Quick guide to get you started with Medical Biochemistry Assistant
Calc Tab: Browse and open clinical calculators. Enter values
and results appear instantly. Click unit badges to switch between units.
QC Tab: Upload and analyze quality control data with
Levey-Jennings charts, Westgard rules, and statistical summaries. Includes PBRTQC, RCV, Sigma
metric, and Carryover analysis tools.
Guide Tab: Reference guides, clinical ranges, and
interpretation notes for laboratory parameters. Fetch the latest articles from leading journals
via PubMed integration.
Notes Tab: Save personal notes and observations. Your data
stays in your browser's local storage.
Pro Tips: Hover over buttons for explanations. Use the
Clear All button to reset a calculator. Click Info & Guide
inside calculators for clinical context.
MEDICAL BIOCHEMISTRY ASSISTANT
Professional Laboratory Tool
Spot Urine Analysis
Used as a rapid screening tool to estimate daily protein excretion using the Protein/Creatinine
ratio when 24-hour collection is impractical. Highly correlated with total protein loss in
diabetic nephropathy screening and preeclampsia monitoring; however, results can be misled by
orthostatic proteinuria or exercise if the first morning void is not used.
mg/dL
mg/dL
U/L
mg/dL
mg/dL
mEq/L
µg/L
mg/dL
mEq/L
mg/dL
mEq/L
mg/dL
mg/dL
µg/dL
mg/dL
mg/L
mg/L
mg/L
mg/L
µg/L
µg/L
µg/L
µg/L
µg/L
µg/L
µg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
Calculation Method (Spot Urine Ratios):
Analyte Ratio = (Spot Analyte ÷ Spot Creatinine) × Factor *Factors: 1000 for mg/g Cr, 100 for mEq/g, U/g, or µg/g
Cr.
Manual Dilution Planner
A laboratory optimization tool used to accurately calculate the required volumes for diluting
high-concentration samples that exceed the instrument's linearity range. This is not a
diagnostic test but a process tool to ensure result accuracy by minimizing manual pipetting or
calculation errors.
µL
Recipe adjusts to
ensure at least this amount of sample is used.
(If
not listed above)
(Enter
to see final result)
24-Hour Urine Calculation
The gold standard for the definitive assessment of proteinuria and renal function (creatinine
clearance) when nephrotic syndrome or kidney failure is suspected. It clarifies total daily loss
to guide treatment decisions like biopsy or drug dosing; however, patient compliance is critical
as collection errors directly invalidate the results.
Cockcroft DW, et al. Prediction of creatinine clearance from serum creatinine.
Nephron. 1976. (PMID: 1244564)
Rostoker G, et al. Estimating glomerular filtration rate from serum creatinine and
blood urea nitrogen. Sci Rep. 2021. (PMID: 34158525)
mL
mg/dL
U/L
mg/dL
mg/dL
mEq/L
mEq/L
µg/L
mg/dL
mg/dL
mEq/L
mg/dL
mg/dL
mg/dL
mg/L
mg/L
mg/L
µg/L
mg/L
mg/L
mg/L
mg/L
µg/L
µg/L
µg/L
µg/L
µg/L
µg/L
µg/L
Calculation Method (24h Excretion):
Daily Excretion = Urine Concentration × Urine Volume × 0.01 (Factor for mg/dL to mg/day) *Results are normalized to total volume provided. Matched
units (e.g., mg/day, mEq/day) are displayed.
A fundamental parameter for staging chronic kidney disease and adjusting drug dosages by
estimating actual filtration rather than relying solely on creatinine. Highly sensitive for
early detection of renal decline, but may be unreliable in dynamic processes like acute kidney
injury where creatinine levels are not in steady-state.
Levey AS, et al. A new equation to estimate glomerular filtration rate. Ann Intern
Med. 2009. (PMID: 19414839)
Inker LA, et al. New Creatinine- and Cystatin C–Based Equations to Estimate GFR
without Race. N Engl J Med. 2021. (PMID: 34554658)
Female
Male
Non-Black /
Other
Black
Year
kg
mg/dL
mg/L
Low-Density Lipoprotein (LDL) Calculator
Used in routine lipid panels to manage coronary artery disease risk and set statin therapy
goals. Calculated from total cholesterol, HDL, and triglycerides; however, the formula becomes
mathematically invalid if triglycerides exceed 400 mg/dL, requiring direct LDL measurement.
Friedewald WT, et al. Estimation of the concentration of low-density lipoprotein
cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem.
1972. (PMID: 4337382)
Martin SS, et al. Comparison of a novel method vs the Friedewald equation for
estimating LDL cholesterol levels. JAMA. 2013. (PMID: 24240933)
mg/dL
mg/dL
mg/dL
Homeostatic Model Assessment for Insulin
Resistance (HOMA-IR)
Quantitatively assesses insulin resistance at the tissue level, even before a diabetes diagnosis
is made. Valuable for early risk determination in metabolic syndrome or PCOS; however, the
calculation is invalid in patients using exogenous insulin or those with exhausted beta-cell
reserves.
Matthews DR, et al. Homeostasis model assessment: insulin resistance and beta-cell
function from fasting plasma glucose and insulin concentrations in man.
Diabetologia. 1985. (PMID: 3899825)
Wallace TM, et al. Use and abuse of HOMA modeling. Diabetes Care. 2004. (PMID:
15163354)
mg/dL
µIU/mL
Schwartz Formula (Pediatric GFR)
Bedside Schwartz Equation (Revised 2009):
Used for children aged 1-16 years: eGFR = 0.413 × [Height (cm) / Serum Creatinine
(mg/dL)]
IDMS Requirement:
This formula applies to enzymatic serum creatinine measurements calibrated to reference
measurements by isotope dilution mass spectroscopy (IDMS), but not to alkaline picrate
("Jaffe") methods, even those traceable to IDMS. (For more information see National Kidney
Disease Education Program.)
Original Schwartz (Jaffe-based) Constants (k):
If using older Jaffe methods, the formula eGFR = k × [Height / Scr] applies with
specific constants:
Preterm infants: k = 0.33
Full-term infants (<1 year): k=0.45
Children and adolescent girls: k = 0.55
Adolescent boys: k = 0.70
Important Considerations:
- Enzymatic creatinine assays are preferred in children because non-creatinine chromogens
can cause significant errors at low creatinine values.
- The formula may overestimate GFR, especially in patients with low muscle mass or at lower
GFR levels.
- Accuracy significantly decreases when GFR > 103 mL/min/1.73m².
References:
Schwartz GJ, et al. New equations to estimate GFR in children with CKD. J Am Soc
Nephrol. 2009.
Schwartz GJ, et al. The use of plasma creatinine concentration for estimating
glomerular filtration rate in infants, children, and adolescents. Pediatr Clin North
Am. 1987.
Counselman FL, et al. Comparison of the glomerular filtration rate in children by
the new revised Schwartz formula and a new generalized formula. Kidney Int. 2013.
Bedside Schwartz Equation - Dr. Oracle Medical Advisory Board.
Original Schwartz
Revised Bedside Schwartz
Preterm (0.33)
Term Infant (0.45)
Child (0.55)
Adolescent Girl (0.55)
Adolescent Boy (0.70)
mg/dL
cm
Fibrosis-4 (FIB-4) Score
A non-invasive screening tool for advanced liver fibrosis risk in patients with fatty liver
disease (NAFLD). High reliability in excluding cirrhosis to prevent unnecessary biopsies; Note
that scores naturally increase with age, and the exclusion threshold may be higher in patients
over 65.
Sterling RK, et al. Development of a simple noninvasive index to predict significant
fibrosis in patients with HIV/HCV coinfection. Hepatology. 2006. (PMID: 16729309)
Vallet-Pichard A, et al. FIB-4: an inexpensive and accurate marker of fibrosis in
HCV patients. Hepatology. 2007. (PMID: 17351610)
Year
10³/µL
U/L
U/L
D-Dimer Universal Converter
Standardizes D-Dimer results between potentially different laboratory units (FEU vs. DDU) to
prevent misinterpretation in VTE/PE exclusion. Mixing up units can lead to unnecessary
anticoagulation or missed diagnoses; unit confirmation is mandatory before clinical decisions.
Fibrinogen Equivalent Units (FEU)
D-Dimer Units (DDU)
1 DDU = 2 x FEU | Örn: 250 ng/mL DDU = 500 ng/mL FEU
Smart Dilution Planner
Used in medical laboratories to calculate stepwise dilution ratios needed for antibody titer
determination or analysis of highly concentrated samples. This is an analytical process tool,
not a diagnostic test; the accuracy of the prepared solutions directly impacts the reliability
of the final result.
Enter
the
starting concentration of your source solution.
(Optional)
The
system will
find the best path to reach this value.
µL
Volume
to be
pipetted from the previous tube in each step.
*If blank, 100 µL is used
automatically.
Corrected Sodium
Vital in evaluating severe hyperglycemia (DKA/HHS) to distinguish if low sodium is a true
deficiency or a dilutional (pseudohyponatremia) effect of glucose. This prevents inappropriate
saline replacement and associated risks of cerebral edema while predicting the sodium rise
during treatment.
Katz MA. Hyperglycemia-induced hyponatremia--calculation of expected serum sodium
depression. N Engl J Med. 1973. (PMID: 4763428)
Hillier TA, et al. Hyponatremia: evaluating the correction factor for hyperglycemia.
Am J Med. 1999. (PMID: 10225241)
mEq/L
mg/dL
Corrected Calcium
Identifies "pseudohypocalcemia" in patients with hypoalbuminemia (malnutrition, malignancy).
Even if total calcium appears low, physiologically active calcium may be normal. If blood pH is
abnormal, albumin binding changes and this formula loses reliability; in such cases, ionized
calcium measurement is the gold standard.
mg/dL
g/dL
Corrected Magnesium
Distinguishes whether low magnesium levels in hypoalbuminemic patients represent a true
deficiency or merely a decrease in the carrier protein. Critical for identifying real magnesium
deficits in cases of refractory hypocalcemia or hypokalemia, although its clinical validation is
less definitive than corrected calcium.
mg/dL
g/dL
Serum Anion Gap
In metabolic acidosis of unknown origin, this determines if the cause is acid addition (High AG
- e.g., ketoacidosis, lactate) or bicarbonate loss (Normal AG - e.g., diarrhea). In the presence
of hypoalbuminemia, the calculated value will be misleadingly low; therefore, a correction
factor must be added for every 1 g/dL drop in albumin.
Oh MS, et al. The anion gap. N Engl J Med. 1977. (PMID: 895822)
Figge J, et al. Anion gap and hypoalbuminemia. Crit Care Med. 1998. (PMID: 9824071)
mEq/L
mEq/L
mEq/L
g/dL
Serum Osmolality & Osmolal Gap
Checks for the presence of an "osmolal gap" by comparing calculated and measured osmolality.
This is critical for detecting alcohol (ethanol, methanol, ethylene glycol) poisoning. A normal
gap (<10) helps exclude toxic ingestion; note that if ethanol is not included in the formula,
the gap will appear artificially high in patients who have consumed alcohol.
mEq/L
mg/dL
mg/dL
mg/dL
mOsm/kg
Fractional Excretion of Sodium (FENa)
Differentiates between prerenal azotemia (<1%) and acute tubular necrosis (>2%) in oliguric
acute kidney injury by measuring the kidney's sodium-retaining ability. Result is
invalid in
patients using diuretics because sodium excretion is disrupted; in those cases,
Fractional
Excretion of Urea (FEUrea) should be used instead.
Espinel CH. The FENa test. Use in the differential diagnosis of acute renal
failure. JAMA. 1976. (PMID: 947230)
Miller TR, et al. Urinary diagnostic indices in acute renal failure: a
prospective study. Ann Intern Med. 1978. (PMID: 666184)
mEq/L
mg/dL
mEq/L
mg/dL
Serum-Ascites Albumin Gradient (SAAG)
In patients with ascites, this more clearly distinguishes between portal hypertension (e.g.,
cirrhosis, heart failure) and peritoneal involvement (e.g., cancer, tuberculosis) than
Light's
criteria. A difference >1.1 g/dL indicates portal hypertension; blood and fluid samples must
be
taken simultaneously for accurate results.
g/dL
g/dL
Pleural Fluid pH Estimation
Used to estimate the acidity of the environment via the Henderson-Hasselbalch equation when
blood
gas analyzers are unavailable or for pleural/ascitic fluid analysis. While it provides a
quick
idea, it is not as precise or reliable as a dedicated blood gas device for directing
treatment
in critical acidosis or alkalosis.
mmol/L
mmHg
Mentzer Index
A screening tool for microcytic anemia (low MCV) to distinguish between simple iron
deficiency
and genetic Thalassemia trait. An index >13 favors iron deficiency, while <13 favors
thalassemia; note that results are unreliable in patients who have both conditions
simultaneously.
fL
10⁶/µL
Albumin/Globulin Ratio
Used to understand the direction of unexplained total protein changes. A low ratio (<1)
helps distinguish between increased globulin production (Multiple Myeloma, chronic
infection, autoimmunity) and selective albumin loss (nephrotic syndrome). Should be
interpreted alongside the patient's hydration status, as dehydration can mask
changes.
g/dL
g/dL
Red Blood Cell (RBC) Indices
Derived from hemoglobin, hematocrit, and red cell count for the morphological
classification of
anemia (microcytic, normocytic, macrocytic). Fundamental for manual control or when
automated
counters are unavailable; however, the count and calculation will be distorted in
the presence
of cold agglutinins.
g/dL
%
10⁶/µL
Corrected Reticulocyte Count
Evaluates whether the bone marrow is responding appropriately to anemia
(regenerative vs. hypoproliferative). The raw reticulocyte percentage can look
misleadingly high due to a low hematocrit; this calculation provides the
"reticulocyte production index" to reveal the marrow's true performance.
%
%
%
International Normalized Ratio
(INR) Calculator
Standardizes prothrombin time (PT) results across different laboratories to manage
bleeding or clotting risks, especially for patients on warfarin. Essential for
dosage adjustment; note that INR can be elevated in liver failure even without
anticoagulants, which may not perfectly reflect bleeding risk.
sec
sec
-
Blood Urea Nitrogen
(BUN)/Creatinine Ratio
Differentiates between prerenal causes (dehydration, heart failure) and renal
parenchymal damage in acute kidney injury. A ratio >20 strongly supports prerenal
azotemia or increased protein load (e.g., GI bleed); however, steroid use and
catabolic states can also raise the ratio independently of renal function.
mg/dL
mg/dL
Arterial Blood Gas (ABG)
Validation [H+]
A laboratory quality control tool that tests the technical reliability of blood gas
results by checking the mathematical balance (Henderson-Hasselbalch) between pH,
pCO2, and HCO3. It helps detect instrument errors or improper sample handling before
clinical intervention.
mmHg
mmol/L
Free Androgen Index (FAI)
In women suspected of PCOS or hirsutism, this is more sensitive than total
testosterone for detecting bioavailable androgen excess. It reveals androgen effects
linked to low SHBG; however, its use in men is typically not clinically significant.
ng/dL
nmol/L
g/dL
Free Prostate-Specific Antigen
(PSA) %
Used to distinguish cancer risk from benign prostatic hyperplasia (BPH) when total
PSA is in the "gray zone" (4-10 ng/mL). A low ratio (<10-15%) favors cancer; note
that acute prostatitis or recent ejaculation can cause false positives.
ng/mL
ng/mL
Transtubular Potassium
Gradient
(TTKG)
Determines whether the cause of hypokalemia or hyperkalemia is renal or
extrarenal by
evaluating aldosterone activity in the distal nephron. Reliable only when urine
osmolality is greater than plasma; otherwise, the formula is physiologically
invalid and should not be interpreted.
mmol/L
mmol/L
mOsm/kg
mOsm/kg
mmol/L
Ethanol (Promil/Driving)
Calculator
Converts Serum Ethanol (mg/dL) to Promil (‰).
Legal Note: Legal limit for private drivers in Turkey is
0.50 Promil (50 mg/dL). For commercial drivers, it is 0.20 Promil (20 mg/dL).
mg/dL
‰
Estimated Ionized Calcium
Estimated biologically active calcium level when blood gas devices are
unavailable.
Helpful when total calcium levels do not match symptoms like tetany or
paresthesia;
however, it remains an estimate as it does not account for pH-driven changes in
albumin binding.
mg/dL
g/dL
Ref: 4.4–5.3 mg/dL
Immunoglobulin G (IgG) Index
Evidence of intrathecal immunoglobulin synthesis (inflammation) in the central
nervous system, independent of blood-brain barrier dysfunction. Highly
suggestive of
Multiple Sclerosis, but must be evaluated alongside oligoclonal bands and
clinical
findings for a definitive diagnosis.
mg/dL
g/dL
mg/dL
mg/dL
Transferrin Saturation
A first-line parameter for distinguishing iron deficiency from anemia of chronic
disease and screening for hemochromatosis. Low values indicate iron deficiency,
while high values (>45%) suggest toxic tissue accumulation; note that
inflammation
suppresses transferrin production, potentially causing false high saturation.
µg/dL
µg/dL
Light's Criteria (Pleural
Effusion)
Distinguishes between "transudates" (due to conditions like heart failure) and
"exudates" (resulting from infection or cancer) in pleural effusion cases with
98% sensitivity. In heart failure patients receiving diuretics, fluid may
concentrate and mimic an exudate; in such instances, the serum-pleural albumin
gradient should be assessed.
Light RW, et al. Pleural effusions: the diagnostic separation of
transudates and exudates. Ann Intern Med. 1972. (PMID: 4642738)
g/dL
g/dL
U/L
U/L
U/L
Polyethylene Glycol (PEG)
Recovery
Detects Macroprolactinemia, Macroamylasemia, and other macro-enzyme complexes.
Polyethylene Glycol (PEG) precipitates large immune complexes. A recovery < 40%
typically indicates the presence of a macro-complex (e.g., Macroprolactin),
while> 50-60% usually indicates monomeric (true) hormone/enzyme.
conc
conc
Fractional Excretion of Urea
(FEUrea)
Useful when FENa is unreliable due to diuretic use. <35% indicates Prerenal
etiology;>50% suggests Acute Tubular Necrosis (ATN).
Predicts risk of progression to kidney failure requiring
dialysis or transplant (4-variable Tangri equation).
mL/min
mg/g
Hemoglobin
A1c (HbA1c) Converter
Translates the HbA1c percentage used in diabetes monitoring into
an "estimated
average glucose" (eAG) value that patients can more easily
relate to their daily
meter readings. Note that HbA1c (and thus this calculation) can
be misleading in
the presence of hemoglobinopathies or anemia.
%
mmol/mol
AST to Platelet Ratio Index (APRI) Score
Used primarily in Hepatitis C and chronic liver patients to
predict the risk of
fibrosis and cirrhosis without invasive biopsies. While highly
successful at
excluding cirrhosis due to its high negative predictive value,
beware of false
positives during acute hepatitis flares when AST levels
temporarily spike.
Wai CT, et al. A simple noninvasive index can
predict both significant fibrosis and cirrhosis in
patients with chronic hepatitis C. Hepatology. 2003.
(PMID: 12883497)
Lin ZH, et al. Performance of low-cost non-invasive
biomarkers of liver fibrosis in patients with
chronic hepatitis C. Eur J Gastroenterol Hepatol.
2011. (PMID: 21941102)
U/L
U/L
10³/µL
Winters
Formula (Metabolic Acidosis Compensation)
Monitors whether the body's respiratory response (compensation)
is at the
expected level in patients with metabolic acidosis. If the
measured pCO2 differs
from the calculated value, it indicates a concurrent hidden
respiratory acidosis
or alkalosis (mixed disorder).
Albert MS, et al. Quantitative displacement of
acid-base equilibrium in metabolic acidosis. Ann
Intern Med. 1967. (PMID: 6016545)
Calculates expected pCO2 in primary metabolic acidosis. Compare
with measured
pCO2
to detect
concurrent respiratory disorder.
mEq/L
mmHg
Excel
Decimal Format Tip
Please ensure that uploaded Excel files use a
dot (.) as the decimal
separator.
Values containing commas (e.g., 5,5)
may be
skipped.
Excel
Setting: Go to File > Options >
Advanced. Uncheck "Use system
separators" and set Decimal
separator to "."
(dot).
Levey-Jennings Simulator
Levey-Jennings Chart is used to
monitor QC
performance over
time.
Enter data manually or upload via Excel. Use
dots
(.) as decimal
separators.
Select Westgard rules to detect out-of-control
conditions.
How to
Use:
Enter Mean and
SD values
(or
select
"Calculate
from data")
Upload QC data via Excel
file or enter
values
manually
Select applicable Westgard
Rules for
violation
detection
Click "CALCULATE &
PLOT" to
generate the
L-J chart
Review the chart for rule violations
(marked
with different
colors)
Note: The "Auto" settings
utilize optimized parameters derived from
the data in the medical specialty thesis
titled "Patient-based real-time
quality control management enhanced with
biological variation data" by
MD. Belgin BAYRAM (ŞARA).
How to
Use:
Select the Analyte (or
choose Custom for
manual
entry)
Upload patient data via Excel
file or enter
values
manually
Choose EWMA or MA
method
(or use Auto)
Adjust truncation and log transformation
options if needed
Click "CALCULATE &
PLOT" to
generate the
control
chart
Review for out-of-control signals
(points
exceeding control
limits)
Parameter
Abbreviations:
EWMA – Exponentially
Weighted Moving
Average
MA – Moving Average
λ (Lambda) – Smoothing
factor for EWMA (0
to 1)
L – Control limit
multiplier for EWMA
w (Window) – Number of
observations for MA
calculation
RCV – Reference Change
Value for truncation
limits
No
Value
...
Sigma Metric &
Method
Decision
Sigma Metric evaluates method
performance using Six
Sigma
methodology.
A Sigma value ≥6 indicates world-class
performance,
while ≤3
requires
improvement.
Use Pooled CV for average performance or
Separate
for individual QC
levels.
How to
Use:
Select Pooled CV or
Separate
CV
calculation mode
Enter CV% from your QC
data
(imprecision)
Enter Bias% from EQA/PT
or
method
comparison
Enter TEa (Total
Allowable
Error) from
CLIA/EFLM
guidelines
Click "CALCULATE" to
compute Sigma value
Interpret result using Sigma scale (≥6
world-class, <3 poor)
Parameter
Abbreviations:
CV% – Coefficient of
Variation
(imprecision, from
QC
data)
Bias% – Systematic
error
(from EQA/PT or
method
comparison)
TEa – Total Allowable
Error
(quality
requirement,
from
CLIA/EFLM)
Carryover Analysis detects
sample-to-sample
contamination.
Run samples in the specified sequence
(H-L-L-H
pattern) and
enter
results.
If the difference exceeds TEa or 3×SD,
carryover
is significant.
How
to
Use:
Enter TEa (Total
Allowable Error) for
the
analyte
Run samples in sequence: H1
→ L1
→ L2 → L3 → H2
→ L4 →
L5 →
L6
Enter all measured values in the
respective fields
Click "CALCULATE"
to
analyze carryover
Review Group A (L after L) vs Group
B (L
after H)
differences
Parameter
Abbreviations:
H – High
concentration
sample
L – Low
concentration
sample
TEa – Total
Allowable
Error (acceptance
limit)
Group A (L after L)
–
Low samples
measured
after
other low
samples
Group B (L after H)
–
Low samples
measured
after
high samples
Reference Change Value
(RCV)
determines if a
change
between
two serial
patient results is clinically significant.
Uses biological variation data to calculate
the
expected
variation.
How
to
Use:
Enter Patient's Previous
Result
(baseline
value)
Enter Patient's Current
Result (new
measurement)
Enter CVi, CVg, CVa
values (from
biological
variation database)
Select Z-score for
desired significance
level
Click "CALCULATE"
to
compute RCV
Compare % difference with RCV to
determine clinical
significance
Bland-Altman Analysis
assesses
agreement
between
two
measurement methods.
Upload an Excel file with paired
measurements or enter
data
manually.
The plot shows the difference between
methods against
their
mean.
How to Use:
Enter Method
names for labeling
purposes
Upload paired data via
Excel
file or
add
manually
Select Parametric or
Non-Parametric
analysis method
Optionally enter
Allowable
Difference
for
clinical
acceptability
Click "CALCULATE &
PLOT" to
generate
Bland-Altman plot
Review Bias, LoA, proportional
bias, and
clinical
interpretation
Methodology
Guide
1.
Data
Preparation
(Mean &
Difference):
X-Axis
(Mean):
Average
of two
methods:
(A+B)/2. If
one method is
the "gold
standard", you
may use only the
reference value on
X-axis, but
this
can be
misleading.
Y-Axis
(Difference):
Difference
between
measurements:
A−B
2.
Statistical
Parameters:
Mean Difference
(Bias):
Arithmetic
mean of all
differences (d̄). Shows
average
over/underestimation.
Standard
Deviation
(s):
SD of
differences
measures variability.
Limits of
Agreement
(LoA):
Range
containing 95%
of differences:
Bias ± 1.96 × SD
3.
Graph
Components:
Zero
Line:
Horizontal
line at
Y=0
(represents
perfect agreement)
Bias
Line:
Horizontal
line at
mean
difference
(d̄)
LoA
Lines:
Dashed lines
showing
upper and lower
limits
Data
Points:
Each
paired
measurement plotted at
(mean, difference)
4.
Important
Checks:
Normality
Check:
Differences
should
be normally
distributed (use
Shapiro-Wilk test). If
not,
consider log
transformation.
Percentage
Difference:
If
differences increase
with magnitude
(proportional error),
express as
%
difference.
A Priori
Limits:
Clinical
acceptability must be
defined BEFORE
analysis—Bland-Altman
only
describes,
not
decides.
Confidence
Intervals:
Add 95%
CI
for Bias and
LoA to show estimation
precision.
Parameter
Abbreviations:
Bias – Mean
difference between
methods
(systematic
error)
SD – Standard
Deviation of
differences
LoA – Limits of
Agreement (Mean
±
1.96×SD),
contains
95% of differences
95% CI –
Confidence Interval
for Bias
and
LoA
r – Correlation
coefficient for
proportional bias
detection
Important:
If LoA falls within clinically
acceptable
limits,
methods
are
interchangeable.
If Bias CI does not include
zero, systematic
bias is
present.
High correlation (r≈1)
does NOT mean
good
agreement!
Correlation measures linear
relationship, not
agreement.
Clinical acceptability limits
must be defined
a
priori
(before analysis).
Selection Guide: Absolute vs.
Percent
Difference
1. Choose Absolute
Difference
(Units)
if
the
measurement
error remains constant
regardless of the value
(Homoscedasticity).
Best for:
Electrolytes (Sodium,
Calcium),
pH,
or analytes
with
a narrow clinical range.
2. Choose Percent
Difference
(%) if the
measurement
error
increases as the concentration
increases
(Proportional
Bias).
Best for: Enzymes
(ALT, AST, ALP),
Glucose,
Hormones (PSA,
TSH,
HCG), or analytes with very wide
measurement
ranges.
Practical Tip:
Observe the
Trend
Analysis
in results.
If
Proportional Bias is
detected
(correlation r >
0.3), switching
to
Percent Difference (%) often
provides a more
reliable
assessment of
clinical
agreement.
3. X-Axis
Selection: • Mean of Both
Methods:
Standard
for
most cases. It
provides
the best estimate of the true
value when both
methods
have
error.
• Comparative Method
Only:
Use ONLY
if
Method 2 is
a
"Gold Standard" (Reference
Method) with
near-zero error.
No
Method 1
Method 2
Mean
Diff
...
If
LoA
exceeds this
limit,
methods
are not interchangeable
Tip: Use
Percent
Difference when
comparing methods
across a wide measurement range to
detect
proportional bias.
Parametric: For
normally
distributed
differences
|
Non-Parametric:
When normality is
not met
Correlation
Plot
(Method 1 vs
Method 2)
Useful Websites
Clinical References & Handbook
Lab Handbook
Official legislation, technical documents, and laboratory internal protocols.
Mayo Clinic
Comprehensive test catalog with detailed clinical significance and interpretation.
UpToDate
Evidence-based clinical decision support tool for medical professionals.
BiliTool
Management of neonatal hyperbilirubinemia based on AAP guidelines.
CALIPER
Comprehensive database for pediatric reference intervals and variations.
Lab Online
Detailed information on laboratory tests and pathological conditions.
Quality & Standards
Westgard QC
The standard resource for laboratory quality control rules and management.
EFLM
Database for biological variation and performance specifications.
IFCC
International federation for clinical chemistry and laboratory medicine.
Harmonization
Global resources for the harmonization of clinical laboratory test results.
ADLM
Association for Diagnostics & Laboratory Medicine (formerly AACC).
Academic & News
D. Young
Effects of drugs and diseases on clinical laboratory tests (Archive).
CAP Today
The latest news and trends in laboratory medicine and pathology.
LabRoots
Scientific webinars, virtual events, and latest research updates.
CLD
Comprehensive textbook and reference for laboratory diagnostics.
Medscape
Specialized news and clinical information for pathology and lab medicine.
Societies & Apps
TBD
Official website of the Turkish Biochemical Society.
TKBD
Society of Clinical Biochemistry Specialists in Turkey.
KBUD
Association of Clinical Biochemistry Professionals.
Error Finder
Tool for identifying and analyzing pre-analytical laboratory errors.
QC Const.
Internal quality control visualization and management app.
Journals
Please
select
the
journals
you
wish to
follow and the number of recent articles
to display,
then click
Lab
Digest
to
continue.