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- [ALT (SGPT) blood test checker](/alt-blood-test) grades an ALT result against the ACG "healthy" upper limits, explains the R-ratio pattern of liver injury, and links to FIB-4 for fibrosis risk.
- [BMP blood test explainer](/bmp-blood-test) covers all eight tests in a basic metabolic panel – glucose, calcium, sodium, potassium, chloride, bicarbonate, BUN and creatinine – with the anion gap calculated from your own results.
Which electrolyte or liver tool do you need?
Electrolytes, minerals and liver tests are reported together on a comprehensive metabolic panel. Several important clinical calculations combine these values. This section covers:
- [Anion gap calculator](/anion-gap-calculator) – sodium − (chloride + bicarbonate), with albumin correction, to investigate metabolic acidosis.
- [Corrected calcium calculator](/corrected-calcium-calculator) – adjusts total calcium for a low albumin (Payne formula).
- [Corrected sodium calculator](/corrected-sodium-calculator) – adjusts sodium for high glucose (Hillier and Katz factors).
- [Serum osmolality calculator](/serum-osmolality-calculator) – 2 × Na + glucose + urea, with the osmolal gap.
- [FIB-4 calculator](/fib-4-calculator) – estimates the risk of advanced liver fibrosis from age, AST, ALT and platelets.
- Converters for calcium, magnesium, phosphate, albumin and bilirubin.
Key formulas at a glance
| Calculation | Formula | Typical normal |
|---|---|---|
| Anion gap | Na − (Cl + HCO₃) | about 3–11 mmol/L (lab-dependent) |
| Albumin-corrected anion gap | AG + 2.5 × (4.0 − albumin g/dL) | as above |
| Corrected calcium | Ca + 0.8 × (4.0 − albumin g/dL) | 8.6–10.3 mg/dL (2.15–2.58 mmol/L) |
| Corrected sodium | Na + 2.4 × (glucose − 100) ÷ 100 | 135–145 mmol/L |
| Calculated osmolality | 2 × Na + glucose/18 + BUN/2.8 | 275–295 mOsm/kg |
| Osmolal gap | Measured − calculated osmolality | below about 10 mOsm/kg |
| FIB-4 | (age × AST) ÷ (platelets × √ALT) | below 1.30 (below 2.0 if 65+) |
Why corrections matter
Several blood results are influenced by other values on the same panel:
- Albumin carries calcium and contributes most of the normal anion gap. When albumin is low – common in hospital patients and in liver or kidney disease – total calcium and the anion gap fall, potentially hiding real problems.
- Glucose draws water out of cells when very high, diluting sodium. Corrected sodium reveals the true water balance in diabetic emergencies.
- Unmeasured substances such as alcohols raise measured osmolality but not the calculated value, creating an osmolal gap.
These corrections are approximations. When precision matters, clinicians measure ionised calcium directly, use blood gas analysers and interpret results in context.
Liver tests in brief
ALT and AST are enzymes released from damaged liver cells; alkaline phosphatase and GGT rise with bile duct problems; bilirubin reflects the liver's ability to process the breakdown products of red cells; albumin reflects liver synthetic function and nutrition. FIB-4 combines AST, ALT, age and platelets to estimate scarring – the key predictor of long-term outcomes in fatty liver disease, which is now called metabolic dysfunction-associated steatotic liver disease (MASLD).
When to seek medical advice
These calculations are mainly used by clinicians to interpret blood tests, often in hospital. Discuss abnormal results with your clinician. Seek emergency care for confusion, seizures, rapid breathing, severe vomiting, suspected poisoning (for example antifreeze or methanol), or yellowing of the skin with abdominal swelling or vomiting blood.
Frequently asked questions
Do I need to correct calcium if my lab reports "adjusted calcium"?
No. Adjusted calcium is already corrected using the laboratory's own formula.
What does a high anion gap mean?
It usually indicates a build-up of acids such as lactate or ketones, kidney failure, or certain poisonings.
Is a FIB-4 below 1.30 reassuring?
Yes, for adults aged 35–64 it makes advanced fibrosis unlikely. From age 65, the low-risk cut-off is 2.0.
Sources
- Kraut JA, Madias NE. Serum anion gap: its uses and limitations in clinical medicine. Clin J Am Soc Nephrol 2007
- Hillier TA, Abbott RD, Barrett EJ. Hyponatremia: evaluating the correction factor for hyperglycemia. Am J Med 1999
- Rinella ME, et al. AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease. Hepatology 2023