Davis's Lab & Diagnostic Tests
Calcium, Blood, Total and Ionized and Calcium, Urine
General
Core Lab Study
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.
| 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 | |||||||||||||||||||||||||||||||||||||||
| Values may vary with instrumentation. | |||||||||||||||||||||||||||||||||||||||||
| 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 |
| 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. | |||||||||||||||||||||||||||||||||||||||||
Critical Findings and Potential Interventions
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
- Less than 3.2 mg/dL (SI: Less than 0.8 mmol/L)
- Greater than 6.2 mg/dL (SI: Greater than 1.6 mmol/L)
Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.
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.
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