Updated: 3/7/2019

Acid-Base Differential Diagnosis

Review Topic
  • Acid-base disorders are commonly seen throughout medicine 
    • acidosis results in an abnormally elevated H+ concentration in the blood (thus called acidemia)
    • alkalosis results in an abnormally decreased H+ concentration in the blood (thus called alkalemia)
  • These acid-base disorders may be caused by
    • a primary disturbance in HCO3- resulting in a metabolic acidosis or alkalosis
    • a primary disturbance in PCO2 resulting in a respiratory acidosis or alkalosis
  • Simple acid-base disorders
    • blood pH abnormalities caused by one acid base disorder
    • metabolic acidosis
      • due to a decrease in blood HCO3-
        • secondary to impaired H+ excretion, fixed H+ ingestion, or increased H+ production
          • look at "anion gap" below
    • metabolic alkalosis
      • due to an increase in blood HCO3-
        • secondary to increased HCO3- intake or loss of fixed H+
          • loop diuretics (e.g., furosemide)
          • vomiting and nasogastric tube suction
          • antacid use
          • hyperaldosteronism
          • laxative abuse
            • mild abuse results in alkalosis due to hypokalemia and the resulting shift of H+ into the cells
            • if abuse is severe, metabolic acidosis results due to the excessive diarrhea and loss of HCO3-
    • respiratory acidosis
      • due to an increase in PCO2
        • due to hypoventilation
          • airway obstruction (e.g., epiglottitis)
          • acute lung disease
          • chronic lung disease
          • opioids and sedatives
          • respiratory muscle weakness
    • respiratory alkalosis
      • due to a decrease in PCO2
        • due to hyperventilation
          • normal pregnancy
          • hysteria
          • hypoxemia (e.g., high altitude)
          • salicylates (early)
          • pulmonary embolism
          • pneumonia
  • Anion gap
    • under normal conditions, anions and cations are equal to each other within any body fluid compartment (e.g., plasma)
      • the major cation that is measured is Na+
      • the major anions that are measured is HCO3- and Cl-
      • because there is more Na+ than HCO3- and Cl- there are unmeasured anions that allow us to achieve electroneutrality
        • unmeasured plasma anions include plasma proteins, citrate, phosphate, and sulfate
      • anion gap = Na+ - (Cl- + HCO3-)
        • normal = 8-16 mEq/L
    • anion gap is very useful for narrowing the differential diagnosis of metabolic acidosis
      • normal anion gap metabolic acidosis (also called hyperchloremic metabolic acidosis with a normal anion gap) 
        • Hyperalimentation
        • Addison's disease
        • Renal tubular acidosis
        • Diarrhea
        • Acetazolamide
        • Spironolactone
        • Saline infusion
        • mnemonic: HARDASS
      • elevated anion gap metabolic acidosis
        • Methanol (formic acid)
        • Uremia
        • Diabetic ketoacidosis
        • Propylene glycol
        • Iron tablets or isoniazid
        • Lactic acidosis (such as by metformin toxicity) 
        • Ethylene glycol
        • Salicylates (late)
        • mnemonic: MUDPILES

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Questions (9)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2

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(M1.RL.8) A 66-year-old man is brought to the emergency department by his daughter because of 3 days of fever, chills, cough, and shortness of breath. The cough is productive of yellow sputum. His symptoms have not improved with rest and guaifenesin. His past medical history is significant for hypertension, for which he takes hydrochlorothiazide. He has a 30-pack-year history of smoking. His temperature is 38.9 C (102.0 F), blood pressure 88/56 mm Hg, and heart rate 105/min. Following resuscitation with normal saline, his blood pressure improves to 110/70 mm Hg. His arterial blood gas is as follows:

Blood pH 7.52, PaO2 74 mm Hg, PaCO2 28 mm Hg, and HCO3- 21 mEq/L.

Which of the following acid-base disturbances best characterizes this patient's condition? Review Topic

QID: 104282

Normal acid-base status




Metabolic acidosis




Metabolic alkalosis




Respiratory acidosis




Respiratory alkalosis




Select Answer to see Preferred Response

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(M1.RL.21) A 35-year-old patient with a history of diabetes presents to the ED with a myriad of systemic complaints. An arterial blood gas shows serum pH = 7.3, HCO3- = 13 mEq/L, PCO2 = 27 mmHg. Which of the following would you LEAST expect to observe in this patient? Review Topic

QID: 100975

Increased anion gap




Increased serum ketones




Increased urine output




Decreased respiratory rate




Increased serum potassium




Select Answer to see Preferred Response

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