355:. Even though these values are presented in different units, when there is a small amount of solute compared to total volume of solution, the absolute values of osmolality vs. osmolarity are very close. Often, this results in confusion as to which units are meant. For practical purposes, the units are considered interchangeable. The resulting "osmolar gap" can be thought of as either osmolar or osmolal, since both units have been used in its derivation.
346:
is the difference between the measured osmolality and the calculated osmolarity. The difference in units is attributed to the difference in the way that blood solutes are measured in the laboratory versus the way they are calculated. The laboratory value measures the freezing point depression,
99:
used for osmolality) excludes the weight of any solutes, whereas the total solution volume (used for osmolarity) includes solute content. Otherwise, one litre of plasma would be equivalent to one kilogram of plasma, and plasma osmolarity and plasma osmolality would be equal. However, at low
200:
Plasma osmolarity of some reptiles, especial those from a freshwater aquatic environment, may be lower than that of mammals (e.g. < 260 mOsm/L) during favourable conditions. Consequently, solutions osmotically balanced for mammals (e.g., 0.9% normal saline) are likely to be mildly
237:(ICF). Therefore, plasma osmolality is a guide to intracellular osmolality. This is important, as it shows that changes in ECF osmolality have a great effect on ICF osmolality — changes that can cause problems with normal cell functioning and volume. If the ECF were to become too
175:. In practice, there is almost negligible difference between the absolute values of the different measurements. For this reason, both terms are often used interchangeably, even though they refer to different units of measurement.
212:
Deep-sea fish have adapted to the extreme hydrostatic pressures of depth through a number of factors, including increasing osmolality, with one of the deepest known fish in the world, the hadal snailfish
361:
Clinically, the osmolar gap is used to detect the presence of an osmotically active particle that is not normally found in plasma, usually a toxic alcohol such as ethanol, methanol or isopropyl alcohol.
754:
271:
217:
having a recorded muscle osmolality of 991 ± 22 mOsmol/kg, almost four times the osmolality of mammals and three times that of shallow water fish species (typically 350 mOsmol/kg).
91:
Osmolarity is affected by changes in water content, as well as temperature and pressure. In contrast, osmolality is independent of temperature and pressure. For a given solution,
677:
Purssell RA, Pudek M, Brubacher J, Abu-Laban RB (December 2001). "Derivation and validation of a formula to calculate the contribution of ethanol to the osmolal gap".
274:
occurs when excessive release of antidiuretic hormone results in inappropriately elevated urine osmolality (>100 mOsmol/L) relative to the blood plasma, leading to
268:, and less concentrated blood plasma. A low serum osmolality will suppress the release of ADH, resulting in decreased water reabsorption and more concentrated plasma.
747:
297:
In medical lab reports, this quantity often appears as "Osmo, Calc" or "Osmo (Calc)." According to the international SI unit use the following equation :
100:
concentrations (below about 500 mM), the mass of the solute is negligible compared to the mass of the solvent, and osmolarity and osmolality are very similar.
740:
712:
47:
are measures that are technically different, but functionally the same for normal use. Whereas osmolality (with an "l") is defined as the number of
249:). Many poisons, medications and diseases affect the balance between the ICF and ECF, affecting individual cells and homeostasis as a whole.
326:
Based on the molecular weight of ethanol the divisor should be 4.6 but empiric data shows that ethanol does not behave as an ideal osmole.
303:
As Na+ is the major extracellular cation, the sum of osmolarity of all other anions can be assumed to be equal to natremia, hence x2 ≈ +
1052:
189:
358:
Measured osmolality is abbreviated "MO", calculated osmolarity is abbreviated "CO", and the osmolality gap is abbreviated "OG".
566:
Hannon MJ, Thompson CJ (June 2010). "The syndrome of inappropriate antidiuretic hormone: prevalence, causes and consequences".
1253:
1009:
945:
907:
1286:
837:
260:
and decreases with overhydration. In normal people, increased osmolality in the blood will stimulate secretion of
1114:
209:
species allow major elevations of plasma osmolarity (e.g. > 400 mOsm/L) that could be fatal to some mammals.
127:
34:
987:
982:
850:
815:
618:
1248:
1102:
940:
902:
716:
630:
96:
400:
1042:
1019:
1004:
935:
371:
67:(osmol/L or Osm/L). As such, larger numbers indicate a greater concentration of solutes in the plasma.
1311:
1240:
1097:
1085:
1062:
917:
785:
491:
283:
261:
64:
1078:
1073:
970:
810:
635:
279:
234:
230:
795:
656:
599:
59:(osmol/kg or Osm/kg), osmolarity (with an "r") is defined as the number of osmoles of solute per
1180:
1159:
827:
694:
648:
591:
583:
527:
509:
440:
37:. There are several methods for arriving at this quantity through measurement or calculation.
1270:
927:
686:
640:
575:
517:
499:
430:
376:
1263:
1258:
617:
Bhalla A, Sankaralingam S, Dundas R, Swaminathan R, Wolfe CD, Rudd AG (September 2000).
495:
1171:
1027:
800:
790:
522:
480:"Marine fish may be biochemically constrained from inhabiting the deepest ocean depths"
479:
134:
80:
241:, water would readily fill surrounding cells, increasing their volume and potentially
1305:
1214:
1193:
1107:
1032:
965:
381:
226:
48:
732:
1219:
1188:
1091:
992:
780:
603:
275:
660:
435:
1037:
997:
977:
912:
874:
865:
860:
855:
772:
257:
484:
Proceedings of the
National Academy of Sciences of the United States of America
306:
To calculate plasma osmolality use the following equation (typical in the US):
957:
897:
884:
805:
764:
619:"Influence of raised plasma osmolality on clinical outcome after acute stroke"
352:
348:
206:
172:
168:
92:
44:
644:
587:
545:
513:
418:
1129:
1124:
1119:
1047:
845:
690:
504:
342:
335:
246:
138:
130:
76:
698:
652:
595:
531:
444:
264:(ADH). This will result in increased water reabsorption, more concentrated
458:
1209:
1141:
892:
238:
202:
52:
40:
579:
478:
Yancey PH, Gerringer ME, Drazen JC, Rowden AA, Jamieson A (2014-03-25).
95:
is slightly less than osmolality, because the total solvent weight (the
1149:
315:
56:
155:
derived from lab data that were measured in solutions (Na, Glu, Urea)
1154:
318:, the ethanol level should be included in the calculated osmolarity:
192:
of osmolality in plasma is about 275-299 milli-osmoles per kilogram.
171:, whereas laboratory measurements will provide readings in units of
265:
253:
242:
60:
75:
Osmolality can be measured on an analytical instrument called an
229:
in general are freely permeable to water, the osmolality of the
205:
for such animals. Many arid species of reptiles and hibernating
736:
300:
Calculated osmolarity = 2 Na + Glucose + Urea (all in mmol/L)
278:. This ADH secretion may occur in excessive amounts from the
419:"Osmolality and osmolarity: narrowing the terminology gap"
167:
Therefore, bedside calculations are actually in units of
1279:
1239:
1232:
1202:
1179:
1170:
1140:
1061:
1018:
956:
926:
883:
836:
771:
310:= 2 + /18 + /2.8 where and are measured in mg/dL.
289:Elevation may be associated with stroke mortality.
103:Technically, the terms can be compared as follows:
23:
713:"Osmolality Gap - Calculation and Interpretation"
351:while the calculated value is given in units of
672:
670:
748:
8:
233:(ECF) is approximately equal to that of the
1236:
1176:
755:
741:
733:
79:. It works on the method of depression of
634:
521:
503:
434:
105:
392:
272:Syndrome of inappropriate ADH secretion
20:
7:
1053:Glycogen phosphorylase isoenzyme BB
282:, or from ectopic sources such as
14:
568:European Journal of Endocrinology
284:small-cell carcinoma of the lung
459:"Case 422 —Neuropathology Case"
382:Serum Osmolarity vs. Osmolality
1:
1010:Comprehensive metabolic panel
436:10.1592/phco.23.10.1085.32751
546:"Serum and Urine Osmolality"
417:Erstad BL (September 2003).
314:If the patient has ingested
87:Osmolality versus osmolarity
946:Thyroid-stimulating hormone
908:Total iron-binding capacity
1328:
1287:Elevated alpha-fetoprotein
333:
293:Calculated osmolarity (CO)
215:Notoliparis kermadecensis)
280:posterior pituitary gland
128:freezing point depression
35:electrolyte–water balance
645:10.1161/01.str.31.9.2043
71:Measured osmolality (MO)
816:BUN-to-creatinine ratio
691:10.1067/mem.2001.119455
505:10.1073/pnas.1322003111
322:= 2 + /18 + /2.8 + /3.7
1249:Elevated transaminases
941:Thyroid function tests
903:Transferrin saturation
763:Clinical biochemistry
407:, accessed 2012-01-11.
123:clinical laboratories
1043:Lactate dehydrogenase
1005:Basic metabolic panel
936:ACTH stimulation test
372:Osmotic concentration
152:bedside calculations
1063:Liver function tests
918:Transferrin receptor
262:antidiuretic hormone
51:(Osm) of solute per
33:measures the body's
1079:Serum total protein
1074:Human serum albumin
580:10.1530/eje-09-1063
496:2014PNAS..111.4461Y
235:intracellular fluid
231:extracellular fluid
851:Arterial blood gas
574:(Suppl1): S5–S12.
221:Clinical relevance
1299:
1298:
1295:
1294:
1228:
1227:
1181:Blood sugar level
1160:Pancreatic lipase
998:Total cholesterol
828:Serum osmolal gap
823:Plasma osmolality
490:(12): 4461–4465.
165:
164:
115:Appropriate term
31:Plasma osmolality
28:
27:
24:Plasma osmolality
1319:
1271:Hyperproteinemia
1237:
1177:
757:
750:
743:
734:
728:
727:
725:
724:
715:. Archived from
709:
703:
702:
674:
665:
664:
638:
614:
608:
607:
563:
557:
556:
554:
553:
542:
536:
535:
525:
507:
475:
469:
468:
466:
465:
455:
449:
448:
438:
414:
408:
405:Lab Tests Online
397:
377:Urine osmolality
347:properly called
330:Osmolar gap (OG)
106:
21:
1327:
1326:
1322:
1321:
1320:
1318:
1317:
1316:
1302:
1301:
1300:
1291:
1275:
1264:Hypoalbuminemia
1259:Hypoproteinemia
1224:
1198:
1172:Small molecules
1166:
1136:
1057:
1014:
952:
922:
879:
869:
832:
767:
761:
731:
722:
720:
711:
710:
706:
676:
675:
668:
616:
615:
611:
565:
564:
560:
551:
549:
544:
543:
539:
477:
476:
472:
463:
461:
457:
456:
452:
423:Pharmacotherapy
416:
415:
411:
398:
394:
390:
368:
338:
332:
295:
256:increases with
223:
198:
190:reference range
186:
181:
89:
73:
17:
12:
11:
5:
1325:
1323:
1315:
1314:
1304:
1303:
1297:
1296:
1293:
1292:
1290:
1289:
1283:
1281:
1277:
1276:
1274:
1273:
1268:
1267:
1266:
1256:
1251:
1245:
1243:
1234:
1230:
1229:
1226:
1225:
1223:
1222:
1217:
1212:
1206:
1204:
1200:
1199:
1197:
1196:
1191:
1185:
1183:
1174:
1168:
1167:
1165:
1164:
1163:
1162:
1152:
1146:
1144:
1138:
1137:
1135:
1134:
1133:
1132:
1127:
1117:
1112:
1111:
1110:
1105:
1100:
1088:
1083:
1082:
1081:
1076:
1067:
1065:
1059:
1058:
1056:
1055:
1050:
1045:
1040:
1035:
1030:
1028:Cardiac marker
1024:
1022:
1020:Cardiovascular
1016:
1015:
1013:
1012:
1007:
1002:
1001:
1000:
995:
990:
985:
975:
974:
973:
971:Hemoglobin A1c
962:
960:
954:
953:
951:
950:
949:
948:
938:
932:
930:
924:
923:
921:
920:
915:
910:
905:
900:
895:
889:
887:
881:
880:
878:
877:
872:
867:
863:
858:
853:
848:
842:
840:
834:
833:
831:
830:
825:
820:
819:
818:
813:
808:
801:Renal function
798:
793:
788:
783:
777:
775:
769:
768:
762:
760:
759:
752:
745:
737:
730:
729:
704:
666:
636:10.1.1.510.254
609:
558:
537:
470:
450:
409:
391:
389:
386:
385:
384:
379:
374:
367:
364:
334:Main article:
331:
328:
324:
323:
312:
311:
294:
291:
252:Osmolality of
227:cell membranes
222:
219:
197:
194:
185:
182:
180:
177:
163:
162:
159:
156:
153:
149:
148:
145:
142:
135:vapor pressure
124:
120:
119:
116:
113:
110:
88:
85:
81:freezing point
72:
69:
26:
25:
15:
13:
10:
9:
6:
4:
3:
2:
1324:
1313:
1310:
1309:
1307:
1288:
1285:
1284:
1282:
1278:
1272:
1269:
1265:
1262:
1261:
1260:
1257:
1255:
1252:
1250:
1247:
1246:
1244:
1242:
1238:
1235:
1231:
1221:
1218:
1216:
1215:Hyperuricemia
1213:
1211:
1208:
1207:
1205:
1201:
1195:
1194:Hyperglycemia
1192:
1190:
1187:
1186:
1184:
1182:
1178:
1175:
1173:
1169:
1161:
1158:
1157:
1156:
1153:
1151:
1148:
1147:
1145:
1143:
1139:
1131:
1128:
1126:
1123:
1122:
1121:
1118:
1116:
1113:
1109:
1108:AST/ALT ratio
1106:
1104:
1101:
1099:
1096:
1095:
1094:
1093:
1092:transaminases
1089:
1087:
1084:
1080:
1077:
1075:
1072:
1071:
1069:
1068:
1066:
1064:
1060:
1054:
1051:
1049:
1046:
1044:
1041:
1039:
1036:
1034:
1033:Troponin test
1031:
1029:
1026:
1025:
1023:
1021:
1017:
1011:
1008:
1006:
1003:
999:
996:
994:
993:Triglycerides
991:
989:
986:
984:
981:
980:
979:
976:
972:
969:
968:
967:
966:Blood glucose
964:
963:
961:
959:
955:
947:
944:
943:
942:
939:
937:
934:
933:
931:
929:
925:
919:
916:
914:
911:
909:
906:
904:
901:
899:
896:
894:
891:
890:
888:
886:
882:
876:
873:
871:
864:
862:
859:
857:
854:
852:
849:
847:
844:
843:
841:
839:
835:
829:
826:
824:
821:
817:
814:
812:
809:
807:
804:
803:
802:
799:
797:
794:
792:
789:
787:
784:
782:
779:
778:
776:
774:
770:
766:
758:
753:
751:
746:
744:
739:
738:
735:
719:on 2009-08-04
718:
714:
708:
705:
700:
696:
692:
688:
684:
680:
679:Ann Emerg Med
673:
671:
667:
662:
658:
654:
650:
646:
642:
637:
632:
629:(9): 2043–8.
628:
624:
620:
613:
610:
605:
601:
597:
593:
589:
585:
581:
577:
573:
569:
562:
559:
547:
541:
538:
533:
529:
524:
519:
515:
511:
506:
501:
497:
493:
489:
485:
481:
474:
471:
460:
454:
451:
446:
442:
437:
432:
429:(9): 1085–6.
428:
424:
420:
413:
410:
406:
402:
396:
393:
387:
383:
380:
378:
375:
373:
370:
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359:
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329:
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320:
319:
317:
309:
308:
307:
304:
301:
298:
292:
290:
287:
285:
281:
277:
276:hyponatraemia
273:
269:
267:
263:
259:
255:
250:
248:
244:
240:
236:
232:
228:
220:
218:
216:
210:
208:
204:
195:
193:
191:
188:Normal human
183:
178:
176:
174:
170:
160:
157:
154:
151:
150:
146:
143:
140:
136:
132:
129:
125:
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117:
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111:
108:
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101:
98:
94:
86:
84:
82:
78:
70:
68:
66:
62:
58:
54:
50:
46:
42:
38:
36:
32:
22:
19:
1254:Elevated ALP
1220:Hypouricemia
1189:Hypoglycemia
1125:Unconjugated
1090:
822:
773:Electrolytes
721:. Retrieved
717:the original
707:
685:(6): 653–9.
682:
678:
626:
622:
612:
571:
567:
561:
550:. Retrieved
540:
487:
483:
473:
462:. Retrieved
453:
426:
422:
412:
404:
395:
360:
357:
341:
339:
325:
313:
305:
302:
299:
296:
288:
270:
251:
224:
214:
211:
199:
187:
166:
102:
90:
74:
39:
30:
29:
18:
1312:Blood tests
1203:Nitrogenous
1038:CPK-MB test
978:Lipid panel
913:Transferrin
861:Bicarbonate
856:Base excess
765:blood tests
343:osmolar gap
258:dehydration
158:osmolarity
144:osmolality
137:depression
126:osmometer (
1130:Conjugated
958:Metabolism
898:Serum iron
885:Iron tests
806:Creatinine
723:2009-03-05
552:2013-11-25
464:2009-03-04
401:Osmolality
388:References
353:osmolarity
349:osmolality
207:uricotelic
203:hypertonic
173:osmolality
169:osmolarity
93:osmolarity
45:osmolarity
41:Osmolality
16:Blood test
1120:Bilirubin
1070:Proteins
1048:Myoglobin
846:Anion gap
838:Acid-base
786:Potassium
631:CiteSeerX
588:0804-4643
514:0027-8424
336:Osmol gap
247:cytolysis
239:hypotonic
139:osmometer
131:osmometer
77:osmometer
1306:Category
1233:Proteins
1210:Azotemia
1142:Pancreas
928:Hormones
893:Ferritin
791:Chloride
699:11719745
653:10978027
596:20164214
548:. RNCEUS
532:24591588
445:14524639
366:See also
196:Nonhuman
147:mOsm/kg
65:solution
53:kilogram
1150:Amylase
875:Lactate
870:content
796:Calcium
604:9284617
523:3970477
492:Bibcode
316:ethanol
161:mOsm/L
112:Source
109:Origin
97:divisor
63:(L) of
57:solvent
49:osmoles
1155:Lipase
781:Sodium
697:
661:898032
659:
651:
633:
623:Stroke
602:
594:
586:
530:
520:
512:
443:
245:them (
243:lysing
179:Ranges
118:Units
1280:Other
657:S2CID
600:S2CID
266:urine
254:blood
184:Human
133:, or
61:liter
811:Urea
695:PMID
649:PMID
592:PMID
584:ISSN
528:PMID
510:ISSN
441:PMID
340:The
43:and
1241:LFT
1115:GGT
1103:AST
1098:ALT
1086:ALP
988:HDL
983:LDL
687:doi
641:doi
576:doi
572:162
518:PMC
500:doi
488:111
431:doi
403:,"
225:As
55:of
1308::
866:CO
693:.
683:38
681:.
669:^
655:.
647:.
639:.
627:31
625:.
621:.
598:.
590:.
582:.
570:.
526:.
516:.
508:.
498:.
486:.
482:.
439:.
427:23
425:.
421:.
286:.
141:)
83:.
868:2
756:e
749:t
742:v
726:.
701:.
689::
663:.
643::
606:.
578::
555:.
534:.
502::
494::
467:.
447:.
433::
399:"
213:(
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.