antibiotics)
Tx: Magnesium, treat underlying disorder.

Magnesium (hypermagnesemia): nl 1.8-3.0. High >2.3 mg/dl
S/Sx: paresthesias, hypotension, confusion, paralysis, coma, hypocalcemia. EKG changes.
Think: GFR, endocrinopathy, DKA, pheo, antacid/laxative abuse, rhabdomyolysis.
Tx: treat underlying disorder. IV calcium gluconate for cardiac conduction abnormalities. Dialysis if severe.

Phosphate (hypophosphatemia): <2.5 mg/dl
S/Sx: proximal muscle weakness, bone pain, paresthesias, seizures, coma, ataxia, anemia, platelet dysfunction, rhabdomyolysis
Think: intake, alcoholic, malabsorption, antacids, renal dysfunction, DKA, steroids, TPN, theophyllin, hyperthermia.

Phosphate (hyperphosphatemia): >5 mg/dl
S/Sx: Same as hypocalcemia (tetany, paresthesias, seizures, weakness, changes, arrythmias, EKG changes). Also, various calcifications occur.
Think: Renal dysfunction, sickle cell anemia, chemotherapy, acidosis, rhabdomyolysis, hypoparathyroid, excessive intake.