Alarming (or Near-Critical) Results Are Highlighted to Alleviate Adverse Outcome

• Elie Benmouyal
Medicine
Part of the following topical collections:
1. Topical Collection on Medicine

Abstract

Near-critical levels of laboratory results are derived by using simple calculations, which take critical levels into account. These calculations provide a framework whereby the guesswork is removed when the need arises to identify and act upon these near-critical results.

Keywords

Alarming laboratory results Calculating near critical levels Appended comment to reports

Introduction

A coroner investigation followed the death of a very sick ambulatory patient who, a few days before he passed away, had blood glucose of 22.3 mmol/L. In his final report, the coroner, a trained physician, recommended in his report [1] that “clinical laboratories should provide a written warning that automatically prints under certain alarming results, although below a defined critical level.”

The health agency of the territory advised all clinical laboratories to abide by that recommendation. To implement it, the question was to choose alarming levels; the present communication proposes two avenues of calculations.

Calculations

First Approach

Starting with the equation [2] for a significant change between two values, namely the critical level and the alarming level:
$$\mathrm{RCV}={2}^{1/2}\times \mathrm{Z}\times {\left[{\mathrm{CVa}}^2+{\mathrm{CVi}}^2\right)}^{1/2}$$
(1)
where the relative change is a function of the analytical precision CVa, the intra-individual variation CVi, and Z which, at the 95% level of significance, equals 1.96.
Defining alarming high as AH, critical high as CH, alarming low as AL, critical low as CL, the upper limit of the reference range as UL, and the lower limit of the reference range as LL, then solving Eq. (1) gives RCV = 0.30 when CVa is 0.05 and CVi is 0.10; in this example, the alarming high AH is so derived:
$$\left(\mathrm{AH}\right)+\left(\mathrm{AH}\ \mathrm{x}\ 0.30\right)=\mathrm{CH};\mathrm{and}\ \mathrm{AH}=\mathrm{CH}/1.3$$
Similarly, the alarming low AL is off by a factor of 0.30 from the critical low CL:
$$\left(\mathrm{AL}\right)+\left(\mathrm{AL}\ \mathrm{x}\ 0.30\right)=\mathrm{CL};\mathrm{and}\ \mathrm{AL}=\mathrm{CL}\ \mathrm{x}\ 1.3$$

Second Approach

This takes into account both the laboratory-defined value of the upper limit of the reference range UL, and the chosen value of the critical high CH (or the defined value of the lower limit of the reference range LL, and the chosen value of the critical low CL).

Empirically, it is practical and simple to divide by 4 the difference between CH and UL, and one quarter of that difference is subtracted from CH to obtain AH (or to divide by 4 the difference between LL and CL, and one quarter of that difference is added to CL to obtain AL), as:
$$\mathrm{AH}=\mathrm{CH}-\left[\left(\mathrm{CH}-\mathrm{UL}\right)/4\right]$$
(2)
$$\mathrm{AL}=\mathrm{LL}-3\ \mathrm{x}\ \left[\left(\mathrm{LL}-\mathrm{CL}\right)/4\right]$$
(3)

Results and Discussion

Table 1 shows examples of such calculations.
Table 1

Examples of calculation of alarming high AH by applying Eqs. (1) and (2), and of alarming low AL by applying Eqs. (1) and (3); CVi are taken from reference [3]

 Calculation of alarming high AH Test CVa CVi RCV UL CH AH (Eq. 1) AH (Eq. 2) ALT 1.6 18 0.5 40 400 266 310 Glucose 3.4 6.1 0.19 6.0 24 20.2 19.5 Sodium 1.24 0.7 0.07 144 160 149 156 Total bilirubin 2.45 23.8 0.66 34 260 157 204 Calculation of alarming low AL Test CVa CVi RCV LL CL AL (Eq. 1) AL (Eq. 3) Albumin 1.7 3.1 0.1 40 20 22 25 Calcium 1.9 2.2 0.08 2.12 1.55 1.67 1.69 Sodium 1.24 0.7 0.07 134 120 128 124 Potassium 2.65 4.8 0.15 3.5 2.6 3.0 2.8

Albumin in g/L, AST in U/L, calcium, glucose, sodium, and potassium in mmol/L, and total bilirubin in μmol/L

The alarming high AH range for glucose is, depending of the approach, either between 20.2 and 24.0, or between 19.5 and 24.0. Similarly, the alarming low AL range for sodium is between 120 and 128, or between 120 and 124.

The coroner’s recommendation has been in place in our laboratory for a few years, and the physicians welcomed it with no single objection. For chemistries for which critical results are reported, alarming levels are set correspondingly.

Persons other than the busy treating physician may access laboratory results, and they may not appreciate the implications of a simply flagged near-critical result; so an appended comment to that result provides the insurance it will be considered accordingly.

Alarming results can easily be spotted on a report with a comment automatically printed under the AH (or the AL) result, in addition to being flagged as “high” or “low.”

The printed comment may be worded as “this result is at an alarming level; a quick intervention of the attending physician is required.”

The primary purpose of this presentation remains the proposed calculations of the near-critical results, and it is the responsibility of each institution to choose the most appropriate method to communicate them effectively. The one adopted, namely an appended comment to the near-critical result, could ideally in the near future be coupled to an electronic message directly sent to the caregiver. Implementing the recommendation would for sure correspond to a preventive measure, in line with the norms of accreditation bodies such as ISO-15189.

An implied evident benefit in reporting near-critical results is to warn against a possible impending critical result, for the only purpose of preventing further morbidity. The present approach is easily applicable through the lab information system, and there is no risk associated to the obvious benefit of implementing it.

The results of the two approaches are equivalent, the slight differences in the values resulting from the two calculations being not statistically significant; this is verified for the 21 tests for which critical highs or critical lows are effective in our setting. Is one calculation preferred over the other is a matter of local preference: being at ease to perform one calculation rather than the other, choosing the alarming limits which preferably generate the least laboratory interventions. If alarming highs are to be defined for drugs, Eqs. (2) and (3) are obviously used.

In conclusion, the procedure of reporting near-critical laboratory results of ailing patients follows the recommendation of the coroner, and it is most helpful in alerting the caregiver of a potential deterioration of the patients’ health condition. Two simple ways of calculating the limits of near-critical levels are proposed.

References

1. 1.
Office of the coroner. Government of Quebec, QC, Canada. 2013; Case A-316581.Google Scholar
2. 2.
Fraser CG, Harris CG. Generation and application of data on biological variation in clinical chemistry. Crit Rev Clin Lab Sci. 1989;27:409–37.
3. 3.
Ricos C, Alvarez V, Cava F, Garcia-Lario JV, Hernandez A, Jimenez CV, et al. Current databases on biologic variation: pros, cons and progress. Scand J Clin Lab Invest. 1999;59:491–500.