Iono360
Fluid and electrolyte disorders.
Overview
Iono360 organises the interpretation of adult fluid and electrolyte disorders around sodium, potassium and calcium. The approach distinguishes biochemical measurements, calculated estimates, possible mechanisms and the information required for clinical assessment.
How to use
The space is in preparation. This page presents its method and references. Depending on the question, interpretation combines blood and urine results with their sampling conditions.
Method and limitations
Which laboratory information should be retained?
A measurement comprises a value, unit, result type and the available information about method, specimen and time. These elements determine which results can be combined. Treatment or an intervention between samples may affect comparability.
A value reported as “less than” or “greater than” a bound is not equal to that bound. Classification is certain only when compatible values lead to the same category. Rounding improves readability without replacing the precision of the reported result.
How does glucose affect sodium interpretation?
The depth of a sodium abnormality and its clinical impact are separate questions. “Profound hyponatraemia” describes a concentration; symptoms and clinical circumstances provide another dimension of assessment. Published hypernatraemia categories also retain their context rather than representing universal physiological thresholds. [I1–I3]
In hyperglycaemia, the Katz and Hillier models estimate sodium at a reference glucose. They help examine the possible contribution of glucose to the observed concentration. The estimate depends on the model and its assumptions; it replaces neither measured sodium nor assessment of tonicity. [I6, I7a, I7b]
Why distinguish osmolality, osmolarity and tonicity?
Measured osmolality is a laboratory result expressed per kilogram. Calculated osmolarity is an estimate per litre. With concentrations in mmol/L, the convention described here uses:
Calculated osmolarity = 2 × measured sodium + glucose + urea.
Estimated effective tonicity uses:
Estimated tonicity = 2 × measured sodium + glucose.
Including or excluding urea distinguishes these calculations. Neither represents every possible osmole; the formula and quantity name remain necessary for interpretation. [I1, I8]
The osmolal gap conventionally compares measured osmolality with calculated osmolarity, using an approximation between their units. Classification requires a reference compatible with the method and formula. A gap does not identify a substance, and a value within the reference interval does not exclude poisoning. [I8]
What do urine results add?
In hypotonic hyponatraemia, urine osmolality informs dilution and antidiuresis. Urine sodium then contributes to reasoning alongside treatment and context; it does not establish SIAD alone. In hypernatraemia, urine concentration and volume must be distinguished: dilute urine does not establish polyuria without documented output. [I1, I2]
For potassium, a spot concentration, potassium-to-creatinine ratio and excreted amount are not interchangeable. The ratio requires the same sample; a collected amount requires a representative concentration and volume; interpretation over a specified period requires a corresponding collection. Diuretics, supplementation, kidney function and collection quality may affect interpretation. [I9]
How do potassium, ECG and monitoring relate?
The biochemical category describes potassium concentration. An ECG assesses cardiac effects; continuous monitoring has a separate indication. These three pieces of information remain distinct. Hypokalaemia sources retain their general or cardiovascular context. [I4, I5]
For hyperkalaemia, the cited UKKA recommendations concern hospitalised adults: 14.1 addresses ECG and 14.2 continuous monitoring. A normal ECG does not exclude risk. A conditional recommendation does not establish that its condition is present, and a biochemical panel alone does not demonstrate clinical stability. [I10]
Which calcium result is reported?
Measured total calcium, measured ionised calcium and laboratory-reported albumin-adjusted calcium are different results. Total calcium does not directly establish the ionised fraction. The approach described here does not automatically calculate an albumin adjustment. [I12, I13]
When calcium status determines a clinical decision or total calcium is difficult to interpret, ionised calcium helps clarify the situation, subject to sampling and pH requirements. Ionised calcium adjusted to pH 7.40 remains distinct from measurement at actual pH. Published emergency reference points based on adjusted calcium are not transferred numerically to total or ionised calcium. [I13–I16]
What do the additional calculations provide?
The chemistry anion gap uses sodium, chloride and chemistry total CO₂, without potassium. Blood gas bicarbonate is a different analytical input. Albumin adjustment of the anion gap remains a separately named estimate, interpreted against an appropriate reference. [I17]
CKD-EPI 2021 eGFR estimates adult glomerular filtration under the equation’s conditions. Interpretation is limited particularly when creatinine is changing. A single value establishes neither chronic kidney disease, acute kidney injury nor potassium excretion capacity. [I18, I19]
Two compatible measurements allow a dated comparison; they do not automatically demonstrate a continuous trajectory or chronicity. Each conclusion retains its required inputs. An incomplete panel can therefore provide useful information without supporting every interpretation.
References
References are grouped by clinical question. Their comments distinguish guidelines, studies and models, together with the conditions governing their use.
Sources
Full references
Spasovski G, Vanholder R, Allolio B, et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. European Journal of Endocrinology. 2014;170:G1–G47. DOI 10.1530/EJE-13-1020. NDT copublication, DOI 10.1093/ndt/gfu040.
Hyponatraemia guideline: concentration, hypotonicity and urine assessment. Low sodium alone does not establish tonicity; the EJE and NDT accesses carry the same guideline.
Yun G, Baek SH, Kim S. Evaluation and management of hypernatremia in adults: clinical perspectives. Korean Journal of Internal Medicine. 2023;38(3):290–302, online December 2022. DOI 10.3904/kjim.2022.346.
Clinical review of adult hypernatraemia: diagnostic steps and urine concentration/volume. Urine osmolality alone does not establish the cause.
Arzhan S, Roumelioti ME, Litvinovich I, Bologa CG, Unruh ML. Outcomes of Hospital-Acquired Hypernatremia. Clinical Journal of the American Society of Nephrology. 2023;18(11):1396–1407. DOI 10.2215/CJN.0000000000000250.
Observational study of hospital-acquired hypernatraemia. Its categories and associations concern that population, without a universal individual-risk estimate.
Kim MJ, Valerio C, Knobloch GK. Potassium Disorders: Hypokalemia and Hyperkalemia. American Family Physician. 2023;107(1):59–70. PMID 36689973.
Clinical review: initial assessment and the role of ECG in potassium disorders. Biochemical classification and assessment of urgency remain distinct.
Krogager ML, Kragholm K, Thomassen JQ, et al. Update on management of hypokalaemia and goals for the lower potassium level in patients with cardiovascular disease: a review in collaboration with the European Society of Cardiology Working Group on Cardiovascular Pharmacotherapy. European Heart Journal – Cardiovascular Pharmacotherapy. 2021;7:557–567. DOI 10.1093/ehjcvp/pvab038.
Specialist review of hypokalaemia reference points in cardiovascular care. It is not a universal guideline for all populations.
Katz MA. Hyperglycemia-induced hyponatremia—calculation of expected serum sodium depression. New England Journal of Medicine. 1973;289(16):843–844. DOI 10.1056/NEJM197310182891607.
Original Katz model publication. Estimation at reference glucose is conditional and does not replace measured sodium.
Hillier TA, Abbott RD, Barrett EJ. Hyponatremia: evaluating the correction factor for hyperglycemia. American Journal of Medicine. 1999;106(4):399–403. DOI 10.1016/S0002-9343(99)00055-8.
Experimental study of the Hillier factor. An alternative model without established universal superiority.
Umpierrez GE, Davis GM, ElSayed NA, et al. Hyperglycemic Crises in Adults With Diabetes: A Consensus Report. Diabetes Care. 2024;47(8):1257–1275. DOI 10.2337/dci24-0032.
Adult hyperglycaemic-crisis consensus, including the sodium/glucose discussion on p.1265. A publication distinct from the Hillier study.
Choy KW, Wijeratne N, Lu ZX, Doery JCG. Harmonisation of Osmolal Gap – Can We Use a Common Formula? Clinical Biochemist Reviews. 2016;37:113–119.
Methodological review of osmolal-gap formulae. Formula and reference govern interpretation; the gap alone does not identify a substance.
Kardalas E, Paschou SA, Anagnostis P, Muscogiuri G, Siasos G, Vryonidou A. Hypokalemia: a clinical update. Endocrine Connections. 2018;7:R135–R146. DOI 10.1530/EC-18-0109.
Hypokalaemia review: urine potassium, creatinine ratio and timed collections. Conditional reference points without automatically establishing a renal cause.
UK Kidney Association. Treatment of Acute Hyperkalaemia in Adults — Updated July 2026. Professional guideline, EN.
UKKA, July 2026 edition: recommendation 14.1 for ECG and 14.2 for continuous monitoring, pp.13–14. Separate supporting recommendations for adult inpatient care.
Desgagnés N, King JA, Kline GA, Seiden-Long I, Leung AA. Use of Albumin-Adjusted Calcium Measurements in Clinical Practice. JAMA Network Open. 2025;8:e2455251. DOI 10.1001/jamanetworkopen.2024.55251.
Study comparing total calcium, albumin adjustments and ionised calcium in clinical practice. Addresses adjustment limitations without establishing ECG or monitoring thresholds.
Cavalier E, Zima T, Plebani M, et al. Albumin-adjusted (“corrected”) calcium should no longer be reported: a position statement from the Joint IOF Working Group and IFCC Committee on Bone Metabolism and EFLM Committee on CKD. Clinical Chemistry and Laboratory Medicine. 2026;64(8):1719–1721. DOI 10.1515/cclm-2026-0545.
IOF/IFCC/EFLM position on calcium reporting and ionised calcium, including actual pH. An attributed position without a claim of universal consensus.
Turner J, Gittoes N, Selby P; Society for Endocrinology Clinical Committee. Emergency management of acute hypocalcaemia in adult patients. Endocrine Connections. 2016;5:G7–G8. DOI 10.1530/EC-16-0056.
2016 adult emergency guidance: hypocalcaemia reference points tied to adjusted calcium. No numerical transfer to total or ionised calcium.
Turner J, Gittoes N, Selby P. Society for Endocrinology Emergency Endocrine Guidance: Emergency management of acute hypocalcaemia in adult patients. Endocrine Connections. 2019;8:X1. DOI 10.1530/EC-16-0056a.
2019 addendum read alongside the 2016 document. It retains its own bibliographic identity.
Walsh J, Gittoes N, Selby P. Society for Endocrinology Endocrine Emergency Guidance: Emergency management of acute hypercalcaemia in adult patients. Endocrine Connections. 2016;5:G9–G11. DOI 10.1530/EC-16-0055.
Adult emergency hypercalcaemia guidance within its adjusted-calcium framework. Reference points remain dependent on the analytical quantity.
Jung B et al. Diagnosis and management of metabolic acidosis: guidelines from a French expert panel. Annals of Intensive Care, 2019. DOI 10.1186/s13613-019-0563-2.
Expert guidance, R1.3: anion gap and albumin-adjusted estimate. An appropriate reference is required; no automatic equivalence between blood gas and chemistry AG.
National Institute of Diabetes and Digestive and Kidney Diseases.
Institutional presentation of adult eGFR equations, including CKD-EPI 2021. eGFR remains an estimate subject to the equation’s conditions.
KDIGO. 2024.
KDIGO 2024: G categories in Table 2 and evidence of chronicity in practice points 1.1.3.1–2. A single estimate does not establish CKD.