Albumin adjustment of total calcium not justified
In secondary hypoparathyroidism, the serum PTH concentration is low and the The relationship between total serum calcium and albumin is. Formula: Corrected calcium = serum calcium + * (4 - serum albumin). Normal values for total serum calcium during pregnancy. All calculations must be. Increase the active ionised calcium. Relation of calcium to albumin. Ionised Ca is inversely related to serum albumin; Total serum Ca is directly.
It is ionized calcium that is physiologically active and under homeostatic control; however, total calcium is more conveniently measured. Formulae for correction of calcium to account for albumin binding have not been validated in a dialysis setting. We measured ionized calcium simultaneously with total calcium t[Ca]albumin, total protein and pH before dialysis in 50 stable outpatients and convalescent inpatients.
Results are expressed as intraclass correlation coefficients ICC: None of the published formulae greatly improved the test characteristics beyond simply using the total calcium.
A correction formula in widespread use Paynequoted in reference texts, agreed less well with ionized calcium than did the unadjusted measured calcium. Correction formulae should be abandoned in favour of the use of uncorrected calcium.
In cases of doubt, ionized calcium should be directly measured. The methodologies used in the development of these formulae varied: The literature on correction of calcium is, therefore, deficient in evidence supporting the use of formulae for the correction of calcium in any population.
Calcium in serum exists in three fractions: It is this last fraction which has biological activity and is under homeostatic control.
The equilibrium between the fractions is dependent on a number of variables, most importantly, the concentrations of serum proteins and the pH. While the measurement of total calcium, albumin and total protein is available in standard laboratories, measurement of ionized calcium remains more difficult and is generally performed only in reference laboratories. In addition, great care must be taken with the method of venepuncture and subsequent sample handling [ 4 ].
Patient posture and the use of a tourniquet, through changes in pH and total protein concentration, alter the concentration of ionized calcium. Samples should be drawn anaerobically to minimize loss of carbon dioxidetransported on ice and processed within hours to minimize lactate generation.
Heparin contamination must be avoided as it interferes with the assay.
Corrected Calcium Calculator
These stringent conditions make accurate measurement of ionized calcium problematic in many settings. Previous studies have used Pearson correlation coefficients as the metric of goodness of fit between measured and predicted values. Under this estimate, predictions which are systematically biased will correlate as highly as those which are not, provided the closeness of the data to a linear relationship is similar.
For estimating clinical utility, a measure of agreement an intraclass correlation coefficient is more appropriate than a measure of correlation. Rather than being a measure of closeness of fit to an unspecified linear relationship, agreement describes how well the data correspond to the line of identity i.
Relationship of serum total calcium to albumin and total protein in dogs.
Subjects and methods Patients Consecutive haemodialysis patients who were either outpatients dialysing in a hospital setting, or stable haemodialysis inpatients undergoing rehabilitation were studied. Investigators retrieved calcium results data for all instances at their hospital during an 8-year period to when ionized calcium, total calcium and albumin were measured on the same sample.
In total, this generated 16, data sets for statistical analysis. They employed six different formulae to calculate six different corrected total calcium values for each of the 16, retrieved total calcium results. Using the ionized calcium results as reference, they compared agreement between ionized calcium and uncorrected total calcium results with agreement between ionized calcium and each of the six corrected total calcium results.
The statistical method of comparison was intraclass correlation coefficients ICCwhich generates values from 0 no agreement to 1 perfect agreement. Equal or worse level of agreement was evident when ionized calcium result was compared with corrected total calcium; depending on the correction formula used, ICC values ranged from 0.
A second method of analyzing the data was also employed. Investigators categorized all ionized calcium results to one of three groups: By contrast, corrected total calcium results predicted correct calcium status in lower percentage of cases.
In summary, the authors of this study find no evidence that albumin correction of calcium results adds useful clinical information; they suggest that the practice should be abandoned.