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Introduction ⬇

Calcium (Ca) homeostasis is maintained by the parathyroid hormone. The bulk of calcium excreted is eliminated in the stool. However, a small quantity of calcium is normally excreted in the urine. This amount varies with the quantity of dietary calcium ingested. Increased calcium in urine results from an increase in intestinal calcium absorption, a lack of renal tubule reabsorption of calcium, resorption or loss of calcium from bone, or a combination of these mechanisms. Values in both healthy and sick persons have a wide range.

The urine calcium test is used for evaluation of calcium intake and/or the rate of intestinal absorption, bone resorption, and kidney loss. Urine calcium is high in 30%–80% of cases of primary hyperparathyroidism but does not reliably diagnose this disease.

Normal Findings ⬆ ⬇

Normal diet: 100–300 mg/24 hr or 2.50–7.50 mmol/d

Low-calcium diet: 50–150 mg/24 hr or 1.25–3.75 mmol/d

Rate of calcium excretion can be expressed as the ratio of calcium/creatinine (Ca/Cr).

Ca (mg/dL)/Cr (mg/dL): <0.14 or Ca (mmol/L)/Cr (mmol/L) <0.40

Procedure ⬆ ⬇

  1. Properly label a 24-hour urine container with the patient’s name, date and time of collection, and test(s) ordered.

  2. Procure an acid-washed bottle. See Table 3.3 regarding 24-hour urine collection data.

  3. Follow general instructions for 24-hour urine collection (see Long-Term, Timed Urine Specimen [2-Hour, 24-Hour]). Refrigerate during collection.

  4. Record exact starting and ending times of the collection on the specimen container and in the patient’s healthcare record.

  5. Send the specimen to the laboratory when collection is completed.

  6. Perform a random (Sulkowitch) test in an emergency. Follow directions for random urine collection.

Clinical Implications ⬆ ⬇

  1. Increased urine calcium (hypercalciuria: >350 mg/24 hr or >8.75 mmol/d) is found in:

    1. Hyperparathyroidism (30%–80% of cases)

    2. Sarcoidosis

    3. Primary cancers of breast and bladder

    4. Osteolytic bone metastases (carcinoma, sarcoma)

    5. Multiple myeloma

    6. Paget disease

    7. Renal tubular acidosis

    8. Fanconi syndrome

    9. Vitamin D intoxication

    10. Idiopathic hypercalciuria

    11. Osteoporosis (especially after immobilization)

    12. Osteitis deformans

    13. Thyrotoxicosis

  2. Increased urinary calcium almost always accompanies increased blood calcium levels.

  3. Calcium excretion levels greater than calcium intake levels are always excessive; urine excretion values >400–500 mg/24 hr (>10–12.5 mmol/d) are reliably abnormal.

  4. Increased calcium excretion occurs whenever calcium is mobilized from the bone, as in metastatic cancer or prolonged skeletal immobilization.

  5. When calcium is excreted in increasing amounts, the situation creates the potential for nephrolithiasis or nephrocalcinosis, especially with high protein intake.

  6. Decreased urine calcium is found in:

    1. Hypoparathyroidism

    2. Familial hypocalciuric hypercalcemia

    3. Vitamin D deficiency

    4. Preeclampsia

    5. Acute nephrosis, nephritis, kidney disease

    6. Renal osteodystrophy

    7. Vitamin D–resistant rickets

    8. Metastatic carcinoma of prostate

    9. Malabsorption syndrome—celiac disease (sprue), steatorrhea

  7. Urine calcium decreases late in normal pregnancy.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain purpose of test, procedure for urine collection, and interfering factors. Written instructions can be helpful.

  2. Encourage food and fluids.

  3. If the urine calcium test is done because of a metabolic disorder, the patient should eat a low-calcium diet, and calcium medications should be restricted for 1–3 days before specimen collection.

  4. For a patient with a history of kidney stone formation, urinary calcium results will be more meaningful if the patient’s usual diet is followed for 3 days before specimen collection. Do not stop medications.

  5. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings. Monitor accordingly for calcium imbalances.

  2. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Clinical Alert

  1. Observe patients with very low urine calcium levels for signs and symptoms of tetany (muscle spasms, twitching, hyperirritable nervous system).

  2. The first sign of calcium imbalance may be pathologic fracture that can be related to calcium excess.

  3. The Sulkowitch test (random urine sample) can be used in an emergency, especially when hypercalcemia is suspected because hypercalcemia is life-threatening.

Interfering Factors ⬆

  1. Falsely elevated levels may be caused by:

    1. Some drugs (e.g., calcitonin; vitamins A, K, and C; and corticosteroids) (see Appendix E)

    2. Urine procured immediately after meals in which high calcium intake has occurred (e.g., milk)

    3. Increased exposure to sunlight

    4. Immobilization (especially in children)

  2. Falsely decreased levels may be found with:

    1. Increased ingestion of phosphate, bicarbonate, antacids

    2. Alkaline urine

    3. Thiazide diuretics (can be used to lower calcium levels therapeutically)

    4. Oral contraceptives, estrogens

    5. Lithium (see Appendix E)