Chemistry & Electrolytes

Predict the change in serum sodium from one litre of a chosen infusate, using the Adrogué-Madias formula.

Convert albumin between g/dL, g/L and µmol/L, and see why a low albumin marks the severity of illness rather than nutritional state.

Convert serum amylase between U/L, IU/L, µkat/L and nkat/L, and see why a normal amylase does not exclude pancreatitis and a very high one does not mean a severe attack.

Convert bicarbonate between mmol/L, mEq/L and mg/dL. Bicarbonate is monovalent, so mmol/L and mEq/L are the same number — the harder question is which bicarbonate your report means.

Calculate the calcium-phosphate product, a legacy marker of vascular calcification risk in chronic kidney disease.

Calculate serum osmolality from sodium, glucose, BUN and ethanol to compare against the measured value and detect an osmolal gap.

Convert ceruloplasmin between mg/dL, g/L, mg/L and µmol/L, and see why a normal level does not exclude Wilson disease.

Convert chloride between mmol/L, mEq/L and mg/dL. Chloride is monovalent, so mmol/L and mEq/L are the same number — and the result only means something once it is read against sodium.

Convert plasma (pseudo)cholinesterase between U/L, IU/L, µkat/L and nkat/L, and keep it separate from the red-cell acetylcholinesterase used in organophosphate poisoning.

Convert creatine kinase between U/L, IU/L, µkat/L and nkat/L, with the statin and rhabdomyolysis thresholds and why one reference interval does not fit everyone.

Calculate the free water deficit in hypernatraemia from body weight, measured sodium and total body water fraction.

Calculate globulin as total protein minus albumin, with the A:G ratio and what a reversed ratio actually tells you about the two components.

Convert LDH between U/L, IU/L, µkat/L and nkat/L — and start with the fact that haemolysing the sample raises the result all by itself.

Convert serum lipase between U/L, IU/L, µkat/L and nkat/L, with the three-times-upper-limit diagnostic threshold and why the height of the rise says nothing about severity.

Magnesium is divalent: mEq/L is exactly twice mmol/L, and mg/dL is a different scale again. Convert between all three without making the twofold error.

Convert potassium between mmol/L, mEq/L and mg/dL. Potassium is monovalent, so mmol/L and mEq/L are the same number — the real risk on this test is the sample, not the arithmetic.

Correct measured sodium for the diluting effect of hyperglycaemia, using either the Katz or Hillier factor.

Calculate the sodium deficit in hyponatraemia between a measured and target sodium, with correction rate limits.

Convert sodium between mmol/L, mEq/L and mg/dL. Sodium is monovalent, so mmol/L and mEq/L are the same number — and the mg/dL column is the one that needs care.

Convert serum total protein between g/dL, g/L and mg/dL — and use it the way it is meant to be used, subtracted from albumin to give the globulin and the A:G ratio.

Convert urate between mg/dL, µmol/L and mmol/L — and keep two different numbers apart: the sex-specific reference interval, and the 360 µmol/L treat-to-target used in gout.