- 01A ratio ignores units only when both inputs convert the same way
Total cholesterol/HDL is 4.0 in mg/dL and in mmol/L, because both are cholesterol. Triglyceride/HDL is 3.0 in mg/dL but 1.3 in mmol/L, and the UK urea:creatinine ratio (with creatinine in mmol/L) runs about 4 times the US BUN/creatinine ratio, so a cut-off copied from the wrong unit system gives the wrong answer.
A lab prints a ratio when the balance between two markers tells it more than either number alone: harmful cholesterol against HDL (the protective cholesterol carried back to the liver), one liver enzyme against another, urea against creatinine. A ratio is one result divided by another, so it inherits both numbers' stories and both numbers' errors, and you can only read it well after you have looked at the two results underneath it.
Every common ratio at a glance
These are the ratios most people meet on a standard US or UK report. The cut-offs are typical adult values; your lab's own range on the report takes priority. The right-hand column shows which ratios change size between US and UK units.
| Ratio | What it hints at | Typical read | Units note |
|---|---|---|---|
| Total cholesterol/HDL | Harmful versus protective cholesterol | Under 3.5 good; over about 5 (men) or 4.5 (women) higher risk | Same number in mg/dL and mmol/L |
| Triglyceride/HDL | Insulin resistance | 3.0 or more flags it (mg/dL) | About 1.3 in mmol/L |
| ApoB/ApoA1 | Balance of harmful and protective particles | Lower is better; no single agreed cut-off | Same in g/L and mg/dL |
| AST/ALT | Pattern of liver injury | Under 1 usual in fatty liver or viral hepatitis; above 1 there can mean scarring; over 2 points toward alcohol | Unitless (both U/L) |
| BUN/creatinine | Kidney blood flow, protein load, bleeding | About 10 to 20 (US units) | UK urea:creatinine runs about 4 times larger, with creatinine in mmol/L |
| Albumin/globulin (A/G) | Protein balance, liver, inflammation | About 1.1 to 2.5 at many labs | Same in g/dL and g/L |
| Neutrophil/lymphocyte (NLR) | Stress and inflammation | About 0.8 to 3.5 in healthy adults | Unitless |
| Urine albumin/creatinine (ACR) | Protein leaking through the kidney | Under 3 mg/mmol (30 mg/g) | mg/g is about 8.8 times mg/mmol |
How to read any ratio in three steps
- 1Look at both inputs firstA ratio of 4.0 can come from total cholesterol 200 and HDL 50, or from 280 and 70. The second person has more cholesterol in total, and the ratio hides that. Check whether either input is flagged before you read the ratio.
- 2Check the unitsA ratio cancels units only when both inputs convert by the same factor. Total cholesterol and HDL are both cholesterol, so they convert by the same factor and the ratio is unchanged. Triglycerides convert by a different factor from HDL, so the triglyceride/HDL ratio changes size between mg/dL and mmol/L.
- 3Compare it with your own past ratiosA total cholesterol/HDL ratio that moves from 3.2 to 4.6 over three years tells you more than a single 4.6 sitting inside a range. See why a trend beats a single reading.
Here is the same lipid panel written in both unit systems. The total cholesterol/HDL ratio comes out at 4.0 in either unit, but the triglyceride/HDL ratio drops from 3.0 to 1.3, because 1 mmol/L of triglyceride is 88.6 mg/dL while 1 mmol/L of cholesterol is 38.7 mg/dL. The full conversion factors are on our lab units guide, and the cholesterol converter converts your own numbers.
| Result | US units (mg/dL) | UK and EU units (mmol/L) |
|---|---|---|
| Total cholesterol | 200 | 5.17 |
| HDL | 50 | 1.29 |
| Triglycerides | 150 | 1.69 |
| Total cholesterol/HDL | 200 / 50 = 4.0 | 5.17 / 1.29 = 4.0 |
| Triglyceride/HDL | 150 / 50 = 3.0 | 1.69 / 1.29 = 1.3 |
Cholesterol ratios: TC/HDL, LDL/HDL, TG/HDL and ApoB/ApoA1
The total cholesterol/HDL ratio divides all the cholesterol in your blood by the HDL. A lower ratio is better. The UK's QRISK3 heart-risk calculator uses this ratio as its only cholesterol input, rather than total or LDL cholesterol alone 1. A review of lipoprotein ratios put good at under about 3.5 and linked a ratio above about 5 in men and 4.5 in women to higher cardiovascular risk 2.
The LDL/HDL ratio works the same way with LDL on top. It runs lower than total cholesterol/HDL, and the same review treats values above about 3 to 3.5 (the lower figure for women) as raised risk 2. Some reports flip the ratio and print HDL as a share of total cholesterol: the same 4.0 ratio shows as 25%, and there a higher number is better.
Total cholesterol/HDL ratio: an example readingratio
If the ratio is high, the inputs tell you where to look: a low HDL points to low HDL, and a high total driven by triglycerides points to high triglycerides.
The triglyceride/HDL ratio is a stand-in for insulin resistance (when the body needs more insulin than normal to move sugar into cells). In overweight adults, a ratio of 3.0 or more in mg/dL picked out insulin resistance about as well as a fasting insulin test 3. In mmol/L, as UK and EU labs report it, the same cut-off is about 1.3.
The ApoB/ApoA1 ratio counts particles instead of cholesterol: ApoB sits on every harmful particle, ApoA1 on the protective ones. In the 52-country INTERHEART study, ApoB/ApoA1 was the strongest of the risk factors measured for a first heart attack, accounting for about 49% of the population-attributable risk 4. Guidelines still treat these ratios as risk markers rather than treatment targets; treatment targets stay with LDL, non-HDL and ApoB. For why ApoB often says more than any cholesterol figure, see ApoB vs LDL, and for the rest of the panel, how to read your lipid panel.
Your cholesterol ratios, in context
Two ratios that say more than any single number. Nothing leaves your browser.
Liver: the AST/ALT (De Ritis) ratio
The AST/ALT ratio divides one liver enzyme by the other; it carries the name of Fernando De Ritis, who described it in 1957. In fatty liver and viral hepatitis, ALT usually runs higher and the ratio sits below 1. An AST/ALT ratio above 2 points strongly toward alcohol-related liver disease 5. In fatty liver or chronic viral hepatitis, a ratio that rises above 1 can signal scarring (advanced fibrosis or cirrhosis) and should be raised with your clinician 5.
AST/ALT ratio: an example readingratio
Muscle injury raises AST (hard exercise can do it), and low vitamin B6 lowers ALT, so both can skew the ratio without any liver problem. The ratio only means much when at least one enzyme is raised; two normal enzymes give a ratio with nothing behind it. The liver enzymes guide and the high AST page cover the enzymes themselves. If raised liver enzymes come with yellow skin or eyes, dark urine or pale stools, get seen the same day.
Kidney and hydration: the BUN/creatinine ratio
The BUN/creatinine ratio divides blood urea nitrogen (a waste product of protein) by creatinine (a waste product of muscle). In US units the usual ratio is about 10 to 20. Because the kidney reabsorbs some urea but almost no creatinine, anything that slows blood flow to the kidney pushes the ratio up.
| Direction | Common reasons |
|---|---|
| High (over about 20) | Dehydration, heart failure, bleeding in the stomach or gut, a high-protein diet, steroid medicines, low muscle mass |
| Low (under about 10) | Low protein intake, liver disease, drinking a lot of fluid, pregnancy |
UK labs report urea in mmol/L and creatinine in µmol/L. To get the UK urea:creatinine ratio, convert creatinine to mmol/L first (divide by 1,000): urea 5 and creatinine 80 µmol/L gives 5 / 0.08 = about 62. That runs about 4 times the US BUN/creatinine figure, so a US 10 to 20 sits at roughly 40 to 80 in UK terms.
Creatinine runs low in people with little muscle, which pushes the ratio up without any kidney problem; cystatin C vs creatinine explains the alternative test. The pages for high BUN, a high BUN/creatinine ratio and a low BUN/creatinine ratio go through each cause. Both markers sit on the metabolic panel, and kidney function explained covers the whole renal panel.
CalculatorBUN to creatinine ratio calculatorWorks out the BUN/creatinine ratio from your report in US or UK units.Work it out Protein: the albumin/globulin (A/G) ratio
Globulins are the blood proteins other than albumin, mostly antibodies and carrier proteins. Most labs do not measure globulin directly; they calculate it as total protein minus albumin, then divide albumin by that figure. A typical A/G ratio is about 1.1 to 2.5 at many labs; use your lab's own range.
A low A/G ratio means albumin has fallen, globulin has risen, or both: liver disease, protein lost through the kidneys, long-running inflammation, or excess antibody production such as myeloma (a cancer of antibody-making plasma cells). Protein electrophoresis, a test that separates the blood proteins into bands, can check for that. A high A/G ratio usually reflects low globulin, which occasionally means a shortage of antibodies. The pages for high globulin and low albumin show which side moved.
Immune balance: the neutrophil-to-lymphocyte ratio (NLR)
The neutrophil-to-lymphocyte ratio divides the absolute neutrophil count by the absolute lymphocyte count, both taken from the breakdown of white cell types on a full blood count (CBC, or complete blood count). In 413 healthy adults, the NLR ran from about 0.78 to 3.53, with a mean near 1.65 6. Infection, surgery, acute stress, steroid medicines and a hard workout push neutrophils up and lymphocytes down, so the NLR can rise sharply within hours. A low NLR usually reflects a low neutrophil count, which can follow viral infections or some medicines; read the neutrophil count itself.
Use the NLR to follow a trend across several tests and read it beside the full differential. If your NLR is high and you were ill, stressed or had just trained hard, ask to repeat the CBC 2 to 4 weeks after you have recovered. If your absolute neutrophil count is very low and you have a fever, seek emergency care the same day. Use the absolute counts, and if your report only shows percentages, the absolute neutrophil count calculator converts them. The CBC guide and inflammation markers guide show where the NLR fits.
Read these beside the ratio
Urine and specialist ratios: ACR, PCR, aldosterone/renin and free/total PSA
Urine tests use ratios for a practical reason: a single urine sample can be dilute or concentrated depending on how much you drank. Dividing urine albumin or protein by urine creatinine corrects for that. International kidney guidelines treat a urine albumin/creatinine ratio of 3 mg/mmol (30 mg/g) or more as raised, a sign of kidney damage even when blood tests look normal. One raised ACR is usually repeated within 3 months before anyone calls it kidney damage. The urine protein/creatinine ratio does the same job for total protein.
Two blood ratios belong in specialist hands. The aldosterone/renin ratio screens for primary aldosteronism, a hormone cause of hard-to-control blood pressure; its cut-off depends on the assay and on blood pressure medicines taken beforehand. The free/total PSA ratio (PSA is prostate-specific antigen) is used when total PSA is borderline; a lower share of free PSA points more toward cancer than toward benign enlargement, and the cut-off a specialist uses depends on the assay and your age.
Fringe ratios: thyroid, cortisol and omega-3
Some ratios circulate online without agreed ranges. Free T3/free T4 is meant to show how well the body converts T4 into the active T3 hormone (T3 vs T4 explains the pair). TSH/free T4 is used in research on the thyroid's set point. Cortisol/DHEA-S is used in stress research (DHEA covers the hormone). None of the three has a range a lab or guideline stands behind, so read the individual results instead. Finger-prick fatty-acid tests also report an omega-6 to omega-3 ratio; our omega-3 page covers the omega-3 index and what the fish oil trials found.
Numbers labs calculate that are not ratios
Several results on a report are worked out from other results, and they behave like ratios in one way: an error in an input carries straight through. Each has its own calculator:
- Calculated LDL, from total cholesterol, HDL and triglycerides.
- eGFR, an estimate of how well your kidneys filter, from creatinine, age and sex.
- Calculated free testosterone, from total testosterone, SHBG and albumin.
- HOMA-IR, an estimate of insulin resistance from fasting glucose and insulin.
- Transferrin saturation: serum iron as a share of the blood's iron-carrying capacity.
- Anion gap, a check on the blood's acid balance, and corrected calcium, which adjusts calcium for albumin.
When a ratio misleads you
A ratio hides which number moved. The two people below have almost the same non-HDL cholesterol (the cholesterol in harmful particles), yet their total cholesterol/HDL ratios look like opposite results because one has very high HDL.
| Person A | Person B | |
|---|---|---|
| Total cholesterol (mg/dL) | 240 | 190 |
| HDL (mg/dL) | 90 | 38 |
| Non-HDL (mg/dL) | 150 | 152 |
| Total cholesterol/HDL | 2.7 | 5.0 |
Person A's 2.7 looks excellent, but the cholesterol in harmful particles is the same as Person B's. Ratios also double the noise: each input wobbles a little from day to day, so the ratio wobbles more than either one. Fasting status, a recent infection and the units on the report all shift ratios too, as the reference ranges guide explains.
- Both inputs normal: the ratio rarely adds anything new.
- One input extreme: read that input, not the ratio.
- A ratio with no agreed range: treat it as a curiosity until research settles a range.
- A ratio compared across labs or countries: check the units first.
What to do with a flagged ratio
- 1Find which input movedOpen the page for the flagged input and read that first.
- 2Cholesterol ratios highIf total cholesterol/HDL is over about 5, or triglyceride/HDL is high, ask your clinician for a heart-risk score and an ApoB test, plus HbA1c if triglyceride/HDL is high.
- 3AST/ALT over 2, or above 1 with known liver diseaseBe open with your clinician about alcohol and ask whether a liver ultrasound or a scarring check is needed.
- 4Urine ACR raisedAsk for a repeat within 3 months, because one raised result does not confirm kidney damage.
- 5Retest the same wayUse the same lab and the same units next time so the trend is a fair comparison.
Citations
- Hippisley-Cox J, Coupland C, Brindle P. Development and validation of QRISK3 risk prediction algorithms to estimate future risk of cardiovascular disease. BMJ 2017;357:j2099
- Millán J et al. Lipoprotein ratios: physiological significance and clinical usefulness in cardiovascular prevention. Vasc Health Risk Manag 2009;5:757-765
- McLaughlin T et al. Use of metabolic markers to identify overweight individuals who are insulin resistant. Ann Intern Med 2003;139:802-809
- Yusuf S et al. Effect of potentially modifiable risk factors associated with myocardial infarction in 52 countries (the INTERHEART study). Lancet 2004;364:937-952
- Botros M, Sikaris KA. The De Ritis ratio: the test of time. Clin Biochem Rev 2013;34:117-130
- Forget P et al. What is the normal value of the neutrophil-to-lymphocyte ratio? BMC Res Notes 2017;10:12
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.
