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. 2016 Aug;37(3):113–119.

Table 1.

Formulae available for calculated osmolality (units for all analytes are mmol/L).*

Number Formula
1 1.75(Na) + Glu + 0.5(Urea) + 10.1
2 2.63(Na) − 65.4
3 1.86(Na) + Glu + 0.5(Urea)
4 2(Na + K) + Glu + 0.5(Urea)
5 1.85(Na) + 1.84(K) + 1.15(iCa) + 1.17(Mg) + Glu + 0.5(Urea)
6 2(Na)
7 2(Na) + Glu + 0.5(Urea)
8 2(Na) + 7
9 2(Na) + 10
10 2(Na) + Glu
11 2.1(Na)
12 2(Na) + Glu + 0.93 × 0.5(Urea)
13 0.985[2(Na + K) + Glu + 0.5(Urea)]
14 1.86(Na) + Glu + 0.5(Urea) + 5
15 2(Na) + 0.9(Glu) + 0.93(Urea) × 0.5
16 2(Na) + 0.5(Urea)
17 [1.86(Na) + Glu + 0.5(Urea)] / 0.93
18 1.9(Na + K) + Glu + 0.5(Urea)
19 1.8(Na + K + iCa) + Glu + 0.47 × 0.5(Urea)
20 1.85(Na) + Glu + 0.5(Urea) + 8.55
21 1.86(Na) + Glu + 0.5(Urea) + 9
22 1.86(Na) + Glu + Urea + 9
23 2(Na + K) + Glu + 0.93 × 0.5(Urea)
24 1.89(Na) + 1.38(K) + 1.08(Glu) + 1.03(Urea) + 7.47
25 1.86(Na + K) + Glu + Urea + 10
26 2(Na) + 0.9(Glu) + 0.93 × 0.5(Urea) + 8
27 0.985[1.86(Na) + 1.03(Glu) + 1.28 × 0.5(Urea)]
28 1.36(Na) + 1.6(Glu) + 0.45(Urea) + 91.75
29 0.985[2(Na) + Glu + Urea + 35.2)]
30 1.897(Na) + Glu + 0.5(Urea) + 13.5
31 1.9(Na + K) + Glu + 0.5(Urea) + 5
32 1.86(Na + K) + Glu + Urea
33 2(Na) + 1.15(Glu) + Urea
34 1.86(Na + K) + 1.15(Glu) + Urea + 14
35 1.09 × 1.86(Na) + Glu + Urea
36 0.985(Na + K + Cl + HCO3+ Lactate + Glu + Urea + 6.5)
37 2(Na) + Glu + Urea
*

Formulae 1–36 adapted from Fazekas et al10; formula 37 from Smithline and Gardner23

Abbreviations: Na, sodium; Glu, glucose; K, potassium; Mg, magnesium; iCa, ionised calcium; Cl, chloride