eMedicine Specialties > Nephrology > Acid-Base, Fluid, and Electrolyte Disorders

Hypocalcemia: Differential Diagnoses & Workup

Author: Manish Suneja, MD, Assistant Professor, Department of Internal Medicine, Division of Nephrology, University of Iowa Hospitals and Clinics
Coauthor(s): Heather A Muster, MD, MS, Assistant Professor, Division of Nephrology, University of Iowa
Contributor Information and Disclosures

Updated: Aug 25, 2009

Differential Diagnoses

Acute Renal Failure
Hypomagnesemia
Anorexia Nervosa
Hypoparathyroidism
Chronic Renal Failure
Metabolic Alkalosis
Hyperparathyroidism
Osteoporosis
Hyperphosphatemia
Pancreatitis, Acute
Hypoalbuminemia
Tuberculosis

Workup

Laboratory Studies

  • Serum albumin
    • In a patient with hypocalcemia, the serum albumin is essential to the diagnosis of true hypocalcemia, which involves a reduction in ionized serum calcium, or to the diagnosis of "factitious" hypocalcemia, meaning decreased total, but not ionized, calcium.
    • An estimate to correct for hypoalbuminemia is to subtract 0.8 mg/dL from the total serum calcium for each 1.0-g/dL decrease in albumin below 4.0 g/dL.
  • Serum ionized calcium: Ionized calcium is the definitive method to help diagnose hypocalcemia.
  • Serum phosphorus
    • In healthy kidneys, PTH stimulates phosphate excretion. A patient with hypocalcemia and elevated phosphorus levels suggests hypoparathyroidism, pseudohypoparathyroidism, or magnesium depletion (occasionally). Hypophosphatemia most frequently is associated with the latter, which is caused by nutritional deficiencies.
    • Patients with renal failure and hypocalcemia usually present with hyperphosphatemia and high PTH levels.
    • Hypophosphatemia develops in patients with vitamin D deficiency and hungry bone disease.
  • Parathyroid hormone levels: Low-to-normal PTH levels occur in patients with hereditary or acquired hypoparathyroidism and in patients with severe hypomagnesemia; however, patients with ineffective PTH have elevated PTH levels. The PTH elevation is a result of hypocalcemia.
  • Serum magnesium: The serum magnesium level always should be checked to determine its potential contribution to the hypocalcemia.
  • Vitamin D metabolites
    • If vitamin D deficiency is suspected, measurements of 25(OH) D and 1,25(OH)2 D should be performed.
    • Measurement of a low 25(OH) D level suggests vitamin D deficiency from poor nutritional intake, lack of sunlight, or malabsorption.
    • Low levels of 1,25(OH)2 D in association with high PTH suggest ineffective PTH from a lack of vitamin D, as observed in patients with chronic renal failure, vitamin D–dependent rickets type I (VDDR-I), and pseudohypoparathyroidism.
    • Urinary cAMP may help to differentiate hypoparathyroidism from pseudohypoparathyroidism types I and II.
  • Alkaline phosphatase: In patients with PTH deficiencies, alkaline phosphatase levels tend to be normal or slightly decreased. On the other hand, these levels frequently are elevated in patients with osteomalacia and rickets.

Imaging Studies

  • Skeletal radiograms
    • Disorders associated with rickets or osteomalacia present with the pathognomonic Looser zones, better observed in the pubic ramus, upper femoral bone, and ribs.
    • Osteoblastic metastases from certain tumors (eg, breast, prostate, lung) can cause hypocalcemia.
  • Computed tomography (CT) scans of the head may show basal ganglia calcification and extrapyramidal neurologic symptoms (in idiopathic hypoparathyroidism).

Other Tests

  • Electrocardiogram (ECG): Hypocalcemia leads to a prolonged QT interval and severe ST abnormalities (see image below and Image 1).

Electrocardiogram (ECG) findings in severe hypoca...

Electrocardiogram (ECG) findings in severe hypocalcemia.

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Electrocardiogram (ECG) findings in severe hypoca...

Electrocardiogram (ECG) findings in severe hypocalcemia.

Procedures

  • Bone biopsy: If the diagnosis of osteomalacia is suspected, a bone biopsy can determine the final diagnosis.

More on Hypocalcemia

Overview: Hypocalcemia
Differential Diagnoses & Workup: Hypocalcemia
Treatment & Medication: Hypocalcemia
Follow-up: Hypocalcemia
Multimedia: Hypocalcemia
References
Further Reading
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Keywords

hypocalcemia, low calcium, serum calcium, hypercalcemia, vitamin D deficiency, magnesium deficiency, hypocalcemia causes, hypocalcemia symptoms, hypocalcemia treatment, serum calcium levels, calcium-sensing receptor, ionized calcium concentration, chronic renal failure, acute renal failure, acute pancreatitis, hypoparathyroidism, pseudohypoparathyroidism

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Contributor Information and Disclosures

Author

Manish Suneja, MD, Assistant Professor, Department of Internal Medicine, Division of Nephrology, University of Iowa Hospitals and Clinics
Manish Suneja, MD is a member of the following medical societies: American College of Physicians, American Society of Nephrology, and National Kidney Foundation
Disclosure: Nothing to disclose.

Coauthor(s)

Heather A Muster, MD, MS, Assistant Professor, Division of Nephrology, University of Iowa
Heather A Muster, MD, MS is a member of the following medical societies: American College of Physicians, American Society of Nephrology, American Society of Transplantation, International Society of Nephrology, Minnesota Medical Association, and National Kidney Foundation
Disclosure: Nothing to disclose.

Medical Editor

James W Lohr, MD, Fellowship Program Director, Professor, Department of Internal Medicine, Division of Nephrology, State University of New York at Buffalo
James W Lohr, MD is a member of the following medical societies: American College of Physicians, American Heart Association, American Society of Nephrology, and Central Society for Clinical Research
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Eleanor Lederer, MD, Consulting Staff, Louisville VA Hospital; Professor of Medicine; Interim Chief of Nephrology; Director of Nephrology Training Program; Director, Metabolic Stone Clinic; Director of Outpatient Clinics, Kidney Disease Program, University of Louisville School of Medicine
Eleanor Lederer, MD is a member of the following medical societies: American Association for the Advancement of Science, American Federation for Medical Research, American Society for Biochemistry and Molecular Biology, American Society for Bone and Mineral Research, American Society of Nephrology, American Society of Transplantation, International Society of Nephrology, Kentucky Medical Association, National Kidney Foundation, and Phi Beta Kappa
Disclosure: Nothing to disclose.

CME Editor

Rebecca J Schmidt, DO, FACP, FASN, Professor of Medicine, Section Chief, Department of Medicine, Section of Nephrology, West Virginia University School of Medicine
Rebecca J Schmidt, DO, FACP, FASN is a member of the following medical societies: American College of Osteopathic Internists, American College of Physicians, American Medical Association, American Society of Nephrology, International Society of Nephrology, National Kidney Foundation, Renal Physicians Association, and West Virginia State Medical Association
Disclosure: Abbott Grant/research funds Speaking and teaching; Genzyme Honoraria Consulting; Amgen Honoraria Speaking and teaching; Ortho Biotech Honoraria Speaking and teaching

Chief Editor

Vecihi Batuman, MD, FACP, FASN, Professor of Medicine, Section of Nephrology-Hypertension, Tulane University School of Medicine; Chief, Medicine Service, Southeast Louisiana Veterans Health Care System
Vecihi Batuman, MD, FACP, FASN is a member of the following medical societies: American College of Physicians, American Society of Hypertension, American Society of Nephrology, and International Society of Nephrology
Disclosure: Nothing to disclose.

 
 
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