Calcium, Blood, Total and Ionized Core Lab Study and Calcium, Urine
Synonym/Acronym
Total and free calcium, Ca (total), unbound calcium (ionized), Ca++ (ionized), Ca2+ (ionized).
Rationale
Blood: To investigate various conditions, such as hypercalcemia and hypocalcemia, related to abnormally increased or decreased calcium levels. Urine: To indicate sufficiency of dietary calcium intake and rate of absorption. Urine calcium levels are also used to assess bone resorption, kidney stones, and renal loss of calcium.
A small group of studies in this manual have been identified as Core Lab Studies. The designation is meant to assist the reader in sorting the basic “always need to know” laboratory studies from the hundreds of other valuable studies found in the manual—a way to begin putting it all together.
Normal, abnormal, or various combinations of core lab study results can indicate that all is well, reveal a problem that requires further investigation with additional testing, signal a positive response to treatment, or suggest that the health status is as expected for the associated situation and time frame.
Calcium is an essential mineral, coagulation factor, and electrolyte. Calcium is included in the bone-joint profile, basic metabolic panel (BMP), comprehensive metabolic panel (CMP), and renal panel. Panels are used as general health and targeted screens to identify or monitor conditions such as bone disease, diabetes, endocrine disorders (e.g., involving the parathyroid glands), hypertension, kidney disease, liver disease, or malnutrition.
Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction. For urine studies, usually a 24-hr urine collection is ordered. As appropriate, provide the required urine collection container and specimen collection instructions.
Normal Findings
Method: Spectrophotometry for total calcium; ion-selective electrode for ionized calcium.
Blood: Calcium, Total
| Age | Conventional Units | SI Units (Conventional Units × 0.25) |
|---|
| Cord | 9–11.5 mg/dL | 1.9–2.6 mmol/L | | Less than 12 mo | 9–10.6 mg/dL | 2.3–2.6 mmol/L | | 1–17 yr | 8.8–10.8 mg/dL | 2.2–2.7 mmol/L | | Adult | 9–10.5 mg/dL | 2.2–2.6 mmol/L | | Older adult | 8.8–10.2 mg/dL | 2.2–2.6 mmol/L |
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Blood: Calcium, Ionized
| Age | Conventional Units | SI Units (Conventional Units × 0.25) |
|---|
| Whole blood | | | | 0–11 mo | 4.2–5.84 mg/dL | 1.05–1.46 mmol/L | | 1 yr–adult | 4.6–5.08 mg/dL | 1.15–1.27 mmol/L | | Plasma | | | | Adult | 4.12–4.92 mg/dL | 1.03–1.23 mmol/L | | Serum | | | | 1–18 yr | 4.8–5.52 mg/dL | 1.2–1.38 mmol/L | | Adult and older adult | 4.64–5.28 mg/dL | 1.16–1.32 mmol/L |
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Urine: Calcium
| Age | Conventional Units* | SI Units (Conventional Units × 0.025)* |
|---|
| Infant and child | Up to 6 mg/kg per 24 hr | Up to 0.15 mmol/kg per 24 hr | | Adult on average diet | 100–300 mg/24 hr | 2.5–7.5 mmol/24 hr |
*Values depend on diet. |
Blood: Calcium, Total
- Less than 7 mg/dL (SI: Less than 1.8 mmol/L)
- Greater than 12 mg/dL (SI: Greater than 3 mmol/L) (some patients can tolerate higher concentrations)
Blood: Calcium, Ionized
Consideration may be given to verification of critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory or retesting using a rapid point-of-care testing instrument at the bedside, if available.
Observe the patient for symptoms of critically decreased or elevated calcium levels. Hypocalcemia is evidenced by convulsions, nervousness, dysrhythmias, changes in electrocardiogram (ECG) in the form of prolonged ST segment and Q-T interval, facial spasms (positive Chvostek sign), tetany, lethargy, muscle cramps, numbness in extremities, tingling, and muscle twitching (positive Trousseau sign). Possible interventions include seizure precautions, increased frequency of ECG monitoring, and administration of calcium or magnesium.
Severe hypercalcemia is manifested by excessive thirst, polyuria, constipation, changes in ECG (shortened QT interval due to shortening of the ST segment and prolonged PR interval), lethargy, confusion, muscle weakness, joint aches, apathy, anorexia, headache, nausea, and vomiting; ultimately, severe hypercalcemia may result in coma. Possible interventions include the administration of normal saline and diuretics to speed up dilution and excretion or administration of calcitonin or steroids to force the circulating calcium into the cells.
Study type: Blood collected in a gold-, red-, red/gray-top tube, or green-top [heparin] tube; Urine from an unpreserved random or timed specimen collected in a clean plastic collection container; related body system: Circulatory, Circulatory/Hematopoietic, Digestive, Endocrine, Musculoskeletal, Nervous, and Urinary systems.
Calcium, the most abundant cation in the body, participates in almost all of the body’s vital processes. Calcium concentration is largely regulated by the parathyroid glands, which secrete parathyroid hormone and by the action of vitamin D. Of the body’s calcium reserves, 98% to 99% is stored in the teeth and skeleton. Calcium values are higher in children because of growth and active bone formation.
About 45% of the total amount of blood calcium circulates as free ions that participate in numerous regulatory functions, including bone development and maintenance, blood coagulation, transmission of nerve impulses, activation of enzymes, stimulation of the glandular secretion of hormones, and control of skeletal and cardiac muscle contractility. The remaining calcium is bound to circulating proteins (40% bound mostly to albumin) and anions (15% bound to anions such as bicarbonate, citrate, phosphate, and lactate) and plays no physiological role. Together, the minerals calcium, magnesium, and phosphorus account for 98% of the body’s mineral content.
Assuming sufficient dietary intake of phosphorus, calcium, and vitamin D, three homeostatic mechanisms involving PTH and vitamin D help regulate calcium and phosphate levels by promoting:
- Intestinal absorption of calcium and phosphorus (direct effect by activated vitamin D)
- Reabsorption of calcium and excretion of phosphorus by the kidney (requires activation of vitamin D by PTH)
- Mobilization of calcium and phosphorus stores from bone tissue (requires activation of vitamin D by PTH)
Analyzing urinary phosphorus levels can provide important clues to the functioning of the kidneys and other major organs. Tests for phosphorus in urine usually involve timed urine collections over a 12- or 24-hr period. Measurement of random specimens may also be requested.
The most common cause of hypocalcemia is hypoalbuminemia. Hypercalcemia is identified when the calcium level is above normal on at least three separate measurements. The most common causes of hypercalcemia are hyperparathyroidism and cancer (with or without bone metastases).
Interrelationships:
- Calcium values can be adjusted up or down by 0.8 mg/dL (0.2 mmol/L) for every 1 g/dL (10 g/L) that albumin is greater than or less than 4 g/dL (40 g/L).
- Calcium levels are inversely proportional to parathyroid hormone (PTH) levels.
- Calcium and magnesium have similar metabolic functions and the processes of absorption (intestinal) and excretion (renal) are interdependent.
- Calcium and phosphorus have an inverse relationship with respect to concentration; serum phosphorus is increased when serum calcium is decreased.
- Normal calcium with an abnormal phosphorus value indicates impaired calcium absorption (possibly related to altered levels or activity of parathyroid hormone or vitamin D).
- Normal calcium with an elevated urea nitrogen value indicates possible hyperparathyroidism (primary or secondary).
- Normal calcium with decreased albumin value is an indication of hypercalcemia.
- Vitamin D enhances gastrointestinal (GI) absorption of calcium and phosphorus; values may vary seasonally with seasonal variations in vitamin D.
Fluid and electrolyte imbalances are often seen in patients with serious illness or injury; in these clinical situations, the normal homeostatic balance of the body is altered. During surgery or in the case of a critical illness, bicarbonate, phosphate, and lactate concentrations can change dramatically. Therapeutic treatments may also cause or contribute to electrolyte imbalance. This is why total calcium values can sometimes be misleading. Abnormal total calcium levels are used to indicate general malfunctions in various body systems. Compared to total calcium level, ionized calcium is a better measurement of calcium metabolism and functional activity. Ionized calcium levels are not influenced by protein concentrations, as seen in patients with hypoalbuminemia, chronic kidney disease, nephrotic syndrome, malabsorption, and multiple myeloma. Levels are also not affected in patients with metabolic acid-base balance disturbances. Elevations in ionized calcium may be seen when the total calcium is normal. Measurement of ionized calcium is useful to monitor patients undergoing cardiothoracic surgery or organ transplantation. It is also useful in the evaluation of patients in cardiac arrest.
Regulating electrolyte balance is a major function of the kidneys. In normally functioning kidneys, urine levels increase when serum levels are high and decrease when serum levels are low to maintain homeostasis. Analyzing urinary electrolyte levels can provide important clues to the functioning of the kidneys and other major organs. Tests for calcium in urine usually involve timed urine collections during a 12- or 24-hr period. Measurement of random specimens may also be requested. Urinary calcium excretion may also be expressed as calcium-to-creatinine ratio: In a healthy individual with constant muscle mass, the ratio is less than 0.14.
Summary of significant electrolytes/minerals (Note: Bicarbonate HCO3– is not a mineral)
| Intracellular | Extracellular | | Cation (+) Positive | Anion (-) Negative | Cation (+) Positive | Anion (-) Negative | | K+ Potassium is the major intracellular cation | PO4 3- Phosphate is the major intracellular anion | Na+ Sodium is the major extracellular cation | Cl- Chloride is the major extracellular anion | | Mg2+ (Magnesium) | | Ca2+ (Calcium) | HCO3- Bicarbonate is the second most important extracellular anion |
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Factors That May Alter the Results of the Study
Blood
- Drugs and other substances that may increase calcium levels include anabolic steroids, some antacids (alkaline), calcium salts, corticosteroids (prednisone), furosemide, hydralazine, hydrochlothiazide, isotretinoin, lithium, mannitol, metolazone, oral contraceptives, parathyroid hormone, progesterone, spironolactone, tamoxifen, thyroid hormone, triamterene, vitamin analogs (calcitrol, ergocalciferol), and vitamins (A and D).
- Specimens should never be collected above an IV line because of the potential of contaminating the sample with the substance of interest, if it is present in the IV solution, falsely increasing the result.
- Hemolysis may cause falsely increased results.
- Patients who ingest large amounts of milk, calcium or vitamin D supplements, or antacid tablets shortly before specimen collection will have increased calcium values.
- Venous hemostasis caused by prolonged use of a tourniquet during venipuncture can falsely elevate calcium levels.
- Drugs and other substances that may decrease calcium levels include acetazolamide, acetylsalicylic acid, albuterol, alprostadil, asparaginase, calcitonin, carbamazepine, chlorthalidone, chlorothiazide, cisplatin, citrates, corticocorticoids, denosumab, estrogens, foscarnet, gastrin, gentamicin, glucagon, glucose, heparin, insulin, laxatives (excessive use), magnesium salts, hydrochlorothiazide, methicillin, oral contraceptives, phenobarbital, phenytoin, plicamycin, phosphates, tetracycline, theophylline, tobramycin, trazodone, and viomycin.
- Specimens should never be collected above an IV line because of the potential for dilution when the specimen and the IV solution combine in the collection container, falsely decreasing the result.
- Patients on ethylenediaminetetra-acetic acid (EDTA) therapy (chelation) may show falsely decreased calcium values.
- Patients receiving massive blood transfusions may experience decreased ionized calcium values related to chelation of the free calcium by the anticoagulant in the blood products.
- Patients with chronic kidney disease, especially those on hemodialysis, may have low calcium levels. The inability of the kidneys to filter excess phosphorus from the blood into urine stimulates abnormal excretion of calcium, resulting in lower circulating calcium levels. If the calcium concentration in the dialysate fluid is not adjusted to correct the blood levels, the parathyroid glands secrete PTH, which causes calcium to be lost from the bones. Over time, bone loss results in deformities and loss of function.
- Patients with low albumin levels (e.g., in cases of malnutrition or dilutional effect of IV fluid excess) will have low total calcium levels.
Urine
- Drugs and other substances that can increase urine calcium levels include acetazolamide, ammonium chloride, asparaginase, calcitonin, corticosteroids (corticotropin, dexamethasone, prednisolone, triamcinolone), ethacrynic acid, mannitol (initially), meralluride, mercaptomerin, metolazone, parathyroid hormone, plicamycin, sulfates, torsemide, triamterene, vitamin D/vitamin D analogs (dihydroxycholecalciferol, ergocalciferol), and viomycin.
- Drugs and other substances that can decrease urine calcium levels include angiotensin, bicarbonate, calcitonin, cellulose phosphate, citrates, lithium, mestranol, methyclothiazide, neomycin, oral contraceptives, spironolactone, thiazides, and vitamin K.
- All urine voided for the timed collection period must be included in the collection or else falsely decreased values may be obtained. Compare output records with volume collected to verify that all voids were included in the collection.
Other Considerations
- Calcium exhibits diurnal variation; serial blood samples should be collected at the same time of day for comparison.
- All urine voided for the timed collection period must be included in the collection or falsely decreased values may be obtained. Compare output records with volume collected to verify that all voids were included in the collection.
Potential Nursing Problems: Assessment & Nursing Diagnosis
| Problems | Signs and Symptoms |
|---|
| Airway (related to hypocalcemia—laryngospasam; inadequate calcium intake; hypoparathyrodism; pancreatic insufficiency) | Dyspnea, increased work of breathing, altered respiratory rate and pattern, restlessness, increased sputum, cyanosis, cool extremities, adventitious and diminished breath sounds | | Health management(related to hypocalcemia—failure to regulate diet, lack of exercise, alcohol use, smoking; or related to hypercalcemia—familial hypocalciuric hypercalcemia; imobility; excessive calcium supplement intake; vitamin D toxicity) | Inability or failure to recognize or process information toward improving health and preventing illness with associated mental and physical effects, refusal to adhere to therapeutic medical management for calcium excess or deficit | | Injury risk related to hypercalcemia—bone demineralization; hyperparathyroidism; malignancy; excessive calcium supplement intake; vitamin D toxicity; renal failure; thiazide diuretics; metabolic acidosis | Lethargy, muscle weakness, decreased muscle tone, confusion, personality changes, memory impairment, hallucinations, slurred speech, maliase, kidney stones, cardiac irregularities, poor skin turgor | | Injury risk related to hypocalcemia—(hypoparathryoidism; low albumin; pancreatitis; thyroidectomy; inadequate calcium resorption; acute kidney injury, chronic kidney disease, or failure; lack of dietary vitamin D; decreased sun exposure; eating disorders) | Tingling and numbness in the fingertips and around the mouth, muscle cramps, tetany, seizures, confusion, bone pain, weakness, unsteady gait, laryngospasm, cardiac dysrhythmias, hyperactive tendon reflexes, twitching, muscular irritability, Chvostek and Trousseau signs | | Nutrition (insufficient—excessive diarrhea; bowel resection; laxative abuse; drugs such as loop diuretics, antimicrobials, antineoplastic; caffeine; alcohol; related to inability to digest, metabolize, ingest foods; refusal to eat; increased metabolic needs associated with disease process; lack of understanding; inability to obtain healthy foods) | Unintended weight loss; pale, dry skin; dry mucous membranes; documented inadequate caloric intake; subcutaneous tissue loss; hair pulls out easily; paresthesia; brittle nails; dental changes; psoriasis and eczema exacerbation | | Nutrition (excess—excessive calcium supplement intake; vitamin D toxicity; increased dietary calcium intake; hyperparathyroidism) | Hypoactive bowel; paralytic ileus, abdominal distention, excessive thirst, nausea, vomiting, constipation, dehydration, poor skin turgor | | Pain (related to hypercalcemia—bone pain, muscle weakness; kidney stones; abdominal pain; or related to hypocalcemia—tetany; muscle spasms; abdominal cramps; laryngospasam) | Emotional symptoms of distress, crying, agitation, facial grimace, moaning, verbalization of pain, rocking motions, irritability, disturbed sleep, diaphoresis, altered blood pressure and heart rate, nausea, vomiting, self-report of pain | | Airway (related to hypocalcemia—laryngospasam; inadequate calcium intake; hypoparathyrodism; pancreatic insufficiency) | Dyspnea, increased work of breathing, altered respiratory rate and pattern, restlessness, increased sputum, cyanosis, cool extremities, adventitious and diminished breath sounds |
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Before the Study: Planning and Implementation
Teaching the Patient What to Expect
- Discuss how this test can assist as a general indicator in diagnosing health concerns and in evaluating the effectiveness of the body’s absorption of calcium.
- Explain that a blood or urine sample is needed for the test. Information regarding urine specimen collection is presented with other general guidelines in Appendix A: Patient Preparation and Specimen Collection.
Potential Nursing Actions
- Include on the collection container’s label urine total volume, test start and stop times/dates, and any medications that may interfere with test results.
After the Study: Implementation & Evaluation Potential Nursing Actions
Treatment Considerations
Airway
- Assess respiratory status, monitor oxygen saturation, administer ordered oxygen and prepare for possible intubation and mechanical ventilation.
- Administer medications ordered to treat hypocalcemia.
- Monitor and trend serum Ca levels.
- Facilitate culturally appropriate diet changes that include calcium-rich foods.
- Facilitate adherence to taking oral calcium supplements.
Health Management
- Encourage regular participation in weight-bearing exercises.
- Assess diet, smoking, and alcohol use.
- Discuss importance of adequate calcium intake with diet and supplements and the dangers of calcium overuse and vitamin D toxicity.
- Refer to smoking cessation and alcohol treatment programs.
- Collaborate with HCP for bone density evaluation.
Injury Risk
- Facilitate management of hypercalcemia.
- Assess for signs and symptoms of hypercalcemia.
- Facilitate interventions designed to reduce serum calcium levels.
- Administer ordered fluids to increase fluid volume which will in turn increase renal excretion of calcium.
- Facilitate a low-calcium diet; elimination of medications/vitamins/organics containing calcium.
- Facilitate discontinuance of thiazide, diuretics, lithium as they limit calcium excretion.
- Note that malignancy may require surgery, chemotherapy, radiation therapy or a combination of these to decrease serum calcium.
- Encourage activity and range of motion exercises, or turn frequently to prevent urinary stasis with stone formation and bone loss.
- Utilize safety precautions for those who become confused, provide frequent orientation, and facilitate a safe environment to decrease fall and injury risk.
Injury Risk
- Facilitate management of hypocalcemia.
- Assess for signs and symptoms of hypocalcemia.
- Monitor and trend calcium and phosphorus levels.
- Administer ordered calcium replacement therapy.
- Assess for bone pain and alterations in mobility.
- Increase dietary calcium and encourage the minimum recommended sun exposure.
Pain
- Collaborate with the patient and HCP to identify the best pain management modality to provide relief.
- Refrain from activities that may aggravate pain.
- Use the application of heat or cold to the best effect in managing the pain.
- Monitor pain severity and effectiveness of pain management strategies.
- Make changes in pain management strategies based on effectiveness assessment.
Nutritional Considerations
General
- Complete an accurate daily weight at the same time each day with the same scale.
- Obtain an accurate nutritional history.
- Assess swallowing ability.
- Assess attitude toward eating.
- Discuss the importance of adequate dietary calcium intake to maintain health.
- Promote a dietary consult to evaluate current eating habits and best method of nutritional supplementation.
- Develop short-term and long-term eating strategies.
- Monitor and trend nutritional laboratory values such as albumin, Hgb, iron, RBC count, WBC count, and serum electrolytes.
- Discourage caffeinated and carbonated beverages.
- Encourage cultural home foods.
- Provide a pleasant environment for eating.
- Explain how good oral hygiene prior to eating can improve the food’s flavor.
- Alter food seasoning to enhance flavor. Provide parenteral or enteral nutrition as prescribed.
Deficient Calcium
- Discuss how daily intake of calcium is important even though body stores in the bones can be called on to supplement circulating levels.
- Discuss that dietary calcium can be obtained from animal or plant sources: almonds (milk, nuts), beet greens, broccoli, cheese, clams, kale, legumes, milk and milk products, oysters, rhubarb, salmon (canned), sardines (canned), spinach, tofu, yogurt, and calcium-fortified foods such as orange juice are high in calcium.
- Explain that milk and milk products also contain vitamin D and lactose, which assist calcium absorption.
Excess Calcium
- Discuss importance of drinking fluids containing sodium.
- Avoid calcium-rich foods.
- Increase dietary bulk to prevent constipation.
Clinical Judgement
- Consider how to frame a convincing message toward moderation or initiation of taking supplemental vitamins.
Follow-Up and Desired Outcomes
- Acknowledges the value of contact information provided for the U.S. Department of Agriculture’s resource for nutrition (www.choosemyplate.gov).
- Understands the signs and symptoms associated with a calcium imbalance.
- Recognizes the importance of associated studies such as ECG, phosphorus, and albumin so the correct therapeutic measures can be taken.
- Agrees to meet with a speech therapist to evaluate swallowing ability, as appropriate.
- Accurately demonstrates how to perform a daily self-weight and to record the results correctly.
- Understands that parenteral or enteral nutrition may be used if oral intake is insufficient to support caloric needs.
- Adheres to the request to take prescribed calcium replacement therapy and can accurately self-administer prescribed dietary supplements.
- Those with excess or deficient calcium levels agree to adhere to therapeutic interventions to promote improved symptom control, safety, fluid and electrolyte balance, mobility, and neurological/cognitive homeostasis.