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08-2009

08-2009. Serum calcium. Blowin’ in the wind. 1947 “The scatter of the measurements and the degree of unreliability is surprising. The accuracy of the measurements is below any reasonable standard”. Allowable total error for serum-calcium: 7.6% at 1.65 mmol/L; 4.0% at 3.15 mmol/L.

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08-2009

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  1. 08-2009 Serum calcium

  2. Blowin’ in the wind • 1947 • “The scatter of the measurements and the degree of unreliability is surprising. The accuracy of the measurements is below any reasonable standard”. • Allowable total error for serum-calcium: 7.6% at 1.65 mmol/L; 4.0% at 3.15 mmol/L. • Belk, WP, Sunderman WF. A survey of the accuracy of chemical analyses in clinical laboratories. Am J Clin Pathol 1947;17:853–61 (reprinted: Arch Pathol Lab Med 1988;112:320-6). Tin Can 2

  3. Blowin’ in the wind • 1991 • B. Doumas: I am more concerned about calcium. I think the target (ie, PT) is dismal and the performance is equally dismal; a tolerance range of ± 1 mg is atrocious. Do you have any idea why interlaboratory performance for calcium is so bad? • Robert Rej: A major point has to do with the way the manufacturers establish calibration procedures and the reference methods on which they base their procedures. • Clinical Chemistry Forum. Bethesda, Maryland, November 18-19, 1991. Discussion Session I. Clin Chem 1992;38:1218-25. Tin Can 2

  4. Blowin’ in the wind • 1991 • David Bruns: A few months ago, the NIH had a consensus conference on the management of asymptomatic primary hyperparathyroidism. The only sticky point they unexpectedly got hung up on was trying to define primary hyperparathyroidism, the problem there being the measurement of calcium and the variability among laboratories. • Robert Rej: The existence of a number of subpopulations for calcium indicates that the major problem is having each of these methods agree with each other; accuracy is a real problem. • Clinical Chemistry Forum. Bethesda, Maryland, November 18-19, 1991. Discussion Session I. Clin Chem 1992;38:1218-25. Tin Can 2

  5. Blowin’ in the wind • End 90ies • ‘‘Based on analysis of over 89,000 patients receiving serum calcium tests at the Mayo Clinic in 1998–1999, we find that the number of follow-up procedures, and hence healthcare costs, is directly related to initial calcium test values. With approximately 3.55 million patients per year receiving screening serum calcium tests being affected by bias, the potential economic impacts range from $60 million to $199 million per year for analytic biases of 0.1 and 0.5 mg/dL, respectively’’. • Gallagher MP, Mobley LR, Klee GG, Schryver P. RTI planning report 04-1, the impact of calibration error in medical decision making. NIST. U.S. Department of Commerce. Technology Administration, April 2004. Tin Can 2

  6. Blowin’ in the wind • Proficiency testing limits 2009 (“Penalty PT’s”) 10% at 1 – 6 mmol/L 1 mg/dL (= 10% at 10 mg/dL) • Bundesärztekammer. Richtlinie der Bundesärztekammer zur Qualitätssicherung laboratoriumsmedizinischer Untersuchungen. Deutsches Ärzteblatt 2008;105:A341-55. • CLIA limits. wwwn.cdc.gov/clia/regs/subpart_i.aspx 1947 (“Observational PT”) 4% at 3.15 mmol/L Tin Can 2

  7. Blowin’ in the wind • Serum calcium measurement • “Don’t worry, be happy” Tin Can 2

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