Newcastle Laboratories

Calcium (total and adjusted), serum

Clinical Background:

Blood calcium levels are tightly regulated within a narrow range and circulates in three main forms:• Ionised calcium (physiologically active) at ~47%
• Albumin bound calcium at ~46%
• Complexed (w...

Blood calcium levels are tightly regulated within a narrow range and circulates in three main forms:• Ionised calcium (physiologically active) at ~47%
• Albumin bound calcium at ~46%
• Complexed (with citrate, phosphate etc) at ~7%

As calcium is ~46% albumin bound an adjusted calcium value is also calculated and reported to make allowance for albumin concentration in the sample The formula used for the calculation is:

Adjusted serum calcium = Total serum calcium + ((47.2-serum albumin) x 0.0127)

The references ranges for adjusted and total serum calcium are the same.
Because a significant portion of calcium is bound to albumin, any alteration in the level of albumin will affect the level of calcium is measured.This calculation is an approximation and is invalid at extreme concentrations of albumin, typically <20g/L. Direct measurement of ionised calcium is advisable in these cases.

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Test Details

  • Discipline:

    Biochemistry

    Biochemistry

  • Specimen Container Adult:

    Serum (SST or plain tube)

    Serum (SST or plain tube)

  • Specimen Container Paediatric:

    Serum (SST or plain tube)

    Serum (SST or plain tube)

  • Minimum Volume Adult:

    1 mL blood

    1 mL blood

  • Minimum Volume Paediatric:

    0.5 mL blood

    0.5 mL blood

  • Sample Stability:

    Unseparated sample: 2 days

    Separated sample:

    - 7 days at 15-25C

    - 3 weeks at 4ºC

    - 8 months at -20C 

    Unseparated sample: 2 days

    Separated sample:

    - 7 days at 15-25C

    - 3 weeks at 4ºC

    - 8 months at -20C 

  • Reference Ranges:

    Age up to 4 weeks: 2.0 – 2.7 mmol/L

    Age 4 weeks to 16 years: 2.2 – 2.7 mmol/L

    Age 16 years and over: 2.2 – 2.6 mmol/L

    Age up to 4 weeks: 2.0 – 2.7 mmol/L

    Age 4 weeks to 16 years: 2.2 – 2.7 mmol/L

    Age 16 years and over: 2.2 – 2.6 mmol/L

  • Factors Affecting Result:

    EDTA, oxalate and citrated samples are unsuitable
    Blood for measurement of total calcium should ideally be drawn from a vein in which the blood is free‐flowing (that is, without a tourniquet)

    EDTA, oxalate and citrated samples are unsuitable
    Blood for measurement of total calcium should ideally be drawn from a vein in which the blood is free‐flowing (that is, without a tourniquet)

  • Other Info:

    lithium heparin plasma sample also acceptable

    lithium heparin plasma sample also acceptable

  • Routine Contact Name:

    Duty Biochemist

  • Routine Telephone:

    Freeman: 0191 244 8889
    RVI: 0191 282 9719

    Freeman: 0191 244 8889
    RVI: 0191 282 9719

  • Routine Email:

Availability:

24/7, analysed at RVI and Freeman

Turn Around:

Urgent: within 1 hour,
Non urgent: within 4 hours

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