| Laboratory test | Frequency |
| Hemoglobin, hematocrit | After the infant is receiving enteral iron supplementation, measure every 2 weeks until results are stable. Recheck prior to hospital discharge. |
| Calcium, phosphorus, alkaline phosphatase | In infants <1500 g birth weight, measure starting at 5 to 6 weeks of age. Measure weekly until alkaline phosphatase is <600 IU/L and serum phosphorus is >4.5 mg/dL. Once stable beyond these thresholds, no need to repeat. |
| BUN | Measure in infants with poor growth. BUN <10 mg/dL may suggest the need for more protein intake. |
| Serum electrolytes | In selected infants (those receiving diuretics, or feeds of unfortified human milk, or limited intake, or slow growth). |
