Urine Analysis: Part 11 – Urine Calcium (Ca), (Quantitative 24 hrs urine calcium)
- 24 hours of urine is collected in the acid wash bottle.
- Add 10 to 20 mL of 6M/L HCl.
- 1 to 2 mL of a random urine sample can also be evaluated.
- Refrigerate the urine during collection.
- Or acidify the urine to pH <2.0 to dissolve the calcium salts.
- Wash the bottle with dilute HCl and then rinse with water.
- Avoid contamination with calcium.
- Don’t use cork because they may contaminate the urine.
- If this test is done for metabolic disorder, then advise the patient to have a low calcium diet, and stop calcium medications 1 to 3days before the urine collection.
- For patients with renal stones, the formation should have the same routine diet for the last three days before the collection of the urine. Can continue medications.
- This is done to evaluate calcium intake (hypercalcemia).
- This also tells the rate of :
- Absorption of calcium from the GI tract.
- Bone Resorption.
- Renal loss.
- Measurement of calcium level in urine and serum levels are used to diagnose and monitor disorders of calcium metabolism.
- This test is also used in the stone evaluation and follow-up.
- Urine calcium is also advised for the calcium intake or rate of intestinal absorption, bone resorption, and renal loss.
- Calcium is the fifth most common element in the body.
- An average human body contains 1 kg of calcium.
- Calcium exists in three forms in the blood.
- Calcium in the body exists as intracellular and extracellular and both have different functions.
- Blood calcium level is maintained by the parathyroid hormone.
- PTH indirectly increases the absorption of calcium from the gastrointestinal tract by the production of the vit. D.
- PTH increases the serum calcium level by increasing bone resorption and mobilizing Calcium.
- Urine calcium is high in 30% to 80% of cases of primary hyperparathyroidism, but it does not diagnostic.
- Calcium excretion:
- Mostly calcium is lost in the stool.
- The very small amount is excreted in the urine.
- In hypercalcemia, there is increased secretion of calcium in the urine.
- In hypocalcemia, there is decreased secretion of calcium in the urine.
- Urinary calcium excretion is dependant upon the dietary intake of calcium.
- Increased urinary calcium takes place due to:
- Increased intestinal calcium absorption.
- The defect in the renal tubular reabsorption.
- Loss or reabsorption from the bone.
- Or a combination of the above possibilities.
- In primary hyperparathyroid disease, 30 to 80 % of the patient has high urinary calcium.
- Urine calcium does not have much value in the differential diagnosis.
|Infants and child
||up to 6.0 mg/Kg/day
|Ca-free diet||5 to 40||0.13 to 1.0|
|Low to average Ca-diet||50 to 150||1.25 to 3.75|
|Average Ca-diet||100 to 300||2.50 to 7.50|
- The average Calcium diet is 800 mg/day.
- Normal diet = 100 to 300 mg/ 24 hours or 2.50 to 7.50 mmol/day.
- Low calcium diet = 100 to 150 mg /24 hours or 1.25 to 3.75 mmol/day.
- 50 to 250 mg/24 hours.
False raised values are seen in:
- Some of the drugs like calcitonin, vitamins A, K, and C.
- Urine is taken after meals with high calcium intake e.g milk.
- Increased exposure to sunlight.
- Immobilization especially in the children.
False decreased values are seen in:
- Increased ingestion of PO4, HCO3–, and antacid.
- Thiazide diuretics.
- Lithium therapy.
- Alkaline urine.
- Oral contraceptives, and estrogens.
Increased urinary calcium:
- In hyperparathyroidism, 30 to 80% of the cases.
- Paget’s diseases.
- Renal diseases.
- Breast cancer.
- Urinary bladder cancers.
- Multiple Myeloma.
- Bone metastasis (osteolytic).
- Vit.D intoxication.
- Fanconi’s syndrome.
- Idiopathic hypercalciuria.
- Prolonged immobilization.
Decreased urinary calcium:
- Renal osteodystrophy.
- Vit.D deficiency.
- Metastatic carcinoma of the prostate.
- Acute renal failure, nephritis, and nephrosis.
- Malabsorption conditions like :
- Celiac disease.
- Sprue disease.
- Drugs like Thiazide and oral contraceptives leads to decrease level.