Reference
The exam hands you a lab sheet and expects the formulas. Knowing both cold is time you get back on every question that needs them.
136 to 146 mEq/L
136 to 146 mmol/L
Reflects free water balance, not sodium content. Correct by 1.6 mEq/L for every 100 mg/dL of glucose above normal.
3.5 to 5.0 mEq/L
3.5 to 5.0 mmol/L
Small serum changes reflect large total-body shifts, because most potassium is intracellular.
95 to 105 mEq/L
95 to 105 mmol/L
22 to 28 mEq/L
22 to 28 mmol/L
7 to 18 mg/dL
2.5 to 6.4 mmol/L
A ratio to creatinine above 20:1 suggests a prerenal cause.
0.6 to 1.2 mg/dL
53 to 106 umol/L
An insensitive early marker: filtration can fall by half before it leaves the normal range.
70 to 100 mg/dL
3.8 to 5.6 mmol/L
8.4 to 10.2 mg/dL
2.1 to 2.6 mmol/L
Correct for albumin, or the value misleads in liver disease and nephrosis.
1.5 to 2.0 mEq/L
0.75 to 1.0 mmol/L
Low magnesium makes hypokalemia and hypocalcemia refractory until it is replaced.
3.0 to 4.5 mg/dL
1.0 to 1.5 mmol/L
Moves opposite to calcium under parathyroid hormone.
6.0 to 7.8 g/dL
60 to 78 g/L
3.5 to 5.5 g/dL
35 to 55 g/L
The main determinant of plasma oncotic pressure.
0.1 to 1.0 mg/dL
2 to 17 umol/L
0.0 to 0.3 mg/dL
0 to 5 umol/L
The conjugated fraction. Elevated in obstruction and hepatocellular disease, normal in hemolysis and Gilbert syndrome.
8 to 20 U/L
A ratio to alanine aminotransferase above 2:1 suggests alcoholic liver disease.
8 to 20 U/L
More liver-specific than aspartate aminotransferase.
20 to 70 U/L
Also rises from bone and placenta; gamma-glutamyl transferase separates the sources.
25 to 125 U/L
14 to 280 U/L
More specific for pancreatitis than amylase and stays elevated longer.
3.0 to 8.2 mg/dL
0.18 to 0.48 mmol/L
Below 200 mg/dL desirable
Below 5.2 mmol/L
Below 150 mg/dL
Below 1.7 mmol/L
Above roughly 1000 mg/dL, pancreatitis becomes a real risk.
275 to 295 mOsm/kg
Compare measured with calculated to find an osmolar gap.
Male 25 to 90 U/L, female 10 to 70 U/L
Below 0.04 ng/mL
Rises about 3 hours after myocardial injury and stays elevated for days.
45 to 200 U/L
Non-specific. Rises in hemolysis, tumour lysis and Pneumocystis pneumonia.
Male 13.5 to 17.5 g/dL, female 12.0 to 16.0 g/dL
Male 41 to 53 percent, female 36 to 46 percent
80 to 100 fL
The first branch point in any anemia: below 80 microcytic, above 100 macrocytic.
4,500 to 11,000/mm3
150,000 to 400,000/mm3
Spontaneous bleeding is uncommon above 20,000.
0.5 to 1.5 percent
Correct for anemia before interpreting; it separates production failure from destruction.
Male 0 to 15 mm/h, female 0 to 20 mm/h
Above 50 with a new headache in an older patient should prompt thinking about giant cell arteritis.
11 to 15 seconds
The extrinsic pathway. Prolonged first in vitamin K deficiency and liver disease, because factor VII has the shortest half-life.
25 to 40 seconds
The intrinsic pathway. A mixing study separates a missing factor from an inhibitor.
Male 20 to 250 ng/mL, female 10 to 120 ng/mL
The single most useful iron study, but it is an acute phase reactant and rises with inflammation.
50 to 170 ug/dL
250 to 400 ug/dL
Rises in true iron deficiency and falls in anemia of chronic disease.
200 to 800 pg/mL
When borderline, methylmalonic acid settles it.
2.5 to 20 ng/mL
7.35 to 7.45
Decide the primary disturbance from the direction of the pH, then check whether compensation is appropriate.
75 to 105 mm Hg
33 to 45 mm Hg
Set entirely by alveolar ventilation.
22 to 28 mEq/L
95 to 100 percent
Normal in carbon monoxide poisoning on pulse oximetry, which is the trap.
70 to 180 mm H2O
40 to 70 mg/dL
Interpret against a simultaneous serum glucose; the normal ratio is about two-thirds. Low means bacteria, mycobacteria or fungi.
Below 40 mg/dL
Raised with few cells is albuminocytologic dissociation, the pattern in Guillain-Barre syndrome.
0 to 5 cells/mm3
Neutrophil predominance suggests bacteria, lymphocytic suggests viral, mycobacterial or fungal.
1.003 to 1.030
Maximally dilute urine in the face of hypernatremia points at diabetes insipidus.
50 to 1200 mOsm/kg
Below 150 mg/24 h
Above 3.5 g/24 h is nephrotic range.
Male 97 to 137 mL/min, female 88 to 128 mL/min
0.4 to 4.0 uU/mL
The most sensitive early marker of thyroid dysfunction: it moves before free thyroxine does.
0.9 to 1.7 ng/dL
5 to 23 ug/dL
A single random value is uninterpretable because of the diurnal rhythm.
10 to 60 pg/mL
Interpret only alongside calcium; the pair is what makes the diagnosis.
Below 5.7 percent
Reflects roughly three months of glycemia, the lifespan of a red cell. Misleads in hemolysis and recent transfusion.
Reference ranges vary between laboratories. These are the conventional adult ranges in the form the exam presents them, and a real report should always be read against the range printed on it. Nothing here is medical advice.