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Lab Manual for UCSF Clinical Laboratories

Lab Manual for SFGH

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Item Value
Available Stat? Yes
Test code CA
Performed by? Chemistry
Sendout? no
Price range $
In House Availability Routine: 7 days.
STAT: 24 hours/7 days.
Principle Analysis is based on the reaction of calcium with an indicator dye (o-cresolphthalein complexone) to form a colored complex.
Interpretation INDICATIONS:

1. Routine calcium: (serum and urine): diagnosis and management of bone metabolism and calcium dysregulation disorders; cancer screening.

2. Stat calcium: acute seizure activity, acute altered mental status, tetany, pre/post-dialysis, acute arrhythmia, prolonged or shortened QT interval on cardiogram.


1. Serum increased: hyperparathyroidism, vitamin D intoxication, cancer, acute osteoporosis, Burnett's syndrome, idiopathic in infants, infantile hypophosphatasia, berylliosis, hyperthyroidism, hyperproteinemia (i.e., multiple myeloma, sarcoid, collection conditions [tourniquet], oral contraceptives, Ca++ salts).

2. Serum decreased: hypoparathyroidism, malabsorption, hypoalbuminemia of any etiology, CRF with phosphate retention, acute pancreatitis, insufficient ingestion of calcium, phosphate, or vitamin D, osteomalacia, rickets, starvation, late pregnancy.
Container type gel tube (gold or green top)
Amount to Collect 2 mL
Sample type Blood
Special instructions Fasting sample.

Note: Anticoagulants such as EDTA, oxalate & citrate bind calcium and will lead to spuriously low results. Heparinized tubes (green-top) may be used for stats.
Normal range
Age mg/dL mmol/L
14 days-2 yrs 9.0-11.0 2.25-2.74
2-16 yrs 8.8-10.8 2.20-2.69
> 16 yrs 8.6-10.5 2.15-2.62

All values less than 6.5 mg/dL (< 1.62 mmol/L) or greater than 13.5 mg/dL (> 3.37 mmol/L) are considered Critical Values and are called to the physician or patient care unit immediately.
(Ionized fraction varies with serum protein concentration, and especially the albumin content of serum).
Synonyms Metabolic Basic Panel (METB): NA, K, CL, CO2, CREA, BUN, GLUC, CA;
Stability Serum calcium is stable at 4°C for 2-3 days; at -20°C for 6 months.
Interferences Many drugs can increase or decrease serum and urine calcium. If you have any question, please contact the Laboratory Medicine Resident in Clinical Chemistry (x65527, or pager (415) 443-2311).

1. Decrease: fluoride, anticoagulants, glucose infusion, gadolinium dye.

2. Increase: bed rest, diurnal variation, tourniquet.

a See also: Young, D.S. (Reference #2.)
Additional information
References 1. Gitelman, H.J.: An improved automated procedure for the determination of calcium in biochemical specimen. Anal Biochem 18:521-531, 1967.

2. Young DS. Effects of Drugs on Clinical Laboratory Tests ed. 4. Washington D.C.: AACC Press; 1995.

3. Bayer(TM) Clinical Methods Calcium (39) B01-4145-01 Advia 1650 Operator's Guide. PN 073-5001-09. Last accessed June 2003. Siemens Medical Solutions Diagnostics, Malvern, PA.

4. Kang, HP; Scott, MG; Joe, BN; Narra V; Heiken, J; Parvin, CA. Model for predicting the impact of gadolinium on plasma calcium measured by the o-cresolphthalein method. Clin Chem, 2004; 50:741-746.

5. Brown, JJ; Hynes, MR; Wible, JH. Measurement of serum calcium concentration after administration of four gadolinium-based contrast agents to human volunteers. Am J Roentgenol, 2007; 189:1539-1544.

6. Gandhi, MJ; Narra, VR; Brown, JJ; Guo, A; Scott, G. Impact of falsely decreased calcium values due to gadolinium interference. Clin Chem, 2007; 53:A179.
Last Updated 6/18/2011 8:28:38 AM
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