Abstract: TH-PO1110
Correcting Serum Potassium ([K]) in Critical Care
Session Information
- Fluid, Electrolyte, Acid-Base Disorders
November 02, 2017 | Location: Hall H, Morial Convention Center
Abstract Time: 10:00 AM - 10:00 AM
Category: Fluid, Electrolytes, and Acid-Base
- 704 Fluid, Electrolyte, Acid-Base Disorders
Authors
- Goldwasser, Philip, VA NY Harbor Healthcare System, Brooklyn, New York, United States
- Roche-Recinos, Andrea, SUNY Downstate, Brooklyn, New York, United States
- Barth, Robert H., VA NY Harbor Healthcare System, Brooklyn, New York, United States
Background
High platelet counts (PLT) positively bias serum [K] in chemistry panels (CK). Because the CK assay uses indirect potentiometry, it should also be positively biased by low total protein (TP), common in critical care, but this is unproved. Neither bias should affect [K] measured in gas panels (GK) in whole blood anticoagulated with electrolyte-balanced heparin. Since even a subtle bias in CK might be important at a decision limit, we sought to derive a practical correction for commonly seen values of PLT on CK - GK (ΔK), as well as to confirm TP bias.
Methods
In our critical care database (Clin Biochem 2017), we found 710 patients who had CK, GK, TP, and PLT obtained < 20 min. apart (median: 4 min). We excluded 17 cases with PLT ≥500 (units:109/L), as such values (i) are already known to bias CK, and, (ii) being extreme, might skew the estimated effect of more usual PLT values. The independent effects of PLT and TP upon ΔK were estimated with multivariate methods.
Results
Mean values (±SE) were: PLT, 209±3.5 [range: 4-497]; TP, 6.5 ±0.04 g/dL [2.1-10.1]; ΔK, 0.27± 0.01 mEq/L [-1.8 to +2.5; 21% of values ≥ 0.5]. PLT correlated with both ΔK (r=0.13 p<10-3) and TP (r= 0.19 p<10-6). TP and ΔK didn’t correlate (r=-0.06 p=0.11), possibly the result of confounding by PLT. No nonlinear effects of PLT category (TABLE) on ΔK were detected by ANOVA with polynomial contrast. By multiple linear regression, ΔK rose 0.053±0.014 mEq/L with each PLT rise of 100 (p=10-4) and by 0.026±0.011 (p=0.02) with each 1 g/dL fall in TP (model adj. R2=.024).
Conclusion
The accuracy of CK can be improved simply with a 0.05 mEq/L reduction per 100 PLT rise. The effect of TP on CK is minor, but, proportionally, the same as its effect on serum [Na]. Much of the variation in CK relative to GK is unexplained.
Mean Values by PLT Category
| PLT Category (mean) | N | CK | GK | ΔK (% cases ≧ 0.5) | TP |
| 0-99 (65) | 65 | 4.24 | 4.00 | .238 ± .031 (17%) | 5.9 |
| 100-199 (156) | 284 | 4.30 | 4.05 | .245 ± .019 (19%) | 6.4 |
| 200-299 (242) | 232 | 4.44 | 4.16 | .278 ± .021 (21%) | 6.7 |
| 300-399 (337) | 79 | 4.49 | 4.14 | .346 ± .045 (28%) | 6.8 |
| 400-499 (443) | 29 | 4.53 | 4.15 | .383 ± .091 (38%) | 6.4 |
Funding
- Veterans Affairs Support